X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Futils%2FUtil.lhs;h=ed7ee9aca6a27aadcc5d4c32a241b65d3e795506;hb=423d477bfecd490de1449c59325c8776f91d7aac;hp=5b4200b4db27d8328d0c7989a6c4b32541df6f0e;hpb=904f158f9fe208b8154029dff655a6eab4b2828e;p=ghc-hetmet.git

diff --git a/ghc/compiler/utils/Util.lhs b/ghc/compiler/utils/Util.lhs
index 5b4200b..ed7ee9a 100644
--- a/ghc/compiler/utils/Util.lhs
+++ b/ghc/compiler/utils/Util.lhs
@@ -1,60 +1,78 @@
 %
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
+% (c) The University of Glasgow 1992-2002
 %
 \section[Util]{Highly random utility functions}
 
 \begin{code}
--- IF_NOT_GHC is meant to make this module useful outside the context of GHC
-#define IF_NOT_GHC(a)
-
 module Util (
-	-- The Eager monad
-	Eager, thenEager, returnEager, mapEager, appEager, runEager,
 
 	-- general list processing
 	zipEqual, zipWithEqual, zipWith3Equal, zipWith4Equal,
-        zipLazy, stretchZipEqual,
+        zipLazy, stretchZipWith,
 	mapAndUnzip, mapAndUnzip3,
-	nOfThem, lengthExceeds, isSingleton, only,
-	snocView,
-	isIn, isn'tIn,
+	nOfThem, filterOut,
+	lengthExceeds, lengthIs, lengthAtLeast, listLengthCmp, atLength,
+	isSingleton, only,
+	notNull, snocView,
 
-	-- association lists
-	assoc, assocUsing, assocDefault, assocDefaultUsing,
+	isIn, isn'tIn,
 
-	-- duplicate handling
-	hasNoDups, equivClasses, runs, removeDups, equivClassesByUniq,
+	-- for-loop
+	nTimes,
 
 	-- sorting
-	IF_NOT_GHC(quicksort COMMA stableSortLt COMMA mergesort COMMA)
-	sortLt,
-	IF_NOT_GHC(mergeSort COMMA) naturalMergeSortLe,	-- from Carsten
-	IF_NOT_GHC(naturalMergeSort COMMA mergeSortLe COMMA)
+	sortLt, naturalMergeSortLe,
 
 	-- transitive closures
 	transitiveClosure,
 
 	-- accumulating
-	mapAccumL, mapAccumR, mapAccumB, foldl2, count,
+	mapAccumL, mapAccumR, mapAccumB, 
+	foldl2, count,
+	
+	takeList, dropList, splitAtList,
 
 	-- comparisons
-	thenCmp, cmpList,
+	eqListBy, equalLength, compareLength,
+	thenCmp, cmpList, prefixMatch, suffixMatch, maybePrefixMatch,
 
 	-- strictness
-	seqList, ($!),
+	foldl', seqList,
 
 	-- pairs
-	IF_NOT_GHC(cfst COMMA applyToPair COMMA applyToFst COMMA)
-	IF_NOT_GHC(applyToSnd COMMA foldPair COMMA)
-	unzipWith
+	unzipWith,
+
+	global,
+
+	-- module names
+	looksLikeModuleName,
+	
+	toArgs,
+
+	-- Floating point stuff
+	readRational,
     ) where
 
+#include "../includes/ghcconfig.h"
 #include "HsVersions.h"
 
+import Panic		( panic, trace )
+import FastTypes
+
+#if __GLASGOW_HASKELL__ <= 408
+import EXCEPTION	( catchIO, justIoErrors, raiseInThread )
+#endif
+import DATA_IOREF	( IORef, newIORef )
+import UNSAFE_IO	( unsafePerformIO )
+
+import qualified List	( elem, notElem )
+
+#ifndef DEBUG
 import List		( zipWith4 )
-import Panic		( panic )
-import Unique		( Unique )
-import UniqFM		( eltsUFM, emptyUFM, addToUFM_C )
+#endif
+
+import Char		( isUpper, isAlphaNum, isSpace, ord, isDigit )
+import Ratio		( (%) )
 
 infixr 9 `thenCmp`
 \end{code}
@@ -70,6 +88,8 @@ used to allow you to express "do this and then that", mainly to avoid
 space leaks. It's done with a type synonym to save bureaucracy.
 
