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Anonymous_functions.fold
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Anonymous_functions.fold
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--
-- # Anonymous Functions
--
-- Simple lambda functions.
x -> x
x -> x + x
-- Lambda function with a block.
x ->
let a = x + x in
a + 1
f x y ==> (f x) y
f(x, y)
-- Apply a transformation using a lambda.
List.map (should_print_output value db_handler -> x * x) [1..10]
List.map (fn should_print_output value db_handler -> x * x) [1..10]
List.map (lambda should_print_output value db_handler -> x * x) [1..10]
def prod x = x * x
List.map prod [1..10]
--
List.map {
| 0 -> 0
| n if n / 2 == 0 ->
let x = n * n * n
in
x - 1
| n ->
let x = n * n * n
in
x - 1
}
[-1..100]
List.map {
0 -> 0,
n if n / 2 == 0 ->
let x = n * n * n
in
x - 1,
n ->
let x = n * n * n
in
x - 1
}
[-1..100]
-- 1
List.map {
| 0 -> 0
| n if n / 2 == 0 -> n
| n -> n * n
}
[-1..100]
-- 2
List.map
do 0 -> 0
| n if n / 2 == 0 -> n
| n -> n * n
end
[-1..100]
-- 3
List.map
(fn 0 -> 0
| n if n / 2 == 0 -> n
| n -> n * n)
[-1..100]
List.map
(λ 0 -> 0
| n if n / 2 == 0 -> n
| n -> n * n)
[-1..100]
List.map
(\ 0 -> 0
| n -> n * n)
[-1..100]
-- Lambdas can use pattern matching with the `|` alternative operator.
-- The following lambda will replace 5 by 0.
map (do 5 -> 0 | x -> x * x end) [1..10]
[1..10 |> map match \x
| 5 -> 0
| x -> x * x
end
[1..10 |> map match \x
| 5 -> 0
| x -> x * x
end
[1..10 |> map do | 5 -> 0
| x -> x * x
[1..10 |> map fun | 5 -> 0
| x -> x * x
end
[1..10 |> map fun
| 5 -> 0
| x -> x * x
end
[1..10 |> map do
| 5 -> 0
| x -> x * x
end
let read_until file =
File.fold_while
(function
| Left r a -> Continue [a & r]
| Right r -> List.rev r)
[]
file
let read_until file =
File.fold_while
(fun Left r a -> Continue [a & r]
| Right r -> List.rev r)
[]
file
def read_until file =
File.fold_while
(fn Left r a -> Continue (a & r)
| Right r -> List.rev r)
[]
file
let read_until file =
File.fold_while file [] {
| Left r a -> Continue [a & r]
| Right r -> List.rev r
}
def read_until file =
File.fold_while {
Left r a =>
Continue [a & r]
Right r | List.rev r
}
[]
file
def read_until file =
File.fold_while
fun Left r a -> Continue [a & r]
| Right r -> List.rev r
end
[]
file
def read_until file =
file
|> File.fold_while {
| Left r a -> Continue [a & r]
| Right r -> List.rev r
}
[]
-- Length --
-- 1.0) SML style inline patterns
def length [_ & rest] = 1 + length rest
| length [] = 0
-- 2.0) Explicit match, ocaml style
def length list =
match list with
| [_ & rest] -> 1 + length rest
| [] -> 0
end
-- 2.1) Explicit match, ocaml style
def length list =
match list {
| [_ & rest] ->
1 + length rest
| [] ->
0
}
-- 3.0 Explicit match, rust style
def length list =
match list {
[_ & rest] -> 1 + length rest
[] -> 0
}
-- 3.1 Explicit match, rust style
def length list =
match list {
[_ & rest] ->
1 + length rest
[] ->
0
}
-- The same variable can be referenced multiple times.
\x + \x
-- * --
-> \ x y => x + y
-> \ 5
-> (~ + ~)
(-> system :fetcher :conf :credentials :username)
-> system #fetcher #conf #credentials #username
map (fn x flag -> process x verbose: (not flag)) [1, 2, 3, 4, 5]
map { process \x verbose: (not \flag) } [1, 2, 3, 4, 5]
map (data flag -> process data verbose: (not flag)) [1, 2, 3, 4, 5]
map (process _ verbose: (not _)) [1, 2, 3, 4, 5]
map { data flag -> process data verbose: (not flag) } [1, 2, 3, 4, 5]
map { process _ verbose: (not _) } [1, 2, 3, 4, 5]
map (data flag -> process data verbose: (not flag)) [1, 2, 3, 4, 5]
map {process _ verbose: (not _)} [1, 2, 3, 4, 5]
map (λ data flag -> process data verbose: (not flag)) [1, 2, 3, 4, 5]
map λ(process _ verbose: (not _)) [1, 2, 3, 4, 5]
map (data flag -> process data verbose: (not flag)) [1, 2, 3, 4, 5]
map {process _ verbose: (not _)} [1, 2, 3, 4, 5]
map (|data flag| -> process data verbose: (not flag)) [1, 2, 3, 4, 5]
map {process _ verbose: (not _)} [1, 2, 3, 4, 5]
-> map (|x| -> x * x) [1 .. 5]
= [1, 4, 9, 16, 25]
-> map \(_1 * _1) [1 .. 5]
= [1, 4, 9, 16, 25]
-> map \(_1 * _1) [1 .. 5]
= [1, 4, 9, 16, 25] : [Int]
-- Consider using _0 as a reference to the anonymous function, allowing this way recursion.
-- Mathematica
-- If[#1 == 1, 1, #1 * #0[#1-1]]&
-> \(_1 == 1 ? 1 : _1 * (_0 (_1 - 1)))
-> \(if (_1 == 1): 1 else: _1 * (_0 (_1 - 1)))
-> \(\1 == 1 ? 1 : @1 * (@0 (@1 - 1)))
fix = \f -> (\x a -> f (x x) a) (\x a -> f (x x) a)
fix = f -> (x a -> f (x x) a)
(x a -> f (x x) a)
-- // --
-- Anonymous functions can be wrapped in blocks.
[1..99] -> fold init: {} do dict i ->
dict # i::String <- i + i
end
[1..99]
|> fold (fn acc i -> acc!i <- i + i) (dict [])
-- This approach has some advantages over a simple lambda expression:
--
-- * Since blocks are used, at any time you can extend the block with new statements.
-- * `do` is a named argument for the lambda argument for `fold`.
squares = [1..9] -> map do n ->
n * n
end
squares = [1..9] >- map do n ->
n * n
end
squares = [1..9] -> map do n ->
n * n
end
squares = [1..9] -> map do n ->
n * n
end
for i <- [1..9]
print "hey there number {i}"
end
[print "hey there number {i}" | i <- [1..9]]
-- Lambda symbols
x y -> x + y
|x y| -> x + y
\x y -> x + y
fn x y -> x + y
do
x y -> x + y
end
fun x y -> x + y
lambda x y -> x + y
{ x y -> x + y }
{ x y -> x + y }
-- Patterns
def n + n =
Int.add n n
def (+) n n =
Int.add n n
def (+) = fn n -> fn n -> Int.add n n
(= (+ n n )
(Int.add n n))
pattern = expression
-- not a pattern
f x y = ?