Adds the current code.

It's been running for close to a month on one of the IRC channels I
frequent and seems to be working fine.
One should be aware that, among other missing features, this version
does not store permanently what the bot learns. Indeed, I am currently
using a file with 431848 lines as its initial knowledge bank, making
this particular feature not a high priority one.
Also consider the fact that Zero of One converts text to underscore
before reading it but will not change its own aliases. This could
potentially be a cause for surprises when using uppercase letters in the
latter.

26 files changed, 3183 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..ba70690
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 2.8 FATAL_ERROR)
+
+project("Zero of One")
+
+include(FindPkgConfig)
+
+add_subdirectory(src)
+set(CMAKE_C_FLAGS "-D_POSIX_SOURCE -std=c99 -O2")
+# ${SRC_FILES} is recursively defined in the subdirectories.
+# Each subdirectory only adds the source files that are present at its level.
+add_executable(zero_of_one ${SRC_FILES})
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
new file mode 100644
index 0000000..76a73ed
--- /dev/null
+++ b/src/CMakeLists.txt
@@ -0,0 +1,5 @@
+add_subdirectory(core)
+add_subdirectory(io)
+add_subdirectory(tool)
+
+set(SRC_FILES ${SRC_FILES} PARENT_SCOPE)
diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
new file mode 100644
index 0000000..2722355
--- /dev/null
+++ b/src/core/CMakeLists.txt
@@ -0,0 +1,10 @@
+set(
+   SRC_FILES ${SRC_FILES}
+   ${CMAKE_CURRENT_SOURCE_DIR}/main.c
+   ${CMAKE_CURRENT_SOURCE_DIR}/knowledge.c
+   ${CMAKE_CURRENT_SOURCE_DIR}/assimilate.c
+   ${CMAKE_CURRENT_SOURCE_DIR}/create_sentences.c
+)
+
+set(SRC_FILES ${SRC_FILES} PARENT_SCOPE)
+
diff --git a/src/core/assimilate.c b/src/core/assimilate.c
new file mode 100644
index 0000000..eb6aa17
--- /dev/null
+++ b/src/core/assimilate.c
@@ -0,0 +1,232 @@
+#include <stdlib.h>
+#include <string.h>
+
+#include "../io/error.h"
+
+#include "knowledge.h"
+
+static int link_to
+(
+   ZoO_index links_count [const restrict static 1],
+   ZoO_index * links_occurrences [const restrict static 1],
+   ZoO_index * links [const restrict static 1],
+   ZoO_index const target
+)
+{
+   ZoO_index i, * new_p;
+
+   for (i = 0; i < *links_count; ++i)
+   {
+      if ((*links)[i] == target)
+      {
+         if ((*links_occurrences)[i] == ZoO_INDEX_MAX)
+         {
+            ZoO_S_WARNING
+            (
+               "Maximum link occurrences count has been reached."
+            );
+
+            return -1;
+         }
+
+         (*links_occurrences)[i] += 1;
+
+         return 0;
+      }
+   }
+
+   if (*links_count == ZoO_INDEX_MAX)
+   {
+      ZoO_S_WARNING("Maximum links count has been reached.");
+
+      return -1;
+   }
+
+   new_p =
+      (ZoO_index *) realloc
+      (
+         *links_occurrences,
+         (
+            (
+               /* Safe: *links_count < ZoO_INDEX_MAX */
+               (size_t) (*links_count + 1)
+            )
+            * sizeof(ZoO_index)
+         )
+      );
+
+   if (new_p == (ZoO_index *) NULL)
+   {
+      ZoO_S_ERROR("Could not reallocate a link occurrences list.");
+
+      return -1;
+   }
+
+   new_p[*links_count] = 1;
+
+   *links_occurrences = new_p;
+
+   new_p =
+      (ZoO_index *) realloc
+      (
+         *links,
+         (
+            (
+               /* Safe: *links_count < ZoO_INDEX_MAX */
+               (size_t) (*links_count + 1)
+            ) * sizeof(ZoO_index)
+         )
+      );
+
+   if (new_p == (ZoO_index *) NULL)
+   {
+      ZoO_S_ERROR("Could not reallocate a link list.");
+
+      return -1;
+   }
+
+   new_p[*links_count] = target;
+
+   *links = new_p;
+
+   *links_count += 1;
+
+   return 0;
+}
+
+static int link_words
+(
+   struct ZoO_knowledge k [const restrict static 1],
+   ZoO_index const a,
+   ZoO_index const b
+)
+{
+   int error;
+
+   error =
+      link_to
+      (
+         &(k->words[a].forward_links_count),
+         &(k->words[a].forward_links_occurrences),
+         &(k->words[a].forward_links),
+         b
+      );
+
+   error =
+      (
+         link_to
+         (
+            &(k->words[b].backward_links_count),
+            &(k->words[b].backward_links_occurrences),
+            &(k->words[b].backward_links),
+            a
+         )
+         | error
+      );
+
+   return error;
+}
+
+int ZoO_knowledge_assimilate
+(
+   struct ZoO_knowledge k [const static 1],
+   struct ZoO_strings string [const restrict static 1],
+   ZoO_index const aliases_count,
+   const char * restrict aliases [const restrict static aliases_count]
+)
+{
+   int error;
+   ZoO_index curr_word, next_word;
+   ZoO_index curr_word_id, next_word_id;
+
+   curr_word = 0;
+
+   if (string->words_count == 0)
+   {
+      return 0;
+   }
+
+   for (curr_word = 0; curr_word < aliases_count; ++curr_word)
+   {
+      if (ZoO_IS_PREFIX(aliases[curr_word], string->words[0]))
+      {
+         return 0;
+      }
+   }
+
+   curr_word = 0;
+
+   if (ZoO_knowledge_learn(k, string->words[curr_word], &curr_word_id) < 0)
+   {
+      return -1;
+   }
+
+   if (link_words(k, ZoO_WORD_START_OF_LINE, curr_word_id) < 0)
+   {
+      error = -1;
+
+      ZoO_WARNING
+      (
+         "Could not indicate that '"
+         ZoO_CHAR_STRING_SYMBOL
+         "' was the first word of the sentence.",
+         string->words[0]
+      );
+   }
+
+   next_word = 1;
+
+   error = 0;
+
+   while (next_word < string->words_count)
+   {
+      /* prevents words [restrict], k [restrict] */
+      if (ZoO_knowledge_learn(k, string->words[next_word], &next_word_id) < 0)
+      {
+         return -1;
+      }
+
+      if (link_words(k, curr_word_id, next_word_id) < 0)
+      {
+         error = -1;
+
+         ZoO_WARNING
+         (
+            "Could not add a link between words '"
+            ZoO_CHAR_STRING_SYMBOL
+            "' and '"
+            ZoO_CHAR_STRING_SYMBOL
+            "'.",
+            string->words[curr_word],
+            string->words[next_word]
+         );
+      }
+
+      curr_word = next_word;
+      curr_word_id = next_word_id;
+      /*
+       * Safe:
+       *  - next_word < words_count
+       *  - words_count =< ZoO_INDEX_MAX
+       *  ----
+       *  next_word < ZoO_INDEX_MAX
+       */
+      next_word += 1;
+   }
+
+   if (link_words(k, curr_word_id, ZoO_WORD_END_OF_LINE) < 0)
+   {
+      error = -1;
+
+      ZoO_WARNING
+      (
+         "Could not indicate that '"
+         ZoO_CHAR_STRING_SYMBOL
+         "' was the last word of the sentence.",
+         string->words[curr_word_id]
+      );
+   }
+
+   return error;
+}
+
diff --git a/src/core/create_sentences.c b/src/core/create_sentences.c
new file mode 100644
index 0000000..bc410e5
--- /dev/null
+++ b/src/core/create_sentences.c
@@ -0,0 +1,486 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h> /* defines SIZE_MAX */
+
+#include "../io/error.h"
+
+#include "knowledge.h"
+
+static ZoO_index pick_an_index
+(
+   ZoO_index const occurrences,
+   const ZoO_index links_occurrences [const restrict static 1],
+   const ZoO_index links [const restrict static 1]
+)
+{
+   ZoO_index result, accumulator, random_number;
+
+   result = 0;
+   accumulator = links_occurrences[0];
+   random_number = (((ZoO_index) rand()) % occurrences);
+
+   while (accumulator < random_number)
+   {
+
+      /*
+       * Should be safe:
+       * result overflowing <-> sum('links_occurrences') > 'occurrences'
+       * and sum('links_occurrences') == 'occurrences'
+       */
+      result += 1;
+
+      /*
+       * Should be safe:
+       *  - sum('links_occurrences') == 'occurrences'.
+       *  - 'occurrences' is safe.
+       *  ----
+       *  'accumulator' is safe.
+       */
+      accumulator += links_occurrences[result];
+   }
+
+   return links[result];
+}
+
+static unsigned char * extend_left
+(
+   struct ZoO_knowledge k [const restrict static 1],
+   ZoO_index word_id,
+   ZoO_char current_sentence [static 1],
+   size_t sentence_size [const restrict static 1],
+   ZoO_index credits [const static 1]
+)
+{
+   size_t addition_size;
+   struct ZoO_knowledge_word * w;
+   ZoO_char * next_sentence;
+
+   w = (k->words + word_id);
+
+   if
+   (
+      (w->special == ZoO_WORD_STARTS_SENTENCE)
+      || (w->occurrences == 0)
+   )
+   {
+      return current_sentence;
+   }
+
+   /* prevents current_sentence [restrict] */
+   next_sentence = current_sentence;
+
+   for (;;)
+   {
+      if (*credits == 0)
+      {
+         return current_sentence;
+      }
+
+      *credits -= 1;
+      word_id =
+         pick_an_index
+         (
+            w->occurrences,
+            w->backward_links_occurrences,
+            w->backward_links
+         );
+
+      w = (k->words + word_id);
+
+      switch (w->special)
+      {
+         case ZoO_WORD_HAS_NO_EFFECT:
+            /* FIXME: not overflow-safe. */
+            /* word also contains an '\0', which we will replace by a ' ' */
+            addition_size = w->word_size;
+            break;
+
+         case ZoO_WORD_ENDS_SENTENCE:
+            ZoO_S_WARNING("END OF LINE should not be prefixable.");
+            return current_sentence;
+
+         case ZoO_WORD_STARTS_SENTENCE:
+            return current_sentence;
+
+         case ZoO_WORD_REMOVES_LEFT_SPACE:
+         case ZoO_WORD_REMOVES_RIGHT_SPACE:
+            /* word also contains an '\0', which we will remove. */
+            addition_size = w->word_size - 1;
+            break;
+      }
+
+      if (*sentence_size > (SIZE_MAX - addition_size))
+      {
+         ZoO_S_WARNING
+         (
+            "Sentence construction aborted to avoid size_t overflow."