 \begin{code}
+#if NOT_USED
+
 type Eager ans a = (a -> ans) -> ans
 
 runEager :: Eager a a -> a
@@ -89,6 +109,21 @@ mapEager f [] = returnEager []
 mapEager f (x:xs) = f x			`thenEager` \ y ->
 		    mapEager f xs	`thenEager` \ ys ->
 		    returnEager (y:ys)
+#endif
+\end{code}
+
+%************************************************************************
+%*									*
+\subsection{A for loop}
+%*									*
+%************************************************************************
+
+\begin{code}
+-- Compose a function with itself n times.  (nth rather than twice)
+nTimes :: Int -> (a -> a) -> (a -> a)
+nTimes 0 _ = id
+nTimes 1 f = f
+nTimes n f = f . nTimes (n-1) f
 \end{code}
 
 %************************************************************************
@@ -97,6 +132,14 @@ mapEager f (x:xs) = f x			`thenEager` \ y ->
 %*									*
 %************************************************************************
 
+\begin{code}
+filterOut :: (a->Bool) -> [a] -> [a]
+-- Like filter, only reverses the sense of the test
+filterOut p [] = []
+filterOut p (x:xs) | p x       = filterOut p xs
+		   | otherwise = x : filterOut p xs
+\end{code}
+
 A paranoid @zip@ (and some @zipWith@ friends) that checks the lists
 are of equal length.  Alastair Reid thinks this should only happen if
 DEBUGging on; hey, why not?
@@ -143,13 +186,16 @@ zipLazy (x:xs) ~(y:ys) = (x,y) : zipLazy xs ys
 
 
 \begin{code}
-stretchZipEqual :: (a -> b -> Maybe a) -> [a] -> [b] -> [a]
--- (stretchZipEqual f xs ys) stretches ys to "fit" the places where f returns a Just
+stretchZipWith :: (a -> Bool) -> b -> (a->b->c) -> [a] -> [b] -> [c]
+-- (stretchZipWith p z f xs ys) stretches ys by inserting z in 
+-- the places where p returns *True*
 
-stretchZipEqual f [] [] = []
-stretchZipEqual f (x:xs) (y:ys) = case f x y of
-				    Just x' -> x' : stretchZipEqual f xs ys
-				    Nothing -> x  : stretchZipEqual f xs (y:ys)
+stretchZipWith p z f [] ys = []
+stretchZipWith p z f (x:xs) ys
+  | p x       = f x z : stretchZipWith p z f xs ys
+  | otherwise = case ys of
+		  []     -> []
+		  (y:ys) -> f x y : stretchZipWith p z f xs ys
 \end{code}
 
 
@@ -179,15 +225,66 @@ mapAndUnzip3 f (x:xs)
 nOfThem :: Int -> a -> [a]
 nOfThem n thing = replicate n thing
 
