Add `float:compare` function to stdlib

Fixes #209

4 files changed, 58 insertions, 2 deletions

diff --git a/gen/src/gleam@float.erl b/gen/src/gleam@float.erl
index 0d8ec08..1d19fc7 100644
--- a/gen/src/gleam@float.erl
+++ b/gen/src/gleam@float.erl
@@ -1,7 +1,7 @@
 -module(gleam@float).
 -compile(no_auto_import).
 
--export([parse/1, to_string/1, ceiling/1, floor/1, round/1, truncate/1]).
+-export([parse/1, to_string/1, compare/2, ceiling/1, floor/1, round/1, truncate/1]).
 
 parse(A) ->
     gleam__stdlib:parse_float(A).
@@ -9,6 +9,21 @@ parse(A) ->
 to_string(F) ->
     gleam@iodata:to_string(gleam@iodata:from_float(F)).
 
+compare(A, B) ->
+    case A =:= B of
+        true ->
+            eq;
+
+        false ->
+            case A < B of
+                true ->
+                    lt;
+
+                false ->
+                    gt
+            end
+    end.
+
 ceiling(A) ->
     math:ceil(A).
 
diff --git a/gen/test/gleam@float_test.erl b/gen/test/gleam@float_test.erl
index ea19c5e..403be9d 100644
--- a/gen/test/gleam@float_test.erl
+++ b/gen/test/gleam@float_test.erl
@@ -1,7 +1,7 @@
 -module(gleam@float_test).
 -compile(no_auto_import).
 
--export([parse_test/0, to_string_test/0, ceiling_test/0, floor_test/0, round_test/0, truncate_test/0]).
+-export([parse_test/0, to_string_test/0, compare_test/0, ceiling_test/0, floor_test/0, round_test/0, truncate_test/0]).
 
 parse_test() ->
     gleam@expect:equal(gleam@float:parse(<<"1.23">>), {ok, 1.23}),
@@ -15,6 +15,14 @@ to_string_test() ->
     gleam@expect:equal(gleam@float:to_string(123.0), <<"123.0">>),
     gleam@expect:equal(gleam@float:to_string(-8.1), <<"-8.1">>).
 
+compare_test() ->
+    gleam@expect:equal(gleam@float:compare(0.0, 0.0), eq),
+    gleam@expect:equal(gleam@float:compare(0.1, 0.1), eq),
+    gleam@expect:equal(gleam@float:compare(0.0, 0.1), lt),
+    gleam@expect:equal(gleam@float:compare(-2.0, -1.9), lt),
+    gleam@expect:equal(gleam@float:compare(2.0, 1.9), gt),
+    gleam@expect:equal(gleam@float:compare(-1.9, -2.0), gt).
+
 ceiling_test() ->
     gleam@expect:equal(gleam@float:ceiling(8.1), 9.0),
     gleam@expect:equal(gleam@float:ceiling(-8.1), -8.0),
diff --git a/src/gleam/float.gleam b/src/gleam/float.gleam
index b1ae86e..65be088 100644
--- a/src/gleam/float.gleam
+++ b/src/gleam/float.gleam
@@ -1,4 +1,5 @@
 import gleam/iodata
+import gleam/order
 
 pub enum NotAFloat =
   | NotAFloat
@@ -12,6 +13,17 @@ pub fn to_string(f) {
   |> iodata:to_string
 }
 
+pub fn compare(a, b) {
+  case a == b {
+  | True -> order:Eq
+  | False ->
+    case a <. b {
+    | True -> order:Lt
+    | False -> order:Gt
+    }
+  }
+}
+
 pub external fn ceiling(Float) -> Float = "math" "ceil";
 
 pub external fn floor(Float) -> Float = "math" "floor";
diff --git a/test/gleam/float_test.gleam b/test/gleam/float_test.gleam
index 41b5ed1..ef063a5 100644
--- a/test/gleam/float_test.gleam
+++ b/test/gleam/float_test.gleam
@@ -1,5 +1,6 @@
 import gleam/expect
 import gleam/float
+import gleam/order
 
 pub fn parse_test() {
   "1.23"
@@ -37,6 +38,26 @@ pub fn to_string_test() {
   |> expect:equal(_, "-8.1")
 }
 
+pub fn compare_test() {
+  float:compare(0., 0.)
+  |> expect:equal(_, order:Eq)
+
+  float:compare(0.1, 0.1)
+  |> expect:equal(_, order:Eq)
+
+  float:compare(0., 0.1)
+  |> expect:equal(_, order:Lt)
+
+  float:compare(-2., -1.9)
+  |> expect:equal(_, order:Lt)
+
+  float:compare(2., 1.9)
+  |> expect:equal(_, order:Gt)
+
+  float:compare(-1.9, -2.)
+  |> expect:equal(_, order:Gt)
+}
+
 pub fn ceiling_test() {
   8.1
   |> float:ceiling