From 52b3b5f889dfecfd4c1a1a2dfd570fbbdc2ac0c2 Mon Sep 17 00:00:00 2001
From: osmarks <osmarks@protonmail.com>
Date: Thu, 17 Aug 2017 15:30:43 +0100
Subject: [PATCH] Give parse more useful output, add more useful errors

---
 src/Expr.elm | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/Expr.elm b/src/Expr.elm
index 3cd7952..f9f9f9d 100644
--- a/src/Expr.elm
+++ b/src/Expr.elm
@@ -16,7 +16,8 @@ type Expr
 
 num : Parser () Expr
 num =
-    Num <$> Num.float <|> Num << toFloat <$> Num.int
+    (Num <$> Num.float <|> Num << toFloat <$> Num.int)
+    <?> "expected a number (int or float)"
 
 stringIs : String -> a -> Parser s a
 stringIs str val =
@@ -33,12 +34,15 @@ op =
 group : Parser () Expr
 group =
     between (string "(") (string ")") (sepBy1 whitespace (lazy <| \_ -> parser)) -- Avoid bad recursion issues using lazy parser evaluation
+    <?> "expected a group (whitespace-separated expressions between brackets)"
     |> map Group
 
 parser : Parser () Expr
 parser =
     (lazy <| \_ -> group) <|> op <|> num
 
-parse : String -> Result (ParseErr ()) (ParseOk () Expr)
+parse : String -> Result (List String) Expr
 parse =
-    Combine.parse parser
\ No newline at end of file
+    Combine.parse parser
+    >> Result.mapError (\(_, _, errorList) -> errorList)
+    >> Result.map (\(_, _, expr) -> expr) -- Convert errors/results to nicer format
\ No newline at end of file