From: ross <unknown>
Date: Fri, 21 Oct 2005 10:24:58 +0000 (+0000)
Subject: [project @ 2005-10-21 10:24:58 by ross]
X-Git-Tag: cmm-merge2~3
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;ds=sidebyside;h=b0f8af46ab1a89f107f2d678d17b765cd97ff59f;p=haskell-directory.git

[project @ 2005-10-21 10:24:58 by ross]
export parens, which is useful for writing Read instances.
---

diff --git a/Text/Read.hs b/Text/Read.hs
index 16a4d15..bcb2d09 100644
--- a/Text/Read.hs
+++ b/Text/Read.hs
@@ -35,6 +35,7 @@ module Text.Read (
    module Text.ParserCombinators.ReadPrec,
    L.Lexeme(..),	
    lexP,		-- :: ReadPrec Lexeme
+   parens,		-- :: ReadPrec a -> ReadPrec a
 #endif
 #ifdef __GLASGOW_HASKELL__
    readListDefault,	-- :: Read a => ReadS [a]
@@ -56,4 +57,14 @@ import qualified Text.Read.Lex as L
 
 lexP :: ReadPrec L.Lexeme
 lexP = lift L.lex
+
+parens :: ReadPrec a -> ReadPrec a
+parens p = optional
+ where
+  optional  = p +++ mandatory
+  mandatory = do
+    L.Punc "(" <- lexP
+    x          <- reset optional
+    L.Punc ")" <- lexP
+    return x
 #endif