+         );
+
+         return current_sentence;
+      }
+
+      next_sentence =
+         (ZoO_char *) calloc
+         (
+            /* overflow-safe */
+            (*sentence_size + addition_size),
+            sizeof(ZoO_char)
+         );
+
+      if (next_sentence == (ZoO_char *) NULL)
+      {
+         ZoO_S_ERROR("Could not allocate memory to store new sentence.");
+
+         return current_sentence;
+      }
+
+      /* overflow-safe */
+      *sentence_size = (*sentence_size + addition_size);
+
+      switch (w->special)
+      {
+         case ZoO_WORD_HAS_NO_EFFECT:
+            snprintf
+            (
+               next_sentence,
+               *sentence_size,
+               " " ZoO_CHAR_STRING_SYMBOL ZoO_CHAR_STRING_SYMBOL,
+               w->word,
+               current_sentence
+            );
+            break;
+
+         case ZoO_WORD_REMOVES_LEFT_SPACE:
+            snprintf
+            (
+               next_sentence,
+               *sentence_size,
+               ZoO_CHAR_STRING_SYMBOL ZoO_CHAR_STRING_SYMBOL,
+               w->word,
+               current_sentence
+            );
+            break;
+
+         case ZoO_WORD_REMOVES_RIGHT_SPACE:
+            snprintf
+            (
+               next_sentence,
+               *sentence_size,
+               ZoO_CHAR_STRING_SYMBOL ZoO_CHAR_STRING_SYMBOL,
+               w->word,
+               /* Safe: strlen(current_sentence) >= 2 */
+               (current_sentence + 1)
+            );
+            break;
+
+         default:
+            /* TODO: PROGRAM LOGIC ERROR */
+            break;
+      }
+
+      free((void *) current_sentence);
+
+      /* prevents current_sentence [const] */
+      current_sentence = next_sentence;
+   }
+}
+
+static unsigned char * extend_right
+(
+   struct ZoO_knowledge k [const restrict static 1],
+   ZoO_index word_id,
+   ZoO_char current_sentence [static 1],
+   size_t sentence_size [const restrict static 1],
+   ZoO_index credits [const static 1]
+)
+{
+   size_t addition_size;
+   struct ZoO_knowledge_word * w;
+   ZoO_char * next_sentence;
+
+   w = (k->words + word_id);
+
+   if
+   (
+      (w->special == ZoO_WORD_ENDS_SENTENCE)
+      || (w->occurrences == 0)
+   )
+   {
+      return current_sentence;
+   }
+
+   /* prevents current_sentence [restrict] */
+   next_sentence = current_sentence;
+
+   for (;;)
+   {
+      if (*credits == 0)
+      {
+         return current_sentence;
+      }
+
+      *credits -= 1;
+
+      word_id =
+         pick_an_index
+         (
+            w->occurrences,
+            w->forward_links_occurrences,
+            w->forward_links
+         );
+
+      w = (k->words + word_id);
+
+      switch (w->special)
+      {
+         case ZoO_WORD_HAS_NO_EFFECT:
+            /* FIXME: Assumed to be overflow-safe. */
+            /* word also contains an '\0', which we will replace by a ' '. */
+            addition_size = w->word_size;
+            break;
+
+         case ZoO_WORD_ENDS_SENTENCE:
+            return current_sentence;
+
+         case ZoO_WORD_STARTS_SENTENCE:
+            ZoO_S_WARNING("START OF LINE should not be suffixable.");
+            return current_sentence;
+
+         case ZoO_WORD_REMOVES_LEFT_SPACE:
+         case ZoO_WORD_REMOVES_RIGHT_SPACE:
+            /* word also contains an '\0', which we will remove. */
+            addition_size = w->word_size - 1;
+            break;
+      }
+
+      if (*sentence_size > (SIZE_MAX - addition_size))
+      {
+         ZoO_S_WARNING
+         (
+            "Sentence construction aborted to avoid size_t overflow."
+         );
+
+         return current_sentence;
+      }
+
+      next_sentence =
+         (ZoO_char *) calloc
+         (
+            /* overflow-safe */
+            (*sentence_size + addition_size),
+            sizeof(ZoO_char)
+         );
+
+      if (next_sentence == (ZoO_char *) NULL)
+      {
+         ZoO_S_ERROR("Could not allocate memory to store new sentence.");
+
+         return current_sentence;
+      }
+
+      /* overflow-safe */
+      *sentence_size = (*sentence_size + addition_size);
+
+      switch (w->special)
+      {
+         case ZoO_WORD_REMOVES_LEFT_SPACE:
+            printf
+            (
+               "current sentence:'%s', pointing at '%c'.\n",
+               current_sentence,
+               current_sentence[*sentence_size - addition_size - 2]
+            );
+            current_sentence[*sentence_size - addition_size - 2] = '\0';
+
+         case ZoO_WORD_HAS_NO_EFFECT:
+            snprintf
+            (
+               next_sentence,
+               *sentence_size,
+               ZoO_CHAR_STRING_SYMBOL ZoO_CHAR_STRING_SYMBOL " ",
+               current_sentence,
+               w->word
+            );
+            break;
+
+         case ZoO_WORD_REMOVES_RIGHT_SPACE:
+            snprintf
+            (
+               next_sentence,
+               *sentence_size,
+               ZoO_CHAR_STRING_SYMBOL ZoO_CHAR_STRING_SYMBOL,
+               current_sentence,
+               w->word
+            );
+            break;
+
+         default:
+            /* TODO: PROGRAM LOGIC ERROR */
+            break;
+      }
+
+      free((void *) current_sentence);
+
+      /* prevents current_sentence [const] */
+      current_sentence = next_sentence;
+   }
+}
+
+int ZoO_knowledge_extend
+(
+   struct ZoO_knowledge k [const static 1],
+   const struct ZoO_strings string [const static 1],
+   int const ignore_first_word,
+   ZoO_char * result [const static 1]
+)
+{
+   int word_found;
+   size_t sentence_size;
+   ZoO_index i, word_id, word_min_score, word_min_id, credits;
+
+   word_found = 0;
+   credits = ZoO_MAX_REPLY_WORDS;
+
+   if (ignore_first_word)
+   {
+      i = 1;
+   }
+   else
+   {
+      i = 0;
+   }
+
+   for (; i < string->words_count; ++i)
+   {
+      /* prevents k [restrict] */
+      if (ZoO_knowledge_find(k, string->words[i], &word_min_id) == 0)
+      {
+         word_found = 1;
+         word_min_score = k->words[word_min_id].occurrences;
+
+         break;
+      }
+   }
+
+   if (word_found == 0)
+   {
+      word_min_id = (rand() % k->words_count);
+      word_min_score = k->words[word_min_id].occurrences;
+   }
+
+   for (; i < string->words_count; ++i)
+   {
+      if
+      (
+         (ZoO_knowledge_find(k, string->words[i], &word_id) == 0)
+         && (k->words[word_id].occurrences < word_min_score)
+      )
+      {
+         word_min_score = k->words[word_id].occurrences;
+         word_min_id = word_id;
+      }
+   }
+
+   /* 3: 2 spaces + '\0' */
+   /* FIXME: not overflow-safe */
+   switch (k->words[word_min_id].special)
+   {
+      case ZoO_WORD_REMOVES_LEFT_SPACE:
+      case ZoO_WORD_REMOVES_RIGHT_SPACE:
+         /* word + ' ' + '\0' */
+         sentence_size = (strlen(k->words[word_min_id].word) + 2);
+         break;
+
+      case ZoO_WORD_HAS_NO_EFFECT:
+         /* word + ' ' * 2 + '\0' */
+         sentence_size = (strlen(k->words[word_min_id].word) + 3);
+         break;
+
+      default:
+         ZoO_WARNING
+         (
+            "'%s' was unexpectedly selected as pillar.",
+            k->words[word_min_id].word
+         );
+         /* word + '[' + ']' + ' ' * 2 + '\0' */
+         sentence_size = (strlen(k->words[word_min_id].word) + 5);
+         break;
+   }
+
+   *result = (ZoO_char *) calloc(sentence_size, sizeof(ZoO_char));
+
+   if (*result == (ZoO_char *) NULL)
+   {
+      ZoO_S_ERROR("Could not allocate memory to start sentence.");
+
+      return -2;
+   }
+
+   switch (k->words[word_min_id].special)
+   {
+      case ZoO_WORD_REMOVES_LEFT_SPACE:
+         snprintf
+         (
+            *result,
+            sentence_size,
+            ZoO_CHAR_STRING_SYMBOL " ",
+            k->words[word_min_id].word
+         );
+         break;
+
+      case ZoO_WORD_REMOVES_RIGHT_SPACE:
+         snprintf
+         (
+            *result,
+            sentence_size,
+            " " ZoO_CHAR_STRING_SYMBOL,
+            k->words[word_min_id].word
+         );
+         break;
+
+      case ZoO_WORD_HAS_NO_EFFECT:
+         snprintf
+         (
+            *result,
+            sentence_size,
+            " " ZoO_CHAR_STRING_SYMBOL " ",
+            k->words[word_min_id].word
+         );
+         break;
+
+      default:
+         snprintf
+         (
+            *result,
+            sentence_size,
+            " [" ZoO_CHAR_STRING_SYMBOL "] ",
+            k->words[word_min_id].word
+         );
+         break;
+   }
+
+   if ((word_min_score == 0) || (credits == 0))
+   {
+      return 0;
+   }
+
+   --credits;
+
+   /* prevents result [restrict] */
+   *result = extend_left(k, word_min_id, *result, &sentence_size, &credits);
+
+   if (*result == (ZoO_char *) NULL)
+   {
+      return -2;
+   }
+
+   *result = extend_right(k, word_min_id, *result, &sentence_size, &credits);
+
+   if (*result == (ZoO_char *) NULL)
+   {
+      return -2;
+   }
+
+   return 0;
+}
diff --git a/src/core/knowledge.c b/src/core/knowledge.c
new file mode 100644
index 0000000..31ccb97
--- /dev/null
+++ b/src/core/knowledge.c
@@ -0,0 +1,447 @@
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h> /* defines SIZE_MAX */
+
+#include "../io/error.h"
+
