From 43eaa6bf4e94561d2a53dc69df17bf80d43a0ed5 Mon Sep 17 00:00:00 2001
From: Kristof Bastiaensen 3e <kba@3e.eu>
Date: Fri, 4 Jun 2021 14:42:05 +0200
Subject: [PATCH] improve error messages for `lookup`

---
 CHANGES.md                 | 4 ++++
 cassava.cabal              | 2 +-
 src/Data/Csv/Conversion.hs | 5 ++++-
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/CHANGES.md b/CHANGES.md
index e97cf00..fbd3f76 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,7 @@
+## Version 0.5.3.0
+
+ * improve error messages for `lookup` and NamedRecord parsers.
+
 ## Version 0.5.2.0
 
  * Add `FromField`/`ToField` instances for `Identity` and `Const` (#158)
diff --git a/cassava.cabal b/cassava.cabal
index 5607650..775e448 100644
--- a/cassava.cabal
+++ b/cassava.cabal
@@ -1,6 +1,6 @@
 cabal-version:       1.12
 Name:                cassava
-Version:             0.5.2.0
+Version:             0.5.3.0
 Synopsis:            A CSV parsing and encoding library
 Description: {
 
diff --git a/src/Data/Csv/Conversion.hs b/src/Data/Csv/Conversion.hs
index 1f2ab84..574e9e2 100644
--- a/src/Data/Csv/Conversion.hs
+++ b/src/Data/Csv/Conversion.hs
@@ -1148,8 +1148,11 @@ unsafeIndex v idx = parseField (V.unsafeIndex v idx)
 -- 'empty' if the field is missing or if the value cannot be converted
 -- to the desired type.
 lookup :: FromField a => NamedRecord -> B.ByteString -> Parser a
-lookup m name = maybe (fail err) parseField $ HM.lookup name m
+lookup m name = maybe (fail err) parseField' $ HM.lookup name m
   where err = "no field named " ++ show (B8.unpack name)
+        parseField' fld = case runParser (parseField fld) of
+          Left e -> fail $ "in named field " ++ show (B8.unpack name) ++ ": " ++ e
+          Right res -> pure res
 {-# INLINE lookup #-}
 
 -- | Alias for 'lookup'.