+-- 'atLength atLen atEnd ls n' unravels list 'ls' to position 'n';
+-- specification:
+--
+--  atLength atLenPred atEndPred ls n
+--   | n < 0         = atLenPred n
+--   | length ls < n = atEndPred (n - length ls)
+--   | otherwise     = atLenPred (drop n ls)
+--
+atLength :: ([a] -> b)
+         -> (Int -> b)
+         -> [a]
+         -> Int
+         -> b
+atLength atLenPred atEndPred ls n 
+  | n < 0     = atEndPred n 
+  | otherwise = go n ls
+  where
+    go n [] = atEndPred n
+    go 0 ls = atLenPred ls
+    go n (_:xs) = go (n-1) xs
+
+-- special cases.
 lengthExceeds :: [a] -> Int -> Bool
--- (lengthExceeds xs n) is True if   length xs > n
-(x:xs)	`lengthExceeds` n = n < 1 || xs `lengthExceeds` (n - 1)
-[]	`lengthExceeds` n = n < 0
+-- (lengthExceeds xs n) = (length xs > n)
+lengthExceeds = atLength notNull (const False)
+
+lengthAtLeast :: [a] -> Int -> Bool
+lengthAtLeast = atLength notNull (== 0)
+
+lengthIs :: [a] -> Int -> Bool
+lengthIs = atLength null (==0)
+
+listLengthCmp :: [a] -> Int -> Ordering 
+listLengthCmp = atLength atLen atEnd 
+ where
+  atEnd 0      = EQ
+  atEnd x
+   | x > 0     = LT -- not yet seen 'n' elts, so list length is < n.
+   | otherwise = GT
+
+  atLen []     = EQ
+  atLen _      = GT
 
 isSingleton :: [a] -> Bool
 isSingleton [x] = True
 isSingleton  _  = False
 
+notNull :: [a] -> Bool
+notNull [] = False
+notNull _  = True
+
+snocView :: [a] -> Maybe ([a],a)
+	-- Split off the last element
+snocView [] = Nothing
+snocView xs = go [] xs
+	    where
+		-- Invariant: second arg is non-empty
+	      go acc [x]    = Just (reverse acc, x)
+	      go acc (x:xs) = go (x:acc) xs
+
 only :: [a] -> a
 #ifdef DEBUG
 only [a] = a
@@ -196,14 +293,6 @@ only (a:_) = a
 #endif
 \end{code}
 
-\begin{code}
-snocView :: [a] -> ([a], a)	-- Split off the last element
-snocView xs = go xs []
-	    where
-	      go [x]    acc = (reverse acc, x)
-	      go (x:xs) acc = go xs (x:acc)
-\end{code}
-
 Debugging/specialising versions of \tr{elem} and \tr{notElem}
 
 \begin{code}
@@ -220,134 +309,25 @@ elem__ x (y:ys)	= x==y || elem__ x ys
 notElem__ x []	   =  True
 notElem__ x (y:ys) =  x /= y && notElem__ x ys
 
-# else {- DEBUG -}
+# else /* DEBUG */
 isIn msg x ys
-  = elem ILIT(0) x ys
+  = elem (_ILIT 0) x ys
   where
     elem i _ []	    = False
     elem i x (y:ys)
-      | i _GE_ ILIT(100) = panic ("Over-long elem in: " ++ msg)
-      | otherwise	 = x == y || elem (i _ADD_ ILIT(1)) x ys
+      | i ># _ILIT 100 = trace ("Over-long elem in " ++ msg) $
+			 x `List.elem` (y:ys)
+      | otherwise      = x == y || elem (i +# _ILIT(1)) x ys
 
