From 3fb91e0f448aa4be317a112fdc95673fb99fa6f6 Mon Sep 17 00:00:00 2001
From: aarne <unknown>
Date: Tue, 15 Jun 2004 13:55:54 +0000
Subject: improved make facility: remember state if fails; does not need source

---
 src/GF/Data/Operations.hs | 9 +++++++++
 1 file changed, 9 insertions(+)

(limited to 'src/GF/Data')

diff --git a/src/GF/Data/Operations.hs b/src/GF/Data/Operations.hs
index 9c374fe83..9bed80392 100644
--- a/src/GF/Data/Operations.hs
+++ b/src/GF/Data/Operations.hs
@@ -122,6 +122,15 @@ mapErrN maxN f xs = Ok (ys, unlines (errHdr : ss2))
     nss = length ss
     fxs = map f xs
 
+-- like foldM, but also return the latest value if fails
+
+foldErr :: (a -> b -> Err a) -> a -> [b] -> Err (a, Maybe String)
+foldErr f s xs = case xs of
+  [] -> return (s,Nothing)
+  x:xx -> case f s x of
+    Ok v  -> foldErr f v xx
+    Bad m -> return $ (s, Just m)
+
 -- !! with the error monad
 (!?) :: [a] -> Int -> Err a
 xs !? i = foldr (const . return) (Bad "too few elements in list") $ drop i xs
-- 
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