+#include "knowledge.h"
+
+/* XXX: are we as close to immutable as we want to be? */
+unsigned int const ZoO_knowledge_punctuation_chars_count = 7;
+const ZoO_char const ZoO_knowledge_punctuation_chars[7] =
+   {
+      '!',
+      ',',
+      '.',
+      ':',
+      ';',
+      '?',
+      '~'
+   };
+
+/* XXX: are we as close to immutable as we want to be? */
+unsigned int const ZoO_knowledge_forbidden_chars_count = 8;
+const ZoO_char const ZoO_knowledge_forbidden_chars[8]=
+   {
+      '(',
+      ')',
+      '[',
+      ']',
+      '{',
+      '}',
+      '<',
+      '>'
+   };
+
+int ZoO_knowledge_find
+(
+   const struct ZoO_knowledge k [const restrict static 1],
+   const ZoO_char word [const restrict static 1],
+   ZoO_index result [const restrict static 1]
+)
+{
+   int cmp;
+   ZoO_index i, current_min, current_max;
+
+   /* This is a binary search. */
+
+   if (k->words_count < 1)
+   {
+      *result = 0;
+
+      return -1;
+   }
+
+   current_min = 0;
+
+   /* overflow-safe: k->words_count >= 1 */
+   current_max = (k->words_count - 1);
+
+   for (;;)
+   {
+      /* FIXME: overflow-safe? */
+      i = ((current_min + current_max) / 2);
+
+      if (i == k->words_count)
+      {
+         *result = k->words_count;
+
+         return -1;
+      }
+
+      cmp =
+         /* XXX: Assumed to be compatible with ZoO_char */
+         strcmp
+         (
+            (char *) word,
+            (const char *) k->words[k->sorted_indices[i]].word
+         );
+
+      if (cmp > 0)
+      {
+         if ((current_min > current_max))
+         {
+            *result = (i + 1);
+
+            return -1;
+         }
+
+         /* FIXME: overflow-safe? */
+         current_min = (i + 1);
+      }
+      else if (cmp < 0)
+      {
+         if ((current_min > current_max) || (i == 0))
+         {
+            *result = i;
+
+            return -1;
+         }
+
+         /* overflow-safe */
+         current_max = (i - 1);
+      }
+      else
+      {
+         *result = k->sorted_indices[i];
+
+         return 0;
+      }
+   }
+}
+
+static void word_init (struct ZoO_knowledge_word w [const restrict static 1])
+{
+   w->word_size = 0;
+   w->word = (ZoO_char *) NULL;
+   w->special = ZoO_WORD_HAS_NO_EFFECT;
+   w->occurrences = 1;
+   w->forward_links_count  = 0;
+   w->backward_links_count = 0;
+   w->forward_links_occurrences  = (ZoO_index *) NULL;
+   w->backward_links_occurrences = (ZoO_index *) NULL;
+   w->forward_links  = (ZoO_index *) NULL;
+   w->backward_links = (ZoO_index *) NULL;
+}
+
+static int add_punctuation_nodes
+(
+   struct ZoO_knowledge k [const static 1]
+)
+{
+   int error;
+   char w[2];
+   ZoO_index i, id;
+
+   if (ZoO_knowledge_learn(k, "START OF LINE", &id) < 0)
+   {
+      ZoO_S_FATAL("Could not add 'START OF LINE' to knowledge.");
+
+      return -2;
+   }
+
+   k->words[id].special = ZoO_WORD_STARTS_SENTENCE;
+   k->words[id].occurrences = 0;
+
+   if (ZoO_knowledge_learn(k, "END OF LINE", &id) < 0)
+   {
+      ZoO_S_FATAL("Could not add 'END OF LINE' to knowledge.");
+
+      return -2;
+   }
+
+   k->words[id].special = ZoO_WORD_ENDS_SENTENCE;
+   k->words[id].occurrences = 0;
+
+   w[1] = '\0';
+
+   error = 0;
+
+   for (i = 0; i < ZoO_knowledge_punctuation_chars_count; ++i)
+   {
+      w[0] = ZoO_knowledge_punctuation_chars[i];
+
+      if (ZoO_knowledge_learn(k, w, &id) < 0)
+      {
+         ZoO_WARNING("Could not add '%s' to knowledge.", w);
+
+         error = -1;
+      }
+      else
+      {
+         k->words[id].special = ZoO_WORD_REMOVES_LEFT_SPACE;
+         k->words[id].occurrences = 0;
+      }
+   }
+
+   return error;
+}
+
+int ZoO_knowledge_initialize (struct ZoO_knowledge k [const static 1])
+{
+   k->words_count = 0;
+   k->words = (struct ZoO_knowledge_word *) NULL;
+   k->sorted_indices = (ZoO_index *) NULL;
+
+   if (add_punctuation_nodes(k) < -1)
+   {
+      ZoO_knowledge_finalize(k);
+
+      return -1;
+   }
+
+   return 0;
+}
+
+static void finalize_word
+(
+   struct ZoO_knowledge_word w [const restrict static 1]
+)
+{
+   if (w->word != (ZoO_char *) NULL)
+   {
+      free((void *) w->word);
+
+      w->word = (ZoO_char *) NULL;
+   }
+
+   if (w->forward_links_occurrences != (ZoO_index *) NULL)
+   {
+      free((void *) w->forward_links_occurrences);
+
+      w->forward_links_occurrences = (ZoO_index *) NULL;
+   }
+
+   if (w->backward_links_occurrences != (ZoO_index *) NULL)
+   {
+      free((void *) w->backward_links_occurrences);
+
+      w->backward_links_occurrences = (ZoO_index *) NULL;
+   }
+
+   if (w->forward_links != (ZoO_index *) NULL)
+   {
+      free((void *) w->forward_links);
+
+      w->forward_links = (ZoO_index *) NULL;
+   }
+
+   if (w->backward_links != (ZoO_index *) NULL)
+   {
+      free((void *) w->backward_links);
+
+      w->backward_links = (ZoO_index *) NULL;
+   }
+
+   w->forward_links_count  = 0;
+   w->backward_links_count = 0;
+}
+
+void ZoO_knowledge_finalize (struct ZoO_knowledge k [const restrict static 1])
+{
+   ZoO_index i;
+
+   for (i = 0; i < k->words_count; ++i)
+   {
+      /* prevents k [restrict] */
+      finalize_word(k->words + i);
+   }
+
+   k->words_count = 0;
+
+   if (k->words != (struct ZoO_knowledge_word *) NULL)
+   {
+      free((void *) k->words);
+
+      k->words = (struct ZoO_knowledge_word *) NULL;
+   }
+
+   if (k->sorted_indices != (ZoO_index *) NULL)
+   {
+      free((void *) k->sorted_indices);
+
+      k->sorted_indices = (ZoO_index *) NULL;
+   }
+}
+
+int ZoO_knowledge_learn
+(
+   struct ZoO_knowledge k [const static 1],
+   const ZoO_char word [const restrict static 1],
+   ZoO_index result [const restrict static 1]
+)
+{
+   struct ZoO_knowledge_word * new_wordlist;
+   ZoO_index * new_sorted_indices;
+   ZoO_index temp;
+
+   /* prevents k [restrict] */
+   if (ZoO_knowledge_find(k, word, result) == 0)
+   {
+      if (k->words[*result].occurrences == ZoO_INDEX_MAX)
+      {
+         ZoO_WARNING
+         (
+            "Maximum number of occurrences has been reached for word '"
+            ZoO_CHAR_STRING_SYMBOL
+            "'.",
+            word
+         );
+
+         return -1;
+      }
+
+      /* overflow-safe */
+      k->words[*result].occurrences += 1;
+
+      return 0;
+   }
+
+   if (k->words_count == ZoO_INDEX_MAX)
+   {
+      ZoO_S_WARNING("Maximum number of words has been reached.");
+
+      return -1;
+   }
+
+   new_wordlist =
+      (struct ZoO_knowledge_word *) realloc
+      (
+         (void *) k->words,
+         (
+            (
+               /* overflow-safe: k->words_count < ZoO_INDEX_MAX */
+               (size_t) (k->words_count + 1)
+            )
+            * sizeof(struct ZoO_knowledge_word)
+         )
+      );
+
+   if (new_wordlist == (struct ZoO_knowledge_word *) NULL)
+   {
+      ZoO_ERROR
+      (
+         "Could not learn the word '%s': unable to realloc the word list.",
+         word
+      );
+
+      return -1;
+   }
+
+   k->words = new_wordlist;
+
+   new_sorted_indices =
+      (ZoO_index *) realloc
+      (
+         (void *) k->sorted_indices,
+         (
+            (
+               /* overflow-safe: k->words_count < ZoO_INDEX_MAX */
+               (size_t) (k->words_count + 1)
+            )
+            * sizeof(ZoO_index)
+         )
+      );
+
+   if (new_sorted_indices == (ZoO_index *) NULL)
+   {
+      ZoO_ERROR
+      (
+         "Could not learn the word '"
+         ZoO_CHAR_STRING_SYMBOL
+         "': unable to realloc the index list.",
+         word
+      );
+
+      return -1;
+   }
+
+   k->sorted_indices = new_sorted_indices;
+
+   /* We can only move indices right of *result if they exist. */
+   if (*result != k->words_count)
+   {
+      /* TODO: check if correct. */
+      memmove
+      (
+         /*
+          * overflow-safe:
+          *  - k->words_count < ZoO_INDEX_MAX
+          *  - (k->sorted_indices + *result + 1) =< k->words_count
+          */
+         (void *) (k->sorted_indices + *result + 1),
+         /* overflow-safe: see above */
+         (const void *) (k->sorted_indices + *result),
+         (
+            (
+               /* overflow-safe: *result < k->words_count */
+               (size_t) (k->words_count - *result)
+            )
+            * sizeof(ZoO_index)
+         )
+      );
+   }
+
+   temp = *result;
+
+   k->sorted_indices[*result] = k->words_count;
+
+   *result = k->words_count;
+
+   word_init(k->words + *result);
+
+   /* XXX: strlen assumed to work with ZoO_char. */
+   k->words[*result].word_size = strlen(word);
+
+   if (k->words[*result].word_size == SIZE_MAX)
+   {
+      ZoO_S_WARNING
+      (
+         "Could not learn word that had a size too big to store in a '\\0' "
+         "terminated string. Chances are, this is but a symptom of the real "
+         "problem."
+      );
+
+      return -1;
+   }
+
+   /* We also need '\0' */
+   k->words[*result].word_size += 1;
+
+   k->words[*result].word =
+      (ZoO_char *) calloc
+      (
+         k->words[*result].word_size,
+         sizeof(ZoO_char)
+      );
+
+   if (k->words[*result].word == (ZoO_char *) NULL)
+   {
+      ZoO_S_ERROR
+      (
+         "Could not learn word due to being unable to allocate the memory to "
+         "store it."