 isn'tIn msg x ys
-  = notElem ILIT(0) x ys
+  = notElem (_ILIT 0) x ys
   where
     notElem i x [] =  True
     notElem i x (y:ys)
-      | i _GE_ ILIT(100) = panic ("Over-long notElem in: " ++ msg)
-      | otherwise	 =  x /= y && notElem (i _ADD_ ILIT(1)) x ys
-
-# endif {- DEBUG -}
-
-\end{code}
-
-%************************************************************************
-%*									*
-\subsection[Utils-assoc]{Association lists}
-%*									*
-%************************************************************************
-
-See also @assocMaybe@ and @mkLookupFun@ in module @Maybes@.
-
-\begin{code}
-assoc		  :: (Eq a) => String -> [(a, b)] -> a -> b
-assocDefault	  :: (Eq a) => b -> [(a, b)] -> a -> b
-assocUsing	  :: (a -> a -> Bool) -> String -> [(a, b)] -> a -> b
-assocDefaultUsing :: (a -> a -> Bool) -> b -> [(a, b)] -> a -> b
-
-assocDefaultUsing eq deflt ((k,v) : rest) key
-  | k `eq` key = v
-  | otherwise  = assocDefaultUsing eq deflt rest key
-
-assocDefaultUsing eq deflt [] key = deflt
-
-assoc crash_msg         list key = assocDefaultUsing (==) (panic ("Failed in assoc: " ++ crash_msg)) list key
-assocDefault deflt      list key = assocDefaultUsing (==) deflt list key
-assocUsing eq crash_msg list key = assocDefaultUsing eq (panic ("Failed in assoc: " ++ crash_msg)) list key
-\end{code}
-
-%************************************************************************
-%*									*
-\subsection[Utils-dups]{Duplicate-handling}
-%*									*
-%************************************************************************
-
-\begin{code}
-hasNoDups :: (Eq a) => [a] -> Bool
-
-hasNoDups xs = f [] xs
-  where
-    f seen_so_far []     = True
-    f seen_so_far (x:xs) = if x `is_elem` seen_so_far then
-				False
-			   else
-				f (x:seen_so_far) xs
-
-    is_elem = isIn "hasNoDups"
-\end{code}
-
-\begin{code}
-equivClasses :: (a -> a -> Ordering) 	-- Comparison
-	     -> [a]
-	     -> [[a]]
-
-equivClasses cmp stuff@[]     = []
-equivClasses cmp stuff@[item] = [stuff]
-equivClasses cmp items
-  = runs eq (sortLt lt items)
-  where
-    eq a b = case cmp a b of { EQ -> True; _ -> False }
-    lt a b = case cmp a b of { LT -> True; _ -> False }
-\end{code}
-
-The first cases in @equivClasses@ above are just to cut to the point
-more quickly...
-
-@runs@ groups a list into a list of lists, each sublist being a run of
-identical elements of the input list. It is passed a predicate @p@ which
-tells when two elements are equal.
-
-\begin{code}
-runs :: (a -> a -> Bool) 	-- Equality
-     -> [a]
-     -> [[a]]
-
-runs p []     = []
-runs p (x:xs) = case (span (p x) xs) of
-		  (first, rest) -> (x:first) : (runs p rest)
-\end{code}
-
-\begin{code}
-removeDups :: (a -> a -> Ordering) 	-- Comparison function
-	   -> [a]
-	   -> ([a], 	-- List with no duplicates
-	       [[a]])	-- List of duplicate groups.  One representative from
-			-- each group appears in the first result
-
-removeDups cmp []  = ([], [])
-removeDups cmp [x] = ([x],[])
-removeDups cmp xs
-  = case (mapAccumR collect_dups [] (equivClasses cmp xs)) of { (dups, xs') ->
-    (xs', dups) }
-  where
-    collect_dups dups_so_far [x]         = (dups_so_far,      x)
-    collect_dups dups_so_far dups@(x:xs) = (dups:dups_so_far, x)
-\end{code}
-
-
-\begin{code}
-equivClassesByUniq :: (a -> Unique) -> [a] -> [[a]]
-	-- NB: it's *very* important that if we have the input list [a,b,c],
-	-- where a,b,c all have the same unique, then we get back the list
-	-- 	[a,b,c]
-	-- not
-	--	[c,b,a]
-	-- Hence the use of foldr, plus the reversed-args tack_on below
-equivClassesByUniq get_uniq xs
-  = eltsUFM (foldr add emptyUFM xs)
-  where
-    add a ufm = addToUFM_C tack_on ufm (get_uniq a) [a]
-    tack_on old new = new++old
+      | i ># _ILIT 100 = trace ("Over-long notElem in " ++ msg) $
+		         x `List.notElem` (y:ys)
+      | otherwise      =  x /= y && notElem (i +# _ILIT(1)) x ys
+# endif /* DEBUG */
 \end{code}
 
