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diff --git a/content/learn/09.lambdas/default.md b/content/learn/09.lambdas/default.md new file mode 100644 index 0000000..a2e6c24 --- /dev/null +++ b/content/learn/09.lambdas/default.md @@ -0,0 +1,366 @@ +--- +menuTitle: Lambda Functions +title: "Lambda Functions" +weight: 9 +--- +In [the previous step](/learn/collections), we added collections, which made +having large amounts of data possible. We also ended up with a really ugly file, +`smithy.fate`, which had way too much code to be readable. We'll start by +removing the label generation sequences. Instead, we'll use lambda functions. + +A lambda function is computation description that can be stored for later use. +It can also take parameters. Since it's a computation, it cannot alter the +memory by itself, nor can it contain any instructions. + +**smithy.fate:** + + (fate_version 1) + + (require smithy_inventory.fate) + + (global (lambda text ((cons weapon int))) get_weapon_offer_label) + (global (lambda text ((cons armor int))) get_armor_offer_label) + + (set get_weapon_offer_label + (lambda + ( ((cons weapon int) offer) ) + (let + ( + (weapon (car offer)) + (price (cdr offer)) + ) + (text + Buy "(var weapon.name)" \(attack: (var weapon.attack), + precision: (var weapon.precision)\) for (var price) coins. + ) + ) + ) + ) + + (set get_armor_offer_label + (lambda + ( ((cons armor int) offer) ) + (let + ( + (armor (car offer)) + (price (cdr offer)) + ) + (text + Buy "(var armor.name)" \(defense: (var armor.defense)\), + for (var price) coins. + ) + ) + ) + ) + + (define_sequence visit_smithy () + ;; This thing is going to show up every time, which isn't great. + As you approach the smithy, you notice that no one's there. All the + wares are out for selling. It's almost as if this story didn't need + more examples of lengthy dialogues. + (newline) + ;; We'll want to start here the next time we enter this sequence. + You have (var hero.money) coins. + (newline) + What will you look at? + (player_choice + ( + ( Let's see the weapons ) + (jump_to see_weapons) + ) + ( + ( Let's see the armors ) + (jump_to see_armors) + ) + ( + ( Nothing, let's go back to the bar ) + ) + ) + ) + + (define_sequence see_weapons () + ;; Still can be improved. + (player_choice + ( + ( (eval get_weapon_offer_label (access smithy_weapons 0)) ) + (visit buy_weapon (access smithy_weapons 0)) + (jump_to visit_smithy) + ) + ( + ( (eval get_weapon_offer_label (access smithy_weapons 1)) ) + (visit buy_weapon (access smithy_weapons 1)) + (jump_to visit_smithy) + ) + ( + ( Nevermind ) + (jump_to visit_smithy) + ) + ) + ) + + (define_sequence see_armors () + ;; Still can be improved. + (player_choice + ( + ( (eval get_armor_offer_label (access smithy_armors 0)) ) + (visit buy_armor (access smithy_armors 0)) + (jump_to visit_smithy) + ) + ( + ( (eval get_armor_offer_label (access smithy_armors 1)) ) + (visit buy_armor (access smithy_armors 1)) + (jump_to visit_smithy) + ) + ( + ( Nevermind ) + (jump_to visit_smithy) + ) + ) + ) + + (define_sequence buy_weapon ( ((cons weapon int) weapon) ) + ;; We can't even deny a sell yet... + (set hero.weapon (car weapon)) + Equipped (var hero.weapon.name). + (newline) + ) + + (define_sequence buy_armor ( ((cons armor int) armor) ) + ;; We can't even deny a sell yet... + (set hero.armor (car armor)) + Equipped (var hero.armor.name). + (newline) + ) + +* `(lambda return_type (param_type0 param_type1 ...))` is the type corresponding + to a lambda function returning a value of type `return_type` and taking as + parameters values of types `param_type0`, `param_type1`, ... +* `(eval variable_name param0 param1 ...)