+      );
+
+      k->words[*result].word_size = 0;
+
+      return -1;
+   }
+
+   memcpy(k->words[*result].word, word, k->words[*result].word_size);
+
+   /* Safe: k->words_count < ZoO_INDEX_MAX */
+   k->words_count += 1;
+
+   ZoO_DEBUG
+   (
+      ZoO_DEBUG_LEARNING,
+      "Learned word {'%s', id: %u, rank: %u}",
+      word,
+      *result,
+      temp
+   );
+
+   return 0;
+}
+
diff --git a/src/core/knowledge.h b/src/core/knowledge.h
new file mode 100644
index 0000000..f20cb16
--- /dev/null
+++ b/src/core/knowledge.h
@@ -0,0 +1,42 @@
+#ifndef _ZoO_CORE_KNOWLEDGE_H_
+#define _ZoO_CORE_KNOWLEDGE_H_
+
+#include "../tool/strings_types.h"
+
+#include "knowledge_types.h"
+
+int ZoO_knowledge_initialize (struct ZoO_knowledge k [const static 1]);
+
+void ZoO_knowledge_finalize (struct ZoO_knowledge k [const static 1]);
+
+int ZoO_knowledge_find
+(
+   const struct ZoO_knowledge k [const restrict static 1],
+   const ZoO_char word [const restrict static 1],
+   ZoO_index result [const restrict static 1]
+);
+
+int ZoO_knowledge_learn
+(
+   struct ZoO_knowledge k [const static 1],
+   const ZoO_char word [const restrict static 1],
+   ZoO_index result [const restrict static 1]
+);
+
+int ZoO_knowledge_assimilate
+(
+   struct ZoO_knowledge k [const static 1],
+   struct ZoO_strings string [const restrict static 1],
+   ZoO_index const aliases_count,
+   const char * restrict aliases [const restrict static aliases_count]
+);
+
+int ZoO_knowledge_extend
+(
+   struct ZoO_knowledge k [const static 1],
+   const struct ZoO_strings string [const static 1],
+   int const ignore_first_word,
+   ZoO_char * result [const static 1]
+);
+
+#endif
diff --git a/src/core/knowledge_types.h b/src/core/knowledge_types.h
new file mode 100644
index 0000000..f2e8161
--- /dev/null
+++ b/src/core/knowledge_types.h
@@ -0,0 +1,46 @@
+#ifndef _ZoO_CORE_KNOWLEDGE_TYPES_H_
+#define _ZoO_CORE_KNOWLEDGE_TYPES_H_
+
+#include "../pervasive.h"
+
+#define ZoO_WORD_START_OF_LINE 0
+#define ZoO_WORD_END_OF_LINE   1
+
+/* XXX: are we as close to immutable as we want to be? */
+extern unsigned int const ZoO_knowledge_punctuation_chars_count;
+extern const ZoO_char const ZoO_knowledge_punctuation_chars[7];
+extern unsigned int const ZoO_knowledge_forbidden_chars_count;
+extern const ZoO_char const ZoO_knowledge_forbidden_chars[8];
+
+
+enum ZoO_knowledge_special_effect
+{
+   ZoO_WORD_HAS_NO_EFFECT,
+   ZoO_WORD_ENDS_SENTENCE,
+   ZoO_WORD_STARTS_SENTENCE,
+   ZoO_WORD_REMOVES_LEFT_SPACE,
+   ZoO_WORD_REMOVES_RIGHT_SPACE
+};
+
+struct ZoO_knowledge_word
+{
+   size_t word_size;
+   ZoO_char * word;
+   enum ZoO_knowledge_special_effect special;
+   ZoO_index occurrences;
+   ZoO_index forward_links_count;
+   ZoO_index backward_links_count;
+   ZoO_index * forward_links_occurrences;
+   ZoO_index * backward_links_occurrences;
+   ZoO_index * forward_links;
+   ZoO_index * backward_links;
+};
+
+struct ZoO_knowledge
+{
+   ZoO_index words_count;
+   ZoO_index * sorted_indices;
+   struct ZoO_knowledge_word * words;
+};
+
+#endif
diff --git a/src/core/main.c b/src/core/main.c
new file mode 100644
index 0000000..34233d6
--- /dev/null
+++ b/src/core/main.c
@@ -0,0 +1,296 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
+#include <signal.h>
+
+#include "../tool/strings.h"
+
+#include "../io/error.h"
+#include "../io/parameters.h"
+#include "../io/data_input.h"
+#include "../io/network.h"
+
+
+#include "knowledge.h"
+
+#include "state_types.h"
+
+static int run = 1;
+
+static void request_termination (int const signo)
+{
+   if ((signo == SIGINT) || (signo == SIGTERM))
+   {
+      run = 0;
+   }
+}
+
+static int initialize
+(
+   struct ZoO_state s [const static 1],
+   int const argc,
+   const char * argv [const static argc]
+)
+{
+   ZoO_S_DEBUG(ZoO_DEBUG_PROGRAM_FLOW, "Zero of One is initializing...");
+
+   srand(time(NULL));
+
+   /* prevents s [restrict] */
+   if (ZoO_knowledge_initialize(&(s->knowledge)) < 0)
+   {
+      return -1;
+   }
+
+   if (ZoO_parameters_initialize(&(s->param), argc, argv) < 0)
+   {
+      ZoO_knowledge_finalize(&(s->knowledge));
+
+      return -1;
+   }
+
+   return 0;
+}
+
+static int load_data_file (struct ZoO_state s [const static 1])
+{
+   struct ZoO_data_input input;
+   char * result;
+
+   if (ZoO_data_input_open(&input, s->param.data_filename) < 0)
+   {
+      return -1;
+   }
+
+   while
+   (
+      ZoO_data_input_read_line
+      (
+         &input,
+         ZoO_knowledge_punctuation_chars_count,
+         ZoO_knowledge_punctuation_chars
+      ) == 0
+   )
+   {
+      (void) ZoO_knowledge_assimilate
+      (
+         &(s->knowledge),
+         &(input.string),
+         s->param.aliases_count,
+         s->param.aliases
+      );
+   }
+
+   ZoO_data_input_close(&input);
+
+   return 0;
+}
+
+static int finalize (struct ZoO_state s [const static 1])
+{
+   int error;
+
+   ZoO_S_DEBUG(ZoO_DEBUG_PROGRAM_FLOW, "Zero of One is finalizing...");
+
+   error = 0;
+
+   /* prevents s [restrict] */
+   ZoO_knowledge_finalize(&(s->knowledge));
+
+   return error;
+}
+
+static int network_connect (struct ZoO_state s [const static 1])
+{
+   return
+      ZoO_network_connect
+      (
+         &(s->network),
+         s->param.irc_server_addr,
+         s->param.irc_server_port,
+         s->param.irc_server_channel,
+         s->param.irc_username,
+         s->param.irc_realname,
+         s->param.aliases[0]
+      );
+}
+
+static int should_reply
+(
+   struct ZoO_parameters param [const restrict static 1],
+   struct ZoO_strings string [const restrict static 1],
+   int should_learn [const restrict static 1]
+)
+{
+   ZoO_index i, j;
+
+   for (i = 0; i < param->aliases_count; ++i)
+   {
+      if (ZoO_IS_PREFIX(param->aliases[i], string->words[0]))
+      {
+         *should_learn = 0;
+
+         return 1;
+      }
+
+      for (j = 1; j < string->words_count; ++j)
+      {
+         if (ZoO_IS_PREFIX(param->aliases[i], string->words[j]))
+         {
+            *should_learn = 1;
+
+            return 1;
+         }
+      }
+   }
+
+   *should_learn = 1;
+
+   return (param->reply_rate >= (rand() % 100));
+}
+
+static void handle_message
+(
+   struct ZoO_state s [const static 1],
+   struct ZoO_strings string [const restrict static 1],
+   ssize_t const msg_offset,
+   ssize_t const msg_size
+)
+{
+   ZoO_char * line;
+   int reply, learn;
+
+   if
+   (
+      ZoO_strings_parse
+      (
+         string,
+         (size_t) msg_size,
+         (s->network.msg + msg_offset),
+         ZoO_knowledge_punctuation_chars_count,
+         ZoO_knowledge_punctuation_chars
+      ) < 0
+   )
+   {
+      ZoO_S_DEBUG(ZoO_DEBUG_PROGRAM_FLOW, "Could not dissect msg.");
+
+      return;
+   }
+
+   if (string->words_count == 0)
+   {
+      return;
+   }
+
+   reply = should_reply(&(s->param), string, &learn);
+
+   if
+   (
+      reply
+      &&
+      (
+         ZoO_knowledge_extend
+         (
+            &(s->knowledge),
+            string,
+            !learn,
+            &line
+         ) == 0
+      )
+   )
+   {
+      if (line[0] == ' ')
+      {
+         strcpy((s->network.msg), (line + 1));
+      }
+      else
+      {
+         strcpy((s->network.msg), line);
+      }
+
+      free((void *) line);
+
+      ZoO_network_send(&(s->network));
+   }
+
+   if (learn)
+   {
+      (void) ZoO_knowledge_assimilate
+      (
+         &(s->knowledge),
+         string,
+         s->param.aliases_count,
+         s->param.aliases
+      );
+   }
+}
+
+static int main_loop  (struct ZoO_state s [const static 1])
+{
+   struct ZoO_strings string;
+   ssize_t msg_offset, msg_size;
+
+   msg_offset = 0;
+   msg_size = 0;
+
+   ZoO_strings_initialize(&string);
+
+   while (run)
+   {
+      if (ZoO_network_receive(&(s->network), &msg_offset, &msg_size) == 0)
+      {
+         handle_message(s, &string, msg_offset, msg_size);
+      }
+   }
+
+   ZoO_strings_finalize(&string);
+
+   ZoO_network_disconnect(&(s->network));
+
+   return 0;
+}
+
+int main (int const argc, const char * argv [const static argc])
+{
+   struct ZoO_state s;
+
+   if (initialize(&s, argc, argv) < 0)
+   {
+      return -1;
+   }
+
+   if (load_data_file(&s) < 0)
+   {
+      goto CRASH;
+   }
+
+   if (network_connect(&s) < 0)
+   {
+      goto CRASH;
+   }
+
+   if (main_loop(&s) < 0)
+   {
+      goto CRASH;
+   }
+
+   (void) finalize(&s);
+
+   ZoO_S_DEBUG(ZoO_DEBUG_PROGRAM_FLOW, "Zero of One terminated normally.");
+
+   return 0;
+
+   CRASH:
+   {
+      (void) finalize(&s);
+
+      ZoO_S_DEBUG
+      (
+         ZoO_DEBUG_PROGRAM_FLOW,
+         "Zero of One terminated by crashing."