 %************************************************************************
@@ -363,6 +343,8 @@ equivClassesByUniq get_uniq xs
 %************************************************************************
 
 \begin{code}
+#if NOT_USED
+
 -- tail-recursive, etc., "quicker sort" [as per Meira thesis]
 quicksort :: (a -> a -> Bool)		-- Less-than predicate
 	  -> [a]			-- Input list
@@ -375,14 +357,13 @@ quicksort lt (x:xs)  = split x [] [] xs
     split x lo hi []		     = quicksort lt lo ++ (x : quicksort lt hi)
     split x lo hi (y:ys) | y `lt` x  = split x (y:lo) hi ys
 			 | True      = split x lo (y:hi) ys
+#endif
 \end{code}
 
 Quicksort variant from Lennart's Haskell-library contribution.  This
 is a {\em stable} sort.
 
 \begin{code}
-stableSortLt = sortLt	-- synonym; when we want to highlight stable-ness
-
 sortLt :: (a -> a -> Bool) 		-- Less-than predicate
        -> [a] 				-- Input list
        -> [a]				-- Result list
@@ -441,6 +422,7 @@ rqpart lt x (y:ys) rle rgt r =
 %************************************************************************
 
 \begin{code}
+#if NOT_USED
 mergesort :: (a -> a -> Ordering) -> [a] -> [a]
 
 mergesort cmp xs = merge_lists (split_into_runs [] xs)
@@ -465,6 +447,7 @@ mergesort cmp xs = merge_lists (split_into_runs [] xs)
 	  EQ  -> x : y : (merge xs ys)
 	  LT  -> x : (merge xs yl)
 	  GT -> y : (merge xl ys)
+#endif
 \end{code}
 
 %************************************************************************
@@ -556,18 +539,21 @@ balancedFold' :: (a -> a -> a) -> [a] -> [a]
 balancedFold' f (x:y:xs) = f x y : balancedFold' f xs
 balancedFold' f xs = xs
 
-generalMergeSort p [] = []
-generalMergeSort p xs = (balancedFold (generalMerge p) . map (: [])) xs
-
 generalNaturalMergeSort p [] = []
 generalNaturalMergeSort p xs = (balancedFold (generalMerge p) . group p) xs
 
+#if NOT_USED
+generalMergeSort p [] = []
+generalMergeSort p xs = (balancedFold (generalMerge p) . map (: [])) xs
+
 mergeSort, naturalMergeSort :: Ord a => [a] -> [a]
 
 mergeSort = generalMergeSort (<=)
 naturalMergeSort = generalNaturalMergeSort (<=)
 
 mergeSortLe le = generalMergeSort le
+#endif
+
 naturalMergeSortLe le = generalNaturalMergeSort le
 \end{code}
 
@@ -659,6 +645,16 @@ mapAccumB f a b (x:xs) = (a'',b'',y:ys)
 	(a'',b',ys) = mapAccumB f a' b xs
 \end{code}
 
+A strict version of foldl.
+
+\begin{code}
+foldl'        :: (a -> b -> a) -> a -> [b] -> a
+foldl' f z xs = lgo z xs
+	     where
+		lgo z []     =  z
+		lgo z (x:xs) = (lgo $! (f z x)) xs
+\end{code}
+
 A combination of foldl with zip.  It works with equal length lists.
 
 \begin{code}
@@ -676,6 +672,32 @@ count p (x:xs) | p x       = 1 + count p xs
 	       | otherwise = count p xs
 \end{code}
 
+@splitAt@, @take@, and @drop@ but with length of another
+list giving the break-off point:
+
+\begin{code}
+takeList :: [b] -> [a] -> [a]
+takeList [] _ = []
+takeList (_:xs) ls = 
+   case ls of
+     [] -> []
+     (y:ys) -> y : takeList xs ys
+
+dropList :: [b] -> [a] -> [a]
+dropList [] xs    = xs
+dropList _  xs@[] = xs
+dropList (_:xs) (_:ys) = dropList xs ys
+
+
+splitAtList :: [b] -> [a] -> ([a], [a])
+splitAtList [] xs     = ([], xs)
+splitAtList _ xs@[]   = (xs, xs)
+splitAtList (_:xs) (y:ys) = (y:ys', ys'')
+    where
+      (ys', ys'') = splitAtList xs ys
+
+\end{code}
+
 
