Add generic module

Containing identity, always, flip, and compose functions.

1 files changed, 66 insertions, 0 deletions

diff --git a/test/gleam/generic_test.gleam b/test/gleam/generic_test.gleam
new file mode 100644
index 0000000..a65e931
--- /dev/null
+++ b/test/gleam/generic_test.gleam
@@ -0,0 +1,66 @@
+import gleam/expect
+import gleam/generic.{identity, always, flip, compose}
+import gleam/int as int_mod
+import gleam/list
+import gleam/result
+import gleam/string as string_mod
+
+pub fn identity_test() {
+  1
+  |> identity
+  |> expect.equal(_, 1)
+}
+
+pub fn always_test() {
+  1
+  |> always(_, 2)
+  |> expect.equal(_, 2)
+}
+
+pub fn flip_test() {
+  let fun = fn(string: String, int: Int) {
+    string
+    |> string_mod.append("String: '", _)
+    |> string_mod.append(_, "', Int: '")
+    |> string_mod.append(_, int_mod.to_string(int))
+    |> string_mod.append(_, "'")
+  }
+
+  let flipped_fun = flip(fun)
+
+  fun("Bob", 1)
+  |> expect.equal(_, "String: 'Bob', Int: '1'")
+
+  flipped_fun(2, "Alice")
+  |> expect.equal(_, "String: 'Alice', Int: '2'")
+}
+
+pub fn compose_test() {
+  let add_two = fn(int: Int) { int + 2 }
+  let add_three = fn(int: Int) { int + 3 }
+
+  let add_five = compose(add_two, add_three)
+
+  1
+  |> add_five
+  |> expect.equal(_, 6)
+
+  // Takes a list of ints and returns the head as a string (if there is one, or
+  // else "0" if there is not)
+  let head_to_string =
+    compose(
+      list.head,
+      fn(int_result: Result(Int, Nil)) {
+        result.unwrap(int_result, 0)
+        |> int_mod.to_string
+      }
+    )
+
+  [1]
+  |> head_to_string
+  |> expect.equal(_, "1")
+
+  []
+  |> head_to_string
+  |> expect.equal(_, "0")
+}