+      );
+
+      return -1;
+   }
+}
diff --git a/src/core/state_types.h b/src/core/state_types.h
new file mode 100644
index 0000000..89c814e
--- /dev/null
+++ b/src/core/state_types.h
@@ -0,0 +1,16 @@
+#ifndef _ZoO_CORE_STATE_TYPES_H_
+#define _ZoO_CORE_STATE_TYPES_H_
+
+#include "../io/parameters_types.h"
+#include "../io/network_types.h"
+
+#include "knowledge_types.h"
+
+struct ZoO_state
+{
+   struct ZoO_parameters param;
+   struct ZoO_knowledge knowledge;
+   struct ZoO_network network;
+};
+
+#endif
diff --git a/src/io/CMakeLists.txt b/src/io/CMakeLists.txt
new file mode 100644
index 0000000..a13154b
--- /dev/null
+++ b/src/io/CMakeLists.txt
@@ -0,0 +1,8 @@
+set(
+   SRC_FILES ${SRC_FILES}
+   ${CMAKE_CURRENT_SOURCE_DIR}/parameters.c
+   ${CMAKE_CURRENT_SOURCE_DIR}/network.c
+   ${CMAKE_CURRENT_SOURCE_DIR}/data_input.c
+)
+set(SRC_FILES ${SRC_FILES} PARENT_SCOPE)
+
diff --git a/src/io/data_input.c b/src/io/data_input.c
new file mode 100644
index 0000000..e31d33b
--- /dev/null
+++ b/src/io/data_input.c
@@ -0,0 +1,98 @@
+#define _POSIX_C_SOURCE 200809L
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h> /* defines SIZE_MAX */
+
+#include "error.h"
+
+#include "data_input.h"
+
+int ZoO_data_input_open
+(
+   struct ZoO_data_input di [const static 1],
+   const char filename [const restrict static 1]
+)
+{
+   /* prevents di [restrict] */
+   ZoO_strings_initialize(&(di->string));
+
+   di->file = fopen(filename, "r");
+
+   if (di->file == (FILE *) NULL)
+   {
+      ZoO_ERROR
+      (
+         "Could not open file '%s' in readonly mode.",
+         filename
+      );
+
+      return -1;
+   }
+
+   return 0;
+}
+
+int ZoO_data_input_read_line
+(
+   struct ZoO_data_input di [const static 1],
+   ZoO_index const punctuations_count,
+   const ZoO_char punctuations [const restrict static punctuations_count]
+)
+{
+   size_t line_size, i, w_start;
+   ZoO_char * line;
+
+   /* prevents di [restrict] */
+   ZoO_strings_finalize(&(di->string));
+
+   line = (ZoO_char *) NULL;
+   line_size = 0;
+
+   /* XXX: assumed compatible with ZoO_char */
+
+   if (getline(&line, &line_size, di->file) < 1)
+   {
+      free((void *) line);
+
+      return -1;
+   }
+
+   line_size = strlen(line);
+   line[line_size - 1] = '\0';
+
+   --line_size; /* removed '\n' */
+
+   if
+   (
+      ZoO_strings_parse
+      (
+         &(di->string),
+         line_size,
+         line,
+         punctuations_count,
+         punctuations
+      ) < 0
+   )
+   {
+      free((void *) line);
+
+      return -1;
+   }
+
+   free((void *) line);
+
+   return 0;
+}
+
+void ZoO_data_input_close (struct ZoO_data_input di [const static 1])
+{
+   if (di->file != (FILE *) NULL)
+   {
+      fclose(di->file);
+
+      di->file = (FILE *) NULL;
+   }
+
+   /* prevents di [restrict] */
+   ZoO_strings_finalize(&(di->string));
+}
diff --git a/src/io/data_input.h b/src/io/data_input.h
new file mode 100644
index 0000000..a2f004b
--- /dev/null
+++ b/src/io/data_input.h
@@ -0,0 +1,21 @@
+#ifndef _ZoO_IO_DATA_INPUT_H_
+#define _ZoO_IO_DATA_INPUT_H_
+
+#include "data_input_types.h"
+
+int ZoO_data_input_open
+(
+   struct ZoO_data_input di [const static 1],
+   const char filename [const restrict static 1]
+);
+
+int ZoO_data_input_read_line
+(
+   struct ZoO_data_input di [const static 1],
+   ZoO_index const punctuations_count,
+   const ZoO_char punctuations [const restrict static punctuations_count]
+);
+
+void ZoO_data_input_close (struct ZoO_data_input di [const static 1]);
+
+#endif
diff --git a/src/io/data_input_types.h b/src/io/data_input_types.h
new file mode 100644
index 0000000..bd2709b
--- /dev/null
+++ b/src/io/data_input_types.h
@@ -0,0 +1,16 @@
+#ifndef _ZoO_IO_DATA_INPUT_TYPES_H_
+#define _ZoO_IO_DATA_INPUT_TYPES_H_
+
+#include <stdio.h>
+
+#include "../pervasive.h"
+
+#include "../tool/strings.h"
+
+struct ZoO_data_input
+{
+   FILE * restrict file;
+   struct ZoO_strings string;
+};
+
+#endif
diff --git a/src/io/error.h b/src/io/error.h
new file mode 100644
index 0000000..e4267a0
--- /dev/null
+++ b/src/io/error.h
@@ -0,0 +1,146 @@
+#ifndef _ZoO_IO_ERROR_H_
+#define _ZoO_IO_ERROR_H_
+
+#include <stdio.h>
+
+#include "../pervasive.h"
+
+#define ZoO_DEBUG_ALL 1
+
+#ifndef ZoO_DEBUG_ALL
+   #define ZoO_DEBUG_ALL 0
+#endif
+
+#ifndef ZoO_DEBUG_PROGRAM_FLOW
+   #define ZoO_DEBUG_PROGRAM_FLOW   (0 || ZoO_DEBUG_ALL)
+#endif
+
+#ifndef ZoO_DEBUG_CONFIG
+   #define ZoO_DEBUG_CONFIG         (0 || ZoO_DEBUG_ALL)
+#endif
+
+#ifndef ZoO_DEBUG_LEARNING
+   #define ZoO_DEBUG_LEARNING       (0 || ZoO_DEBUG_ALL)
+#endif
+
+#ifndef ZoO_DEBUG_NETWORK
+   #define ZoO_DEBUG_NETWORK        (0 || ZoO_DEBUG_ALL)
+#endif
+
+#define ZoO_ENABLE_WARNINGS_OUTPUT              1
+#define ZoO_ENABLE_RUNTIME_ERRORS_OUTPUT        1
+#define ZoO_ENABLE_PROGRAMMING_ERRORS_OUTPUT    1
+#define ZoO_ENABLE_FATAL_ERROR_OUTPUT           1
+
+#ifdef ZoO_ENABLE_ERROR_LOCATION
+   #define ZoO_LOCATION "[" __FILE__ "][" ZoO_TO_STRING(__LINE__) "]"
+#else
+   #define ZoO_LOCATION ""
+#endif
+
+#define ZoO_PRINT_STDERR(symbol, str, ...)\
+   fprintf(stderr, "[" symbol "]" ZoO_LOCATION " " str "\n", __VA_ARGS__);
+
+/*
+ * Given that we use preprocessor contants as flags, we can expect the compilers
+ * to remove the test condition for disabled flags. No need to be shy about
+ * allowing many debug options.
+ */
+
+#define ZoO_DEBUG(flag, str, ...)\
+   ZoO_ISOLATE\
+   (\
+      if (flag)\
+      {\
+         ZoO_PRINT_STDERR("D", str, __VA_ARGS__);\
+      }\
+   )
+
+
+#define ZoO_WARNING(str, ...)\
+   ZoO_ISOLATE\
+   (\
+      if (ZoO_ENABLE_WARNINGS_OUTPUT)\
+      {\
+         ZoO_PRINT_STDERR("W", str, __VA_ARGS__);\
+      }\
+   )
+
+#define ZoO_ERROR(str, ...)\
+   ZoO_ISOLATE\
+   (\
+      if (ZoO_ENABLE_RUNTIME_ERRORS_OUTPUT)\
+      {\
+         ZoO_PRINT_STDERR("E", str, __VA_ARGS__);\
+      }\
+   )
+
+#define ZoO_PROG_ERROR(str, ...)\
+   ZoO_ISOLATE\
+   (\
+      if (ZoO_ENABLE_PROGRAMMING_ERRORS_OUTPUT)\
+      {\
+         ZoO_PRINT_STDERR("P", str, __VA_ARGS__);\
+      }\
+   )
+
+#define ZoO_FATAL(str, ...)\
+   ZoO_ISOLATE\
+   (\
+     if (ZoO_ENABLE_FATAL_ERROR_OUTPUT)\
+      {\
+         ZoO_PRINT_STDERR("F", str, __VA_ARGS__);\
+      }\
+   )
+
+/* For outputs without dynamic content (static). ******************************/
+
+#define ZoO_PRINT_S_STDERR(symbol, str)\
+   fprintf(stderr, "[" symbol "]" ZoO_LOCATION " " str "\n");
+
+#define ZoO_S_DEBUG(flag, str)\
+   ZoO_ISOLATE\
+   (\
+      if (flag)\
+      {\
+         ZoO_PRINT_S_STDERR("D", str);\
+      }\
+   )
+
+#define ZoO_S_WARNING(str)\
+   ZoO_ISOLATE\
+   (\
+      if (ZoO_ENABLE_WARNINGS_OUTPUT)\
+      {\
+         ZoO_PRINT_S_STDERR("W", str);\
+      }\
+   )
+
+#define ZoO_S_ERROR(str)\
+   ZoO_ISOLATE\
+   (\
+      if (ZoO_ENABLE_RUNTIME_ERRORS_OUTPUT)\
+      {\
+         ZoO_PRINT_S_STDERR("E", str);\
+      }\
+   )
+
+#define ZoO_S_PROG_ERROR(str)\
+   ZoO_ISOLATE\
+   (\
+      if (ZoO_ENABLE_PROGRAMMING_ERRORS_OUTPUT)\
+      {\
+         ZoO_PRINT_S_STDERR("P", str);\
+      }\
+   )
+
+#define ZoO_S_FATAL(str)\
+   ZoO_ISOLATE\
+   (\
+     if (ZoO_ENABLE_FATAL_ERROR_OUTPUT)\
+      {\
+         ZoO_PRINT_S_STDERR("F", str);\
+      }\
+   )
+
+#endif
diff --git a/src/io/network.c b/src/io/network.c
new file mode 100644
index 0000000..c8d05a2
--- /dev/null
+++ b/src/io/network.c
@@ -0,0 +1,483 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+
+/* "POSIX.1  does not require the inclusion of <sys/types.h>" */
+/* - man page for setsockopt */
+/* #include <sys/types.h> */
+#include <sys/socket.h>
+#include <sys/time.h>
+
+#include "error.h"
+
+#include "network.h"
+
+static int reconnect (struct ZoO_network net [const restrict static 1])
+{
+   struct timeval timeout;
+   int old_errno = errno;
+
+   errno = 0;
+   timeout.tv_sec = ZoO_NETWORK_TIMEOUT;
+   timeout.tv_usec = 0;
+
+   if (net->connection != -1)
+   {
+      close(net->connection);
+   }
+
+   net->connection =
+      socket
+      (
+         net->addrinfo->ai_family,
+         net->addrinfo->ai_socktype,
+         net->addrinfo->ai_protocol
+      );
+
+   if (net->connection == -1)
+   {
+      ZoO_FATAL
+      (
+         "Could not create socket: %s.",
+         strerror(errno)
+      );
+
+      errno = old_errno;
+
+      return -1;
+   }
+
+   errno = 0;
+
+   if
+   (
+      (
+         setsockopt
+         (
+            net->connection,
+            SOL_SOCKET,
+            SO_RCVTIMEO,
+            (const void *) &timeout,
+            (socklen_t) sizeof(struct timeval)
+         ) < 0
+      )
+      ||
+      (
+         setsockopt
+         (
+            net->connection,
+            SOL_SOCKET,
+            SO_SNDTIMEO,
+            (const void *) &timeout,
+            (socklen_t) sizeof(struct timeval)
+         ) < 0
+      )
+   )
+   {
+      ZoO_ERROR("Could not set timeout on network socket: %s", strerror(errno));
+
+      errno = old_errno;
+
+      return -1;
+   }
+
+   errno = old_errno;
+
+   ZoO_S_DEBUG(ZoO_DEBUG_NETWORK, "(Re)connecting to network...");