 %************************************************************************
 %*									*
@@ -684,6 +706,22 @@ count p (x:xs) | p x       = 1 + count p xs
 %************************************************************************
 
 \begin{code}
+eqListBy :: (a->a->Bool) -> [a] -> [a] -> Bool
+eqListBy eq []     []     = True
+eqListBy eq (x:xs) (y:ys) = eq x y && eqListBy eq xs ys
+eqListBy eq xs     ys     = False
+
+equalLength :: [a] -> [b] -> Bool
+equalLength [] []         = True
+equalLength (_:xs) (_:ys) = equalLength xs ys
+equalLength xs    ys      = False
+
+compareLength :: [a] -> [b] -> Ordering
+compareLength [] []         = EQ
+compareLength (_:xs) (_:ys) = compareLength xs ys
+compareLength [] _ys        = LT
+compareLength _xs []        = GT
+
 thenCmp :: Ordering -> Ordering -> Ordering
 {-# INLINE thenCmp #-}
 thenCmp EQ   any = any
@@ -700,16 +738,22 @@ cmpList cmp (a:as) (b:bs)
 \end{code}
 
 \begin{code}
-cmpString :: String -> String -> Ordering
+prefixMatch :: Eq a => [a] -> [a] -> Bool
+prefixMatch [] _str = True
+prefixMatch _pat [] = False
+prefixMatch (p:ps) (s:ss) | p == s    = prefixMatch ps ss
+			  | otherwise = False
 
-cmpString []     []	= EQ
-cmpString (x:xs) (y:ys) = if	  x == y then cmpString xs ys
-			  else if x  < y then LT
-			  else		      GT
-cmpString []     ys	= LT
-cmpString xs     []	= GT
-\end{code}
+maybePrefixMatch :: String -> String -> Maybe String
+maybePrefixMatch []    rest = Just rest
+maybePrefixMatch (_:_) []   = Nothing
+maybePrefixMatch (p:pat) (r:rest)
+  | p == r    = maybePrefixMatch pat rest
+  | otherwise = Nothing
 
+suffixMatch :: Eq a => [a] -> [a] -> Bool
+suffixMatch pat str = prefixMatch (reverse pat) (reverse str)
+\end{code}
 
 %************************************************************************
 %*									*
@@ -720,14 +764,17 @@ cmpString xs     []	= GT
 The following are curried versions of @fst@ and @snd@.
 
 \begin{code}
+#if NOT_USED
 cfst :: a -> b -> a	-- stranal-sem only (Note)
 cfst x y = x
+#endif
 \end{code}
 
 The following provide us higher order functions that, when applied
 to a function, operate on pairs.
 
 \begin{code}
+#if NOT_USED
 applyToPair :: ((a -> c),(b -> d)) -> (a,b) -> (c,d)
 applyToPair (f,g) (x,y) = (f x, g y)
 
@@ -736,11 +783,7 @@ applyToFst f (x,y) = (f x,y)
 
 applyToSnd :: (b -> d) -> (a,b) -> (a,d)
 applyToSnd f (x,y) = (x,f y)
-
-foldPair :: (a->a->a,b->b->b) -> (a,b) -> [(a,b)] -> (a,b)
-foldPair fg ab [] = ab
-foldPair fg@(f,g) ab ((a,b):abs) = (f a u,g b v)
-		       where (u,v) = foldPair fg ab abs
+#endif
 \end{code}
 
 \begin{code}
@@ -749,26 +792,99 @@ unzipWith f pairs = map ( \ (a, b) -> f a b ) pairs
 \end{code}
 
 \begin{code}
-#if __HASKELL1__ > 4
 seqList :: [a] -> b -> b
-#else
-seqList :: (Eval a) => [a] -> b -> b
-#endif
 seqList [] b = b
 seqList (x:xs) b = x `seq` seqList xs b
+\end{code}
 
