From 7ef601e5f01d3f63d93a88675754bd745267d71a Mon Sep 17 00:00:00 2001
From: Louis Pilfold <louis@lpil.uk>
Date: Tue, 17 Sep 2019 20:52:37 +0100
Subject: Unify error types

---
 src/gleam/int.gleam   |  5 +----
 src/gleam/list.gleam  | 19 ++++++-------------
 src/gleam/map.gleam   |  9 ++-------
 src/gleam__stdlib.erl |  4 ++--
 4 files changed, 11 insertions(+), 26 deletions(-)

(limited to 'src')

diff --git a/src/gleam/int.gleam b/src/gleam/int.gleam
index 2fed6bd..7a83fba 100644
--- a/src/gleam/int.gleam
+++ b/src/gleam/int.gleam
@@ -1,9 +1,6 @@
 import gleam/order
 
-pub enum NotAnInt =
-  | NotAnInt
-
-pub external fn parse(String) -> Result(Int, NotAnInt) = "gleam__stdlib" "parse_int";
+pub external fn parse(String) -> Result(Int, Nil) = "gleam__stdlib" "parse_int";
 
 pub external fn to_string(Int) -> String = "erlang" "integer_to_binary"
 
diff --git a/src/gleam/list.gleam b/src/gleam/list.gleam
index ed63a4b..2df547c 100644
--- a/src/gleam/list.gleam
+++ b/src/gleam/list.gleam
@@ -2,14 +2,7 @@ import gleam/int
 import gleam/order
 import gleam/pair
 
-pub enum Empty =
-  | Empty
-
-pub enum NotFound =
-  | NotFound
-
-pub enum LengthMismatch =
-  | LengthMismatch
+pub struct LengthMismatch {}
 
 // Using the Erlang C BIF implementation.
 //
@@ -32,14 +25,14 @@ pub fn contains(list, elem) {
 
 pub fn head(list) {
   case list {
-  | [] -> Error(Empty)
+  | [] -> Error(Nil)
   | [x | _] -> Ok(x)
   }
 }
 
 pub fn tail(list) {
   case list {
-  | [] -> Error(Empty)
+  | [] -> Error(Nil)
   | [_ | xs] -> Ok(xs)
   }
 }
@@ -157,7 +150,7 @@ pub fn fold_right(list, acc, fun) {
 
 pub fn find(haystack, f) {
   case haystack {
-  | [] -> Error(NotFound)
+  | [] -> Error(Nil)
   | [x | rest] ->
       case f(x) {
       | Ok(x) -> Ok(x)
@@ -213,10 +206,10 @@ pub fn intersperse(list, elem) {
 
 pub fn at(list, i) {
   case i < 0 {
-    | True -> Error(NotFound)
+    | True -> Error(Nil)
     | False ->
       case list {
-        | [] -> Error(NotFound)
+        | [] -> Error(Nil)
         | [x | rest] ->
           case i == 0 {
           | True -> Ok(x)
diff --git a/src/gleam/map.gleam b/src/gleam/map.gleam
index 935f3cb..b46590d 100644
--- a/src/gleam/map.gleam
+++ b/src/gleam/map.gleam
@@ -5,9 +5,6 @@ import gleam/pair
 
 pub external type MapDict(key, value);
 
-pub enum NotFound =
-  | NotFound
-
 pub external fn size(MapDict(k, v)) -> Int
   = "maps" "size"
 
@@ -27,7 +24,7 @@ pub fn has_key(map, key) {
 pub external fn new() -> MapDict(key, value)
   = "maps" "new"
 
-pub external fn fetch(MapDict(key, value), key) -> Result(value, NotFound)
+pub external fn fetch(MapDict(key, value), key) -> Result(value, Nil)
   = "gleam__stdlib" "map_fetch";
 
 external fn erl_put(key, value, MapDict(key, value)) -> MapDict(key, value)
@@ -79,12 +76,10 @@ pub fn drop(map, keys) {
   })
 }
 
-pub external type NotFound;
-
 pub fn update(dict, key, f) {
   case fetch(dict, key) {
   | Ok(value) -> put(dict, key, f(Ok(value)))
-  | Error(_) -> put(dict, key, f(Error(NotFound)))
+  | Error(_) -> put(dict, key, f(Error(Nil)))
   }
 }
 
diff --git a/src/gleam__stdlib.erl b/src/gleam__stdlib.erl
index 55e847d..b9236ed 100644
--- a/src/gleam__stdlib.erl
+++ b/src/gleam__stdlib.erl
@@ -17,7 +17,7 @@ expect_is_error(A) -> ?assertMatch({error, _}, A).
 
 map_fetch(Map, Key) ->
   case maps:find(Key, Map) of
-    error -> {error, not_found};
+    error -> {error, nil};
     OkFound -> OkFound
   end.
 
@@ -79,7 +79,7 @@ parse_int(String) ->
       {ok, Integer};
 
     _ ->
-      {error, parse_error}
+      {error, nil}
   end.
 
 parse_float(String) ->
-- 
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