` computes and returns the result of + the lambda function stored in `variable_name` by giving it as parameter the + values `param0`, `param1`, ... +* `(let ( (name0 val0) ... ) computation)` computes and returns `computation` as + if `name0` was a defined variable of value `val0`. + +Lambda functions are *very* useful. They can be used to manipulate lists in many +ways. They can also be used to abstract away some complicated computation. + +This was a first step toward cleaning up `smithy.fate`. Next, we'll use +[conditions](/learn/conditions) to improve things further. + +---- + +## Unchanged Files + +**data.fate:** + + (fate_version 1) + + (declare_structure weapon + (text name) + (int attack) + (int precision) + ) + + (declare_structure armor + (text name) + (int defense) + ) + + (declare_structure character + (string name) + (int money) + (weapon weapon) + (armor armor) + ) + + (global character hero) + + (set_fields! hero.weapon + (name (text "Legendary" sword)) + (attack 3) + (precision 50) + ) + + (set_fields! hero.armor + (name (text "Refined" attire)) + (defense 1) + ) + + (set hero.money 42) + +**get_a_refill.fate:** + + (fate_version 1) + + (require data.fate) + (require actions.fate) + + (define_sequence lower_price_of_booze + ( + ((ptr int) price_pointer) + (int decrease) + ) + Great! The price of booze just lowered from (at price_pointer) + (set (at price_pointer) + (- + (at price_pointer) + (var decrease) + ) + ) + to (at price_pointer)! + ) + + (define_sequence get_a_refill () + (local int price_of_booze) + + (set price_of_booze 12) + + Staring straight at the barman, you raise your glass and proclaim: + (newline) + "This soon-to-be world savior needs more booze!" + (newline) + The barman's lack of reaction is disappointing, but seeing the beer + being poured does help improve the mood. + (newline) + Satisfied, you hand the barman (var price_of_booze) copper coins. + (visit pay (var price_of_booze)) + (newline) + The barman sighs, then asks: + (prompt_string (ptr hero.name) 2 64 What is your name, then, hero?) + (var hero.name)? + (newline) + The barman looks surprised. + (newline) + (visit lower_price_of_booze (ptr price_of_booze) 4) + (newline) + "I have heard of you, (var hero.name)," the barman exclaims, "I have + a quest for you!" + (newline) + It's your turn to sigh. + (newline) + The barman hands you a bag, and says: + (newline) + "Take this pre-payment and head to the smithy." + (newline) + ) + +**actions.fate:** + + (fate_version 1) + + (require data.fate) + + (define_sequence pay ( (int cost) ) + (set hero_money + (- (var hero.money) (var cost)) + ) + ) + +**falling_asleep.fate:** + + (fate_version 1) + + (require data.fate) + + (define_sequence fall_asleep () + Deciding to break away from the expected storyline, you promptly + fall asleep. + (newline) + ... + (newline) + Upon waking up, your hard-trained reflexes inform you that someone + stole all your money. + (set hero.money 0) + (newline) + This set-back was more than you could take. You give up on this + barely coherent story. + (end) + ) + +**main.fate:** + + (fate_version 1) + + Once upon a time, starting a story with these words wasn't considered + a cliche. Starting in a tavern might also not be seen as very + original. Having the main character be an street orphan, raised by + some mysterious sage all to end up as a mercenary with an uncommonly + strong sense of honor probably isn't going to lead to any praises for + novelty either. Maybe you should drink to that. + (newline) + Or maybe you shouldn't. This isn't your first mug. Not your second + either. Drinking to forget that you are a stereotypical hero isn't + going to solve anything. Worse, the alcoholic trait is part of the + image. + (newline) + As you contemplate your own pointless description, your gaze leaves + what turns out to be an already empty glass in your hand and finds the + barman. + + (player_choice + ( + ( Ask the barman for a refill ) + (visit get_a_refill) + ) + ( + ( Fall asleep ) + (jump_to fall_asleep) + ) + ) + + (require get_a_refill.fate) + (require falling_asleep.fate) + + (end) + +**smithy_inventory.fate:** + (fate_version 1) + + (require data.fate) + + (global (list (cons weapon int)) smithy_weapons) + (global (list (cons weapon int)) smithy_armors) + + (add! + (cons + (set_fields (default weapon) + (name (text An Iron Rod)) + (attack 10) + (precision 70) + ) + 176 + ) + smithy_weapons + ) + (add! + (cons + (set_fields (default weapon) + (name (text A Magnificient Brick)) + (attack 6) + (precision 90) + ) + 110 + ) + smithy_weapons + ) + + (add! + (cons + (set_fields (default armor) + (name (text A raincoat?!)) + (defense 7) + ) + 160 + ) + smithy_armors + ) + (add! + (cons + (set_fields (default armor) + (name (text A nice cape)) + (defense 3) + ) + 50 + ) + smithy_armors + ) |