+
+   if
+   (
+      connect
+      (
+         net->connection,
+         net->addrinfo->ai_addr,
+         net->addrinfo->ai_addrlen
+      ) != 0
+   )
+   {
+      ZoO_ERROR
+      (
+         "Unable to connect to the network: %s",
+         strerror(errno)
+      );
+
+      errno = old_errno;
+
+      return -1;
+   }
+
+   errno = old_errno;
+
+   snprintf
+   (
+      net->msg,
+      512,
+      "USER %s 8 * :%s\r\n",
+      net->user,
+      net->name
+   );
+
+   errno = 0;
+
+   if (write(net->connection, net->msg, strlen(net->msg)) < 1)
+   {
+      ZoO_ERROR
+      (
+         "Unable to write to the network: %s",
+         strerror(errno)
+      );
+
+      errno = old_errno;
+
+      return -1;
+   }
+
+   snprintf
+   (
+      net->msg,
+      512,
+      "NICK %s\r\n",
+      net->nick
+   );
+
+   errno = 0;
+
+   if (write(net->connection, net->msg, strlen(net->msg)) < 1)
+   {
+      ZoO_ERROR
+      (
+         "Unable to write to the network: %s",
+         strerror(errno)
+      );
+
+      errno = old_errno;
+
+      return -1;
+   }
+
+   errno = old_errno;
+
+   net->buffer_remaining = 0;
+   net->buffer_index = 0;
+   ZoO_S_DEBUG(ZoO_DEBUG_NETWORK, "(Re)connected.");
+
+   return 0;
+}
+
+int ZoO_network_connect
+(
+   struct ZoO_network net [const static 1],
+   const char host [const restrict static 1],
+   const char port [const restrict static 1],
+   const char channel [const restrict static 1],
+   const char user [const restrict static 1],
+   const char name [const restrict static 1],
+   const char nick [const restrict static 1]
+)
+{
+   int error;
+   struct addrinfo hints;
+   const int old_errno = errno;
+
+   net->connection = -1;
+   net->channel = channel;
+   net->user = user;
+   net->name = name;
+   net->nick = nick;
+   net->buffer_index = 0;
+   net->buffer_remaining = 0;
+
+   memset(&hints, 0, sizeof(struct addrinfo));
+   memset(net->msg, 0, (sizeof(ZoO_char) * 513));
+
+   hints.ai_family = AF_INET;
+   hints.ai_socktype = SOCK_STREAM;
+
+   errno = 0;
+
+   error = getaddrinfo(host, port, &hints, &(net->addrinfo));
+
+   if (error != 0)
+   {
+      if (error == EAI_SYSTEM)
+      {
+         ZoO_ERROR
+         (
+            "Could not retrieve server information: %s.",
+            strerror(errno)
+         );
+      }
+      else
+      {
+         ZoO_FATAL
+         (
+            "Could not retrieve server information: %s.",
+            gai_strerror(error)
+         );
+      }
+
+      errno = old_errno;
+
+      return -1;
+   }
+
+   errno = 0;
+
+
+   reconnect(net);
+
+   return 0;
+}
+
+int ZoO_network_receive
+(
+   struct ZoO_network net [const restrict static 1],
+   size_t msg_offset [const restrict static 1],
+   size_t msg_size [const restrict static 1]
+)
+{
+   int old_errno;
+   ssize_t in_count, in_index, msg_index, cmd;
+
+   old_errno = errno;
+
+   for (;;)
+   {
+      msg_index = 0;
+
+      errno = 0;
+
+      while
+      (
+         (
+            (in_count =
+               read(
+                  net->connection,
+                  (net->buffer + net->buffer_index),
+                  (512 - net->buffer_index)
+               )
+            ) > 0
+         )
+      )
+      {
+         net->buffer_remaining += in_count;
+
+         for
+         (
+            in_index = 0;
+            in_index < net->buffer_remaining;
+            ++in_index
+         )
+         {
+            net->msg[msg_index] = net->buffer[net->buffer_index + in_index];
+
+            if
+            (
+               (msg_index == 511)
+               ||
+               (
+                  (msg_index > 0)
+                  && (net->msg[msg_index - 1] == '\r')
+                  && (net->msg[msg_index] == '\n')
+               )
+            )
+            {
+               net->msg[msg_index + 1] = '\0';
+
+
+               if (net->buffer_index != net->buffer_remaining)
+               {
+                  memmove
+                  (
+                     net->buffer,
+                     (net->buffer + net->buffer_index),
+                     (size_t) net->buffer_remaining
+                  );
+
+                  net->buffer_index = 0;
+               }
+
+               net->buffer_remaining -= (in_index + 1);
+
+               errno = old_errno;
+
+               goto READ_MSG;
+            }
+
+            ++msg_index;
+         }
+
+         net->buffer_remaining = 0;
+         net->buffer_index = 0;
+
+         errno = 0;
+      }
+
+      ZoO_ERROR
+      (
+         "Something went wrong while trying to read from the network: %s.",
+         strerror(errno)
+      );
+
+      errno = old_errno;
+
+      if (reconnect(net) < 0)
+      {
+         return -1;
+      }
+
+      continue;
+
+      READ_MSG:
+
+      ZoO_DEBUG(ZoO_DEBUG_NETWORK, "[NET->in] %s\n", net->msg);
+
+      /* XXX: doesn't that prevent net [restrict]? */
+      if (ZoO_IS_PREFIX("PING", net->msg))
+      {
+         errno = 0;
+
+         net->msg[1] = 'O';
+
+         if (write(net->connection, net->msg, strlen(net->msg)) < 1)
+         {
+            ZoO_ERROR("Could not reply to PING request: %s", strerror(errno));
+
+            errno = old_errno;
+
+            if (reconnect(net) < 0)
+            {
+               return -1;
+            }
+
+            continue;
+         }
+
+         ZoO_DEBUG(ZoO_DEBUG_NETWORK, "[NET->out] %s\n", net->msg);
+
+         errno = old_errno;
+      }
+      else if (net->msg[0] == ':')
+      {
+         cmd = 0;
+
+         for (in_index = 1; in_index < 512; in_index++)
+         {
+            if (net->msg[in_index] == ' ')
+            {
+               cmd = (in_index + 1);
+
+               break;
+            }
+         }
+
+         if (cmd == 0)
+         {
+            continue;
+         }
+
+         if (ZoO_IS_PREFIX("001", (net->msg + cmd)))
+         {
+            snprintf
+            (
+               net->msg,
+               512,
+               "JOIN :%s\r\n",
+               net->channel
+            );
+
+            errno = 0;
+
+            if (write(net->connection, net->msg, strlen(net->msg)) < 1)
+            {
+               ZoO_ERROR
+               (
+                  "Could not send JOIN request: %s",
+                  strerror(errno)
+               );
+
+               errno = old_errno;
+
+               if (reconnect(net) < 0)
+               {
+                  return -1;
+               }
+            }
+
+            ZoO_DEBUG(ZoO_DEBUG_NETWORK, "[NET->out] %s", net->msg);
+
+            continue;
+         }
+
+         if (ZoO_IS_PREFIX("PRIVMSG", (net->msg + cmd)))
+         {
+            for (; in_index < 512; in_index++)
+            {
+               if (net->msg[in_index] == ':')
+               {
+                  cmd = (in_index + 1);
+
+                  break;
+               }
+            }
+
+            *msg_offset = cmd;
+            *msg_size = (msg_index - *msg_offset - 1);
+
+            /*net->msg[*msg_size - 1] = '\0'; */
+
+            return 0;
+         }
+      }
+   }
+}
+
+int ZoO_network_send (struct ZoO_network net [const restrict static 1])
+{
+   int const old_errno = errno;
+
+   snprintf
+   (
+      net->buffer,
+      512,
+      "PRIVMSG %s :%s\r\n",
+      net->channel,
+      net->msg
+   );
+
+   errno = 0;
+
+   if (write(net->connection, net->buffer, strlen(net->buffer)) < 1)
+   {
+      ZoO_ERROR
+      (
+         "Could not send PRIVMSG: %s.",
+         strerror(errno)
+      );
+
+      errno = old_errno;
+
+      if (reconnect(net) < 0)
+      {
+         return -2;
+      }
+      else
+      {
+         return -1;
+      }
+   }
+
+   errno = old_errno;
+
+   ZoO_DEBUG(ZoO_DEBUG_NETWORK, "[NET->out] %s", net->buffer);
+
+   return 0;
+}
+
+void ZoO_network_disconnect (struct ZoO_network net [const restrict static 1])
+{
+   freeaddrinfo(net->addrinfo);
+   close(net->connection);
+}
+
diff --git a/src/io/network.h b/src/io/network.h
new file mode 100644
index 0000000..ac7284a
--- /dev/null
+++ b/src/io/network.h
@@ -0,0 +1,27 @@
+#ifndef _ZoO_IO_NETWORK_H_
+#define _ZoO_IO_NETWORK_H_
+#include "network_types.h"
+
+int ZoO_network_connect
+(
+   struct ZoO_network net [const static 1],
+   const char host [const restrict static 1],
+   const char port [const restrict static 1],
+   const char channel [const restrict static 1],
+   const char user [const restrict static 1],
+   const char name [const restrict static 1],
+   const char nick [const restrict static 1]
+);
+
+int ZoO_network_receive
+(
+   struct ZoO_network net [const static 1],
+   size_t msg_offset [const restrict static 1],
+   size_t msg_size [const restrict static 1]
+);
+
+int ZoO_network_send (struct ZoO_network net [const restrict static 1]);
+
+void ZoO_network_disconnect (struct ZoO_network net [const restrict static 1]);
+
+#endif
diff --git a/src/io/network_types.h b/src/io/network_types.h
new file mode 100644
index 0000000..16c81da
--- /dev/null
+++ b/src/io/network_types.h
@@ -0,0 +1,26 @@
+#ifndef _ZoO_IO_NETWORK_TYPES_H_