-#if __HASKELL1__ <= 4
-($!)    :: (Eval a) => (a -> b) -> a -> b
-f $! x  = x `seq` f x
-#endif
+Global variables:
+
+\begin{code}
+global :: a -> IORef a
+global a = unsafePerformIO (newIORef a)
 \end{code}
 
+Module names:
+
 \begin{code}
-#if __GLASGOW_HASKELL__ < 402
-bracket :: IO a -> (a -> IO b) -> (a -> IO c) -> IO c
-bracket before after thing = do
-  a <- before 
-  (thing a) `catch` (\err -> after a >>= fail err)
-  after a
-#endif
+looksLikeModuleName [] = False
+looksLikeModuleName (c:cs) = isUpper c && go cs
+  where go [] = True
+	go ('.':cs) = looksLikeModuleName cs
+	go (c:cs)   = (isAlphaNum c || c == '_') && go cs
+\end{code}
+
+Akin to @Prelude.words@, but sensitive to dquoted entities treating
+them as single words.
+
+\begin{code}
+toArgs :: String -> [String]
+toArgs "" = []
+toArgs s  =
+  case break (\ ch -> isSpace ch || ch == '"') (dropWhile isSpace s) of -- "
+    (w,aft) ->
+       (\ ws -> if null w then ws else w : ws) $
+       case aft of
+	 []           -> []
+	 (x:xs)
+	   | x /= '"'  -> toArgs xs
+	   | otherwise ->
+             case lex aft of
+	       ((str,rs):_) -> stripQuotes str : toArgs rs
+	       _            -> [aft]
+ where
+    -- strip away dquotes; assume first and last chars contain quotes.
+   stripQuotes :: String -> String
+   stripQuotes ('"':xs)  = init xs
+   stripQuotes xs        = xs
+\end{code}
+
+-- -----------------------------------------------------------------------------
+-- Floats
+
+\begin{code}
+readRational__ :: ReadS Rational -- NB: doesn't handle leading "-"
+readRational__ r = do 
+     (n,d,s) <- readFix r
+     (k,t)   <- readExp s
+     return ((n%1)*10^^(k-d), t)
+ where
+     readFix r = do
+	(ds,s)  <- lexDecDigits r
+	(ds',t) <- lexDotDigits s
+	return (read (ds++ds'), length ds', t)
+
+     readExp (e:s) | e `elem` "eE" = readExp' s
+     readExp s			   = return (0,s)
+
+     readExp' ('+':s) = readDec s
+     readExp' ('-':s) = do
+			(k,t) <- readDec s
+			return (-k,t)
+     readExp' s	      = readDec s
+
+     readDec s = do
+        (ds,r) <- nonnull isDigit s
+        return (foldl1 (\n d -> n * 10 + d) [ ord d - ord '0' | d <- ds ],
+                r)
+
+     lexDecDigits = nonnull isDigit
+
+     lexDotDigits ('.':s) = return (span isDigit s)
+     lexDotDigits s       = return ("",s)
+
+     nonnull p s = do (cs@(_:_),t) <- return (span p s)
+                      return (cs,t)
+
+readRational :: String -> Rational -- NB: *does* handle a leading "-"
+readRational top_s
+  = case top_s of
+      '-' : xs -> - (read_me xs)
+      xs       -> read_me xs
+  where
+    read_me s
+      = case (do { (x,"") <- readRational__ s ; return x }) of
+	  [x] -> x
+	  []  -> error ("readRational: no parse:"        ++ top_s)
+	  _   -> error ("readRational: ambiguous parse:" ++ top_s)
 \end{code}