From 5bb792be5e3416a2229d549d57f02b54829c470b Mon Sep 17 00:00:00 2001
From: hallgren <hallgren@chalmers.se>
Date: Tue, 1 Dec 2015 15:14:27 +0000
Subject: [PATCH] GF.Data.Str: change matchPrefix to agree with the GF book and
 the run-time system

The matchPrefix function is used in str2strings and the partial evaluator to
compute pre{...} tokens. But unlike the description in the GF book and
the implementation in the run-time system, matchPrefix looked at
the concatenation(!) of all following tokens and not just the next token
when deciding how to compute a pre{...} token.

This is a backwards incompatible change, but it is subtle and probably won't
cause any problems. In particular, the example grammars are unaffected.
---
 src/compiler/GF/Data/Str.hs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/GF/Data/Str.hs b/src/compiler/GF/Data/Str.hs
index 7b79add0a..7f1f4db75 100644
--- a/src/compiler/GF/Data/Str.hs
+++ b/src/compiler/GF/Data/Str.hs
@@ -44,8 +44,8 @@ type Ss = [String]
 -- matching functions in both ways
 
 matchPrefix :: Ss -> [(Ss,[String])] -> [String] -> Ss
-matchPrefix s vs t = 
-  head $ [u | let t' = concat (unmarkup t),
+matchPrefix s vs t =
+  head $ [u | t':_ <- [unmarkup t],
               (u,as) <- vs,
               any (`isPrefixOf` t') as]
          ++ [s]