+#define _ZoO_IO_NETWORK_TYPES_H_
+
+#define POSIX_C_SOURCE
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
+
+#include "../pervasive.h"
+
+struct ZoO_network
+{
+   size_t buffer_index;
+   size_t buffer_remaining;
+   struct addrinfo * addrinfo;
+   ZoO_char buffer [513];
+   ZoO_char msg [513];
+   int connection;
+   const char * restrict channel;
+   const char * restrict user;
+   const char * restrict name;
+   const char * restrict nick;
+};
+
+#endif
diff --git a/src/io/parameters.c b/src/io/parameters.c
new file mode 100644
index 0000000..0f7d05c
--- /dev/null
+++ b/src/io/parameters.c
@@ -0,0 +1,354 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+
+#include "../pervasive.h"
+
+#include "error.h"
+
+#include "parameters.h"
+
+static void load_default_parameters
+(
+   struct ZoO_parameters param [const restrict static 1]
+)
+{
+   param->data_filename       = ZoO_DEFAULT_DATA_FILENAME;
+
+   param->irc_server_addr     = ZoO_DEFAULT_IRC_SERVER_ADDR;
+   param->irc_server_port     = ZoO_DEFAULT_IRC_SERVER_PORT;
+   param->irc_server_channel  = ZoO_DEFAULT_IRC_SERVER_CHANNEL;
+   param->irc_username        = ZoO_DEFAULT_IRC_USERNAME;
+   param->irc_realname        = ZoO_DEFAULT_IRC_REALNAME;
+
+   param->reply_rate          = ZoO_DEFAULT_REPLY_RATE;
+
+   param->aliases_count = 0;
+   param->aliases = NULL;
+}
+
+static void print_help (const char exec [const restrict static 1])
+{
+   printf
+   (
+      "Usage: %s [option_1 option_2 ...] NICKNAME [ALIAS_1 ALIAS_2 ...] \n"
+      "NICKNAME is used as the IRC nickname value.\n"
+      "If NICKNAME or any ALIAS is found in an event, the program will reply.\n"
+      "\nAvailable options:\n"
+      "   [--data-filename | -df] FILENAME\n"
+      "      Learn content from FILENAME before connecting.\n"
+      "      Default: %s.\n"
+      "   [--irc-server-addr | -isa] IRC_SERVER_ADDR\n"
+      "      Connect to this server address.\n"
+      "      Default: %s.\n"
+      "   [--irc-server-port | -isp] IRC_SERVER_PORT\n"
+      "      Connect to this server port.\n"
+      "      Default: %s.\n"
+      "   [--irc-server-channel | -isc] IRC_SERVER_CHANNEL\n"
+      "      Connect to this server's channel.\n"
+      "      Default: %s.\n"
+      "   [--irc-username | -iu] USERNAME\n"
+      "      Connect using this as 'username' (shown in WHOIS).\n"
+      "      Default: %s.\n"
+      "   [--irc-realname | -ir] REALNAME\n"
+      "      Connect using this as 'realname' (shown in WHOIS).\n"
+      "      Default: %s.\n"
+      "   [--reply-rate | -rr] REPLY_RATE\n"
+      "      Chance to reply to an event (integer, range [0, 100]).\n"
+      "      Default: %d.\n",
+      exec,
+      ZoO_DEFAULT_DATA_FILENAME,
+      ZoO_DEFAULT_IRC_SERVER_ADDR,
+      ZoO_DEFAULT_IRC_SERVER_PORT,
+      ZoO_DEFAULT_IRC_SERVER_CHANNEL,
+      ZoO_DEFAULT_IRC_USERNAME,
+      ZoO_DEFAULT_IRC_REALNAME,
+      ZoO_DEFAULT_REPLY_RATE
+   );
+}
+
+static int parse_string_arg
+(
+   const char * restrict dest [const restrict static 1],
+   int const i,
+   const char * restrict argv [const restrict static 1],
+   int const argc
+)
+{
+   if (i == argc)
+   {
+      ZoO_FATAL
+      (
+         "Missing value for parameter '%s'.",
+         /* Safe: i > 1 */
+         argv[i - 1]
+      );
+
+      return -1;
+   }
+
+   *dest = argv[i];
+
+   return 0;
+}
+
+static int parse_integer_arg
+(
+   int dest [const restrict static 1],
+   int const i,
+   const char * argv [const restrict static 1],
+   int const argc,
+   int const min_val,
+   int const max_val
+)
+{
+   long int result;
+   char * endptr;
+   const int old_errno = errno;
+
+   if (i == argc)
+   {
+      ZoO_FATAL
+      (
+         "Missing value for parameter '%s'.",
+         /* Safe: i > 1 */
+         argv[i - 1]
+      );
+
+      return -1;
+   }
+
+   errno = 0;
+
+   result = strtol(argv[i], &endptr, 10);
+
+   if
+   (
+      (errno != 0)
+      || ((*endptr) == '\n')
+      || (result < min_val)
+      || (result > max_val)
+   )
+   {
+      ZoO_FATAL
+      (
+         "Invalid or missing value for parameter '%s', accepted range is "
+         "[%d, %d] (integer).",
+         /* Safe: i > 1 */
+         argv[i - 1],
+         min_val,
+         max_val
+      );
+
+      errno = old_errno;
+
+      return -1;
+   }
+
+   *dest = (int) result;
+
+   errno = old_errno;
+
+   return 0;
+}
+
+int ZoO_parameters_initialize
+(
+   struct ZoO_parameters param [const restrict static 1],
+   int const argc,
+   const char * argv [const restrict static argc]
+)
+{
+   int i;
+
+   load_default_parameters(param);
+
+   for (i = 1; i < argc; ++i)
+   {
+      if
+      (
+         (strcmp(argv[i], "--data-filename") == 0)
+         || (strcmp(argv[i], "-df") == 0)
+      )
+      {
+         i += 1;
+
+         if
+         (
+            parse_string_arg
+            (
+               &(param->data_filename),
+               i,
+               argv,
+               argc
+            ) < 0
+         )
+         {
+            return -1;
+         }
+      }
+      else if
+      (
+         (strcmp(argv[i], "--irc-server-addr") == 0)
+         || (strcmp(argv[i], "-isa") == 0)
+      )
+      {
+         i += 1;
+
+         if
+         (
+            parse_string_arg
+            (
+               &(param->irc_server_addr),
+               i,
+               argv,
+               argc
+            ) < 0
+         )
+         {
+            return -1;
+         }
+      }
+      else if
+      (
+         (strcmp(argv[i], "--irc-server-port") == 0)
+         || (strcmp(argv[i], "-isp") == 0)
+      )
+      {
+         i += 1;
+
+         if
+         (
+            parse_string_arg
+            (
+               &(param->irc_server_port),
+               i,
+               argv,
+               argc
+            ) < 0
+         )
+         {
+            return -1;
+         }
+      }
+      else if
+      (
+         (strcmp(argv[i], "--irc-server-channel") == 0)
+         || (strcmp(argv[i], "-isc") == 0)
+      )
+      {
+         i += 1;
+
+         if
+         (
+            parse_string_arg
+            (
+               &(param->irc_server_channel),
+               i,
+               argv,
+               argc
+            ) < 0
+         )
+         {
+            return -1;
+         }
+      }
+      else if
+      (
+         (strcmp(argv[i], "--irc-username") == 0)
+         || (strcmp(argv[i], "-iu") == 0)
+      )
+      {
+         i += 1;
+
+         if
+         (
+            parse_string_arg
+            (
+               &(param->irc_username),
+               i,
+               argv,
+               argc
+            ) < 0
+         )
+         {
+            return -1;
+         }
+      }
+      else if
+      (
+         (strcmp(argv[i], "--irc-realname") == 0)
+         || (strcmp(argv[i], "-in") == 0)
+      )
+      {
+         i += 1;
+
+         if
+         (
+            parse_string_arg
+            (
+               &(param->irc_realname),
+               i,
+               argv,
+               argc
+            ) < 0
+         )
+         {
+            return -1;
+         }
+      }
+      else if
+      (
+         (strcmp(argv[i], "--reply-rate") == 0)
+         || (strcmp(argv[i], "-rr") == 0)
+      )
+      {
+         i += 1;
+
+         if
+         (
+            parse_integer_arg
+            (
+               &(param->reply_rate),
+               i,
+               argv,
+               argc,
+               0,
+               100
+            ) < 0
+         )
+         {
+            return -1;
+         }
+      }
+      else if
+      (
+         (strcmp(argv[i], "--help") == 0)
+         || (strcmp(argv[i], "-h") == 0)
+      )
+      {
+         print_help(argv[0]);
+
+         return 0;
+      }
+      else
+      {
+         break;
+      }
+   }
+
+   if (i == argc)
+   {
+      ZoO_S_FATAL("Missing argument: NICKNAME");
+
+      print_help(argv[0]);
+
+      return -1;
+   }
+
+   param->aliases_count = (argc - i);
+   param->aliases = (argv + i);
+
+   return 1;
+}
diff --git a/src/io/parameters.h b/src/io/parameters.h
new file mode 100644
index 0000000..1011e2b
--- /dev/null
+++ b/src/io/parameters.h
@@ -0,0 +1,13 @@
+#ifndef _ZoO_IO_PARAMETERS_H_
+#define _ZoO_IO_PARAMETERS_H_
+
+#include "parameters_types.h"
+
+int ZoO_parameters_initialize
+(
+   struct ZoO_parameters param [const static 1],
+   int const argc,
+   const char * argv [const static argc]
+);
+
+#endif
diff --git a/src/io/parameters_types.h b/src/io/parameters_types.h
new file mode 100644
index 0000000..6d511d8
--- /dev/null
+++ b/src/io/parameters_types.h
@@ -0,0 +1,20 @@
+#ifndef _ZoO_IO_PARAMETERS_TYPES_H_
+#define _ZoO_IO_PARAMETERS_TYPES_H_
+
+struct ZoO_parameters
+{
+   const char * restrict data_filename;
+
+   const char * restrict irc_server_addr;
+   const char * restrict irc_server_port;
+   const char * restrict irc_server_channel;
+   const char * restrict irc_username;
+   const char * restrict irc_realname;
+
+   int reply_rate;
+
+   int aliases_count;
