rudus/assets/test_prelude.ld

& & the very base: know something's type
& fn type {
& 	"Returns a keyword representing the type of the value passed in."
& 	(x) -> base :type (x)
& }

& & some helper type functions
& fn coll? {
& 	"Returns true if a value is a collection: dict, list, tuple, or set."
& 	(coll as :dict) -> true
& 	(coll as :list) -> true
& 	(coll as :tuple) -> true
& 	& (coll as :set) -> true
& 	(_) -> false
& }

& fn ordered? {
& 	"Returns true if a value is an indexed collection: list or tuple."
& 	(coll as :list) -> true
& 	(coll as :tuple) -> true
& 	(coll as :string) -> true
& 	(_) -> false
& }

& fn assoc? {
& 	"Returns true if a value is an associative collection: a dict or a pkg."
& 	(d as :dict) -> true
& 	(_) -> false
& }

& &&& nil: working with nothing

& fn nil? {
& 	"Returns true if a value is nil."
& 	(nil) -> true
& 	(_) -> false
& }

& fn some? {
& 	"Returns true if a value is not nil."
& 	(nil) -> false
& 	(_) -> true
& }

& fn some {
& 	"Takes a possibly nil value and a default value. Returns the value if it's not nil, returns the default if it's nil."
& 	(nil, default) -> default
& 	(value, _) -> value 
& }

& & ...and if two things are the same
& fn eq? {
& 	"Returns true if all arguments have the same value."
& 	(x) -> true
& 	(x, y) -> base :eq? (x, y)
& 	(x, y, ...zs) -> if eq? (x, y)
& 		then loop (y, zs) with {
& 			(a, []) -> eq? (a, x)
& 			(a, [b, ...cs]) -> if eq? (a, x)
& 				then recur (b, cs)
& 				else false
& 			}
& 		else false
& }

& &&& true & false: boolean logic (part the first)
& fn bool? {
& 	"Returns true if a value is of type :boolean."
& 	(false) -> true
& 	(true) -> true
& 	(_) -> false
& }

& fn true? {
& 	"Returns true if a value is boolean `true`. Useful to distinguish between `true` and anything else."
& 	(true) -> true
& 	(_) -> false
& }

& fn false? {
& 	"Returns `true` if a value is `false`, otherwise returns `false`. Useful to distinguish between `false` and `nil`."
& 	(false) -> true
& 	(_) -> false
& }

& fn bool {
& 	"Returns false if a value is nil or false, otherwise returns true."
& 	(nil) -> false
& 	(false) -> false
& 	(_) -> true
& }

& fn not {
& 	"Returns false if a value is truthy, true if a value is falsy."
& 	(nil) -> true
& 	(false) -> true
& 	(_) -> false
& }

& & tuples: not a lot you can do with them functionally
& fn tuple? {
& 	"Returns true if a value is a tuple."
& 	(tuple as :tuple) -> true
& 	(_) -> false
& }

& &&& functions: getting things done
& fn fn? {
& 	"Returns true if an argument is a function."
& 	(f as :fn) -> true
& 	(_) -> false
& }

& what we need for some very basic list manipulation 
fn first {
  "Retrieves the first element of an ordered collection--a tuple or a list. If the collection is empty, returns nil."
  ([]) -> nil
  (()) -> nil
  ("") -> nil
  (xs as :list) -> base :first (xs)
  (xs as :tuple) -> base :first (xs)
  (str as :string) -> base :slice (str, 0, 1)
}

fn rest {
	"Returns all but the first element of a list or tuple, as a list."
	([]) -> []
	(()) -> ()
	(xs as :list) -> base :rest (xs)
	(xs as :tuple) -> base :rest (xs)
	(str as :string) -> base :rest (str)
}

fn inc {
	"Increments a number."
	(x as :number) -> base :inc (x)
}

& fn dec {
& 	"Decrements a number."
& 	(x as :number) -> base :dec (x)
& }

& fn count {
& 	"Returns the number of elements in a collection (including string)."
& 	(xs as :list) -> base :count (xs)
& 	(xs as :tuple) -> base :count (xs)
& 	(xs as :dict) -> base :count (xs)
& 	(xs as :string) -> base :count (xs)
& 	& (xs as :set) -> base :count (xs)
& }

& fn empty? {
& 	"Returns true if something is empty. Otherwise returns false (including for things that can't logically be empty, like numbers)."
& 	([]) -> true
& 	(#{}) -> true
& 	& (s as :set) -> eq? (s, ${})
& 	(()) -> true
& 	("") -> true
& 	(_) -> false
& }

& fn any? {
& 	"Returns true if something is not empty, otherwise returns false (including for things that can't be logically full, like numbers)."
& 	([...]) -> true
& 	(#{...}) -> true
& 	& (s as :set) -> not (empty? (s))
& 	((...)) -> true
& 	(s as :string) -> not (empty? (s))
& 	(_) -> false
& }

& fn list? {
& 	"Returns true if the value is a list."
& 	(l as :list) -> true
& 	(_) -> false
& }

& fn list {
& 	"Takes a value and returns it as a list. For values, it simply wraps them in a list. For collections, conversions are as follows. A tuple->list conversion preservers order and length. Unordered collections do not preserve order: sets and dicts don't have predictable or stable ordering in output. Dicts return lists of (key, value) tuples."
& 	(x) -> base :list (x)
& }

fn append {
	"Adds an element to a list."
	() -> []
	(xs as :list) -> xs
	(xs as :list, x) -> base :append (xs, x)
}

fn fold {
	"Folds a list."
	(f as :fn, []) -> []
	(f as :fn, xs as :list) -> fold (f, xs, f ())
	(f as :fn, [], root) -> []
	(f as :fn, xs as :list, root) -> loop (root, first (xs), rest (xs)) with {
		(prev, curr, []) -> f (prev, curr)
		(prev, curr, remaining) -> recur (
			f (prev, curr)
			first (remaining)
			rest (remaining)
		)
	}
}

fn map {
	"Maps a function over a list: returns a new list with elements that are the result of applying the function to each element in the original list. E.g., `map ([1, 2, 3], inc) &=> [2, 3, 4]`. With one argument, returns a function that is a mapper over lists; with two, it executes the mapping function right away."
	& (f as :fn) -> map (f, _)
	& (kw as :keyword) -> map (kw, _)
	(f as :fn, xs) -> {
		fn mapper (prev, curr) -> append (prev, f (curr))
		fold (mapper, xs, [])
	}
	& (kw as :keyword, xs) -> {
	& 	fn mapper (prev, curr) -> append (prev, kw (curr))
	& 	fold (mapper, xs, [])
	& }
}

#{
 &  type
 &  coll?
 &  ordered?
 &  assoc?
 &  nil?
 &  some?
 &  some
 &  eq?
 &  bool?
 &  true?
 &  false?
 &  bool
 &  not
 &  tuple?
 &  fn?
 &  rest
  inc
 &  dec
 &  count
 &  empty?
 &  any?
 &  list?
 &  list
 &  first
	& fold
	& append
	map
}