Deprecate constant, compose

Author: lpil

Diff for: CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## Unreleased
+
+- The `compose` and `constant` functions in the `function` module have been
+  deprecated in favour of the `fn` literal syntax.
+
 ## v0.35.1 - 2024-02-15
 
 - Fixed a warning on the JavaScript target.

Diff for: src/gleam/function.gleam

@@ -1,6 +1,4 @@
-/// Takes two functions and chains them together to form one function that
-/// takes the input from the first and returns the output of the second.
-///
+@deprecated("Use a fn literal instead, it is easier to understand")
 pub fn compose(fun1: fn(a) -> b, fun2: fn(b) -> c) -> fn(a) -> c {
   fn(a) { fun2(fun1(a)) }
 }
@@ -103,9 +101,7 @@ pub fn identity(x: a) -> a {
   x
 }
 
-/// Takes a single argument and returns a new function that
-/// ignores its argument and always returns the input value.
-///
+@deprecated("Use a fn literal instead, it is easier to understand")
 pub fn constant(value: a) -> fn(b) -> a {
   fn(_) { value }
 }

Diff for: test/gleam/function_test.gleam

@@ -1,37 +1,9 @@
 import gleam/function
 import gleam/int
-import gleam/list
 import gleam/pair
-import gleam/result
 import gleam/should
 import gleam/string
 
-pub fn compose_test() {
-  let add_two = fn(int: Int) { int + 2 }
-  let add_three = fn(int: Int) { int + 3 }
-
-  let add_five = function.compose(add_two, add_three)
-
-  1
-  |> add_five
-  |> should.equal(6)
-
-  // Takes a list of ints and returns the first as a string (if there is one, or
-  // else "0" if there is not)
-  let first_to_string =
-    list.first
-    |> function.compose(result.unwrap(_, 0))
-    |> function.compose(int.to_string)
-
-  [1]
-  |> first_to_string
-  |> should.equal("1")
-
-  []
-  |> first_to_string
-  |> should.equal("0")
-}
-
 pub fn curry2_test() {
   let fun = fn(a, b) { a + b }
   let curried = function.curry2(fun)
@@ -108,12 +80,6 @@ pub fn identity_test() {
   |> should.equal(#(1, 2.0))
 }
 
-pub fn constant_test() {
-  #(1, 2)
-  |> pair.map_first(function.constant(42))
-  |> should.equal(#(42, 2))
-}
-
 pub fn tap_test() {
   "Thanks Joe & Louis"
   |> function.tap(fn(s: String) {