+   const char * restrict * restrict aliases;
+};
+
+#endif
diff --git a/src/pervasive.h b/src/pervasive.h
new file mode 100644
index 0000000..d2b0344
--- /dev/null
+++ b/src/pervasive.h
@@ -0,0 +1,59 @@
+#ifndef _ZoO_PERVASIVE_H_
+#define _ZoO_PERVASIVE_H_
+
+#include <limits.h>
+
+#ifndef ZoO_NETWORK_TIMEOUT
+   #define ZoO_NETWORK_TIMEOUT            200
+#endif
+
+#ifndef ZoO_MAX_REPLY_WORDS
+   #define ZoO_MAX_REPLY_WORDS            64
+#endif
+
+#ifndef ZoO_DEFAULT_DATA_FILENAME
+   #define ZoO_DEFAULT_DATA_FILENAME      "./memory.txt"
+#endif
+
+#ifndef ZoO_DEFAULT_IRC_SERVER_ADDR
+   #define ZoO_DEFAULT_IRC_SERVER_ADDR    "irc.foonetic.net"
+#endif
+
+#ifndef ZoO_DEFAULT_IRC_SERVER_PORT
+   #define ZoO_DEFAULT_IRC_SERVER_PORT    "6667"
+#endif
+
+#ifndef ZoO_DEFAULT_IRC_SERVER_CHANNEL
+   #define ZoO_DEFAULT_IRC_SERVER_CHANNEL "#theborghivemind"
+#endif
+
+#ifndef ZoO_DEFAULT_IRC_USERNAME
+   #define ZoO_DEFAULT_IRC_USERNAME       "zeroofone"
+#endif
+
+#ifndef ZoO_DEFAULT_IRC_REALNAME
+   #define ZoO_DEFAULT_IRC_REALNAME       "Zero of One (bot)"
+#endif
+
+#ifndef ZoO_DEFAULT_REPLY_RATE
+   #define ZoO_DEFAULT_REPLY_RATE         8
+#endif
+
+typedef unsigned int ZoO_index;
+#define ZoO_INDEX_MAX UINT_MAX
+
+/* ZoO_char = UTF-8 char */
+typedef char ZoO_char;
+/* Functions that can handle UTF-8 'char' will use this symbol. */
+#define ZoO_CHAR_STRING_SYMBOL "%s"
+
+#define ZoO__TO_STRING(x) #x
+#define ZoO_TO_STRING(x) ZoO__TO_STRING(x)
+#define ZoO_ISOLATE(a) do {a} while (0)
+
+/* strncmp stops at '\0' and strlen does not count '\0'. */
+#define ZoO_IS_PREFIX(a, b) (strncmp(a, b, strlen(a)) == 0)
+
+#define ZoO_STRING_EQUALS(a, b) (strcmp(a, b) == 0)
+
+#endif
diff --git a/src/tool/CMakeLists.txt b/src/tool/CMakeLists.txt
new file mode 100644
index 0000000..3a1d947
--- /dev/null
+++ b/src/tool/CMakeLists.txt
@@ -0,0 +1,7 @@
+set(
+   SRC_FILES ${SRC_FILES}
+   ${CMAKE_CURRENT_SOURCE_DIR}/strings.c
+)
+
+set(SRC_FILES ${SRC_FILES} PARENT_SCOPE)
+
diff --git a/src/tool/strings.c b/src/tool/strings.c
new file mode 100644
index 0000000..fc4434a
--- /dev/null
+++ b/src/tool/strings.c
@@ -0,0 +1,280 @@
+#define _POSIX_C_SOURCE 200809L
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h> /* defines SIZE_MAX */
+
+#include "../io/error.h"
+
+#include "strings.h"
+
+
+void ZoO_strings_initialize (struct ZoO_strings s [const restrict static 1])
+{
+   s->words_count = 0;
+   s->words = (ZoO_char **) NULL;
+   s->word_sizes = (size_t *) NULL;
+}
+
+void ZoO_strings_finalize (struct ZoO_strings s [const restrict static 1])
+{
+   if (s->words_count != 0)
+   {
+      ZoO_index i;
+
+      for (i = 0; i < s->words_count; ++i)
+      {
+         free((void *) s->words[i]);
+      }
+
+      s->words_count = 0;
+
+      free((void *) s->words);
+      free((void *) s->word_sizes);
+
+      s->words = (ZoO_char **) NULL;
+      s->word_sizes = (size_t *) NULL;
+   }
+}
+
+static int add_word
+(
+   struct ZoO_strings s [const restrict static 1],
+   size_t const line_size,
+   const ZoO_char line [const restrict static line_size]
+)
+{
+   size_t * new_s_word_sizes;
+   ZoO_char * new_word, ** new_s_words;
+
+   if (s->words_count == ZoO_INDEX_MAX)
+   {
+      ZoO_S_WARNING("Data input sentence has too many words.");
+
+      return -1;
+   }
+
+   /* overflow-safe, as line_size < SIZE_MAX */
+   new_word = (ZoO_char *) calloc((line_size + 1), sizeof(ZoO_char));
+
+   if (new_word == (ZoO_char *) NULL)
+   {
+      ZoO_S_WARNING("Unable to allocate memory to extract new word.");
+
+      return -1;
+   }
+
+   memcpy((void *) new_word, (const void *) line, line_size);
+
+   new_word[line_size] = '\0';
+
+   new_s_words =
+      (ZoO_char **) realloc
+      (
+         (void *) s->words,
+         /* XXX: (sizeof() * _) assumed overflow-safe. */
+         /* (di->words_count + 1) overflow-safe */
+         (sizeof(ZoO_char *) * (s->words_count + 1))
+      );
+
+   if (new_s_words == (ZoO_char **) NULL)
+   {
+      ZoO_S_WARNING("Unable to reallocate memory to extract new word.");
+
+      free((void *) new_word);
+
+      return -1;
+   }
+
+   s->words = new_s_words;
+
+   new_s_word_sizes =
+      (size_t *) realloc
+      (
+         (void *) s->word_sizes,
+         /* XXX: (sizeof() * _) assumed overflow-safe. */
+         /* (di->words_count + 1) overflow-safe */
+         (sizeof(size_t) * (s->words_count + 1))
+      );
+
+   if (new_s_word_sizes == (size_t *) NULL)
+   {
+      ZoO_S_WARNING("Unable to reallocate memory to extract new word.");
+
+      free((void *) new_word);
+
+      return -1;
+   }
+
+   s->word_sizes = new_s_word_sizes;
+
+   s->words[s->words_count] = new_word;
+   s->word_sizes[s->words_count] = (line_size + 1);
+
+   s->words_count += 1;
+
+   return 0;
+}
+
+static int parse_word
+(
+   struct ZoO_strings s [const restrict static 1],
+   ZoO_index const punctuations_count,
+   const ZoO_char punctuations [const restrict static punctuations_count],
+   size_t const line_size,
+   ZoO_char line [const static line_size]
+)
+{
+   ZoO_index j;
+
+   if (line_size == 0)
+   {
+      return 0;
+   }
+
+   for (j = 0; j < line_size; ++j)
+   {
+      switch (line[j])
+      {
+         case 'A':
+         case 'B':
+         case 'C':
+         case 'D':
+         case 'E':
+         case 'F':
+         case 'G':
+         case 'H':
+         case 'I':
+         case 'J':
+         case 'K':
+         case 'L':
+         case 'M':
+         case 'N':
+         case 'O':
+         case 'P':
+         case 'Q':
+         case 'R':
+         case 'S':
+         case 'T':
+         case 'U':
+         case 'V':
+         case 'W':
+         case 'X':
+         case 'Y':
+         case 'Z':
+            line[j] = 'z' - ('Z' - line[j]);
+            break;
+
+         default:
+            break;
+      }
+   }
+
+   for (j = 0; j < punctuations_count; ++j)
+   {
+      /* overflow-safe: line_size > 1 */
+      if (line[line_size - 1] == punctuations[j])
+      {
+         if (line_size > 1)
+         {
+            if
+            (
+               /* overflow-safe: line_size > 1 */
+               (add_word(s, (line_size - 1), line) < 0)
+               /* overflow-safe: line_size > 1 */
+               /* prevents line[restrict] */
+               || (add_word(s, 1, (line + (line_size - 1))) < 0)
+            )
+            {
+               return -1;
+            }
+
+            return 0;
+         }
+      }
+   }
+
+   return add_word(s, line_size, line);
+}
+
+int ZoO_strings_parse
+(
+   struct ZoO_strings s [const restrict static 1],
+   size_t const input_size,
+   ZoO_char input [const restrict],
+   ZoO_index const punctuations_count,
+   const ZoO_char punctuations [const restrict static punctuations_count]
+)
+{
+   size_t i, w_start;
+
+   ZoO_strings_finalize(s);
+
+   if (input == NULL)
+   {
+      return 0;
+   }
+
+   i = 0;
+
+   /* overflow-safe: input is '\0' terminated. */
+   while (input[i] == ' ')
+   {
+      ++i;
+   }
+
+   w_start = i;
+
+   for (; i < input_size; ++i)
+   {
+      if (input[i] == ' ')
+      {
+         if
+         (
+            parse_word
+            (
+               s,
+               punctuations_count,
+               punctuations,
+               /* overflow-safe: w_start < i */
+               (i - w_start),
+               (input + w_start)
+            ) < 0
+         )
+         {
+            ZoO_strings_finalize(s);
+
+            return -1;
+         }
+
+         ++i;
+
+         /* safe, as input is terminated by '\0' */
+         while (input[i] == ' ')
+         {
+            ++i;
+         }
+
+         w_start = i;
+      }
+   }
+
+   if
+   (
+      parse_word
+      (
+         s,
+         punctuations_count,
+         punctuations,
+         /* overflow-safe: w_start < i */
+         (i - w_start),
+         (input + w_start)
+      ) < 0
+   )
+   {
+      ZoO_strings_finalize(s);
+
+      return -1;
+   }
+
+   return 0;
+}
diff --git a/src/tool/strings.h b/src/tool/strings.h
new file mode 100644
index 0000000..6e6e211
--- /dev/null
+++ b/src/tool/strings.h
@@ -0,0 +1,19 @@
+#ifndef _ZoO_TOOL_STRINGS_H_
+#define _ZoO_TOOL_STRINGS_H_
+
+#include "strings_types.h"
+
+void ZoO_strings_initialize (struct ZoO_strings s [const restrict static 1]);
+
+void ZoO_strings_finalize (struct ZoO_strings s [const restrict static 1]);
+
+int ZoO_strings_parse
+(
+   struct ZoO_strings s [const static 1],
+   size_t const input_size,
+   ZoO_char input [const restrict],
+   ZoO_index const punctuations_count,
+   const ZoO_char punctuations [const restrict static punctuations_count]
+);
+
+#endif
diff --git a/src/tool/strings_types.h b/src/tool/strings_types.h
new file mode 100644
index 0000000..f74dcc8
--- /dev/null
+++ b/src/tool/strings_types.h
@@ -0,0 +1,15 @@
+#ifndef _ZoO_TOOL_STRINGS_TYPES_H_
+#define _ZoO_TOOL_STRINGS_TYPES_H_
+
+#include <stdio.h>
+
+#include "../pervasive.h"
+
+struct ZoO_strings
+{
+   ZoO_index words_count;
+   ZoO_char * restrict * restrict words;
+   size_t * restrict word_sizes;
+};
+
+#endif