From 6a701d1b1943891ee866e22c5d84800ade8c09f1 Mon Sep 17 00:00:00 2001
From: Louis Pilfold <louis@lpil.uk>
Date: Thu, 22 Feb 2024 14:08:30 +0000
Subject: [PATCH] Deprecate constant, compose

---
 CHANGELOG.md                   |  5 +++++
 src/gleam/function.gleam       |  8 ++------
 test/gleam/function_test.gleam | 34 ----------------------------------
 3 files changed, 7 insertions(+), 40 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 846dc7ed..af7ed730 100644
--- a/CHANGELOG.md
+++ b/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 --git a/src/gleam/function.gleam b/src/gleam/function.gleam
index 180b6b21..6f424557 100644
--- a/src/gleam/function.gleam
+++ b/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 --git a/test/gleam/function_test.gleam b/test/gleam/function_test.gleam
index 26919f26..ce3c08fa 100644
--- a/test/gleam/function_test.gleam
+++ b/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) {