[project @ 2003-08-30 23:01:48 by ross]

[haskell-directory.git] / Text / PrettyPrint / HughesPJ.hs

diff --git a/Text/PrettyPrint/HughesPJ.hs b/Text/PrettyPrint/HughesPJ.hs
index 58f098b..7e1efe2 100644 (file)
--- a/Text/PrettyPrint/HughesPJ.hs
+++ b/Text/PrettyPrint/HughesPJ.hs
@@ -251,7 +251,7 @@ rational :: Rational -> Doc
 parens       :: Doc -> Doc;    -- ^ Wrap document in @(...)@
 brackets     :: Doc -> Doc;    -- ^ Wrap document in @[...]@
 braces      :: Doc -> Doc;     -- ^ Wrap document in @{...}@
-quotes      :: Doc -> Doc;     -- ^ Wrap document in @'...'@
+quotes      :: Doc -> Doc;     -- ^ Wrap document in @\'...\'@
 doubleQuotes :: Doc -> Doc;    -- ^ Wrap document in @\"...\"@
 
 -- Combining @Doc@ values
@@ -263,6 +263,7 @@ hsep   :: [Doc] -> Doc;          -- ^List version of '<+>'
 
 ($$)   :: Doc -> Doc -> Doc;     -- ^Above; if there is no
                                 -- overlap it \"dovetails\" the two
+($+$)   :: Doc -> Doc -> Doc;   -- ^Above, without dovetailing.
 vcat   :: [Doc] -> Doc;          -- ^List version of '$$'
 
 cat    :: [Doc] -> Doc;          -- ^ Either hcat or vcat
@@ -881,6 +882,33 @@ indent n | n >= 8 = '\t' : indent (n - 8)
 multi_ch 0 ch = ""
 multi_ch n       ch = ch : multi_ch (n - 1) ch
 
-spaces 0 = ""
-spaces n       = ' ' : spaces (n - 1)
-
+-- (spaces n) generates a list of n spaces
+--
+-- It should never be called with 'n' < 0, but that can happen for reasons I don't understand
+-- Here's a test case:
+--     ncat x y = nest 4 $ cat [ x, y ]
+--     d1 = foldl1 ncat $ take 50 $ repeat $ char 'a'
+--     d2 = parens $  sep [ d1, text "+" , d1 ]
+--     main = print d2
+-- I don't feel motivated enough to find the Real Bug, so meanwhile we just test for n<=0
+spaces n | n <= 0    = ""
+        | otherwise = ' ' : spaces (n - 1)
+
+{- Comments from Johannes Waldmann about what the problem might be:
+
+   In the example above, d2 and d1 are deeply nested, but `text "+"' is not, 
+   so the layout function tries to "out-dent" it.
+   
+   when I look at the Doc values that are generated, there are lots of
+   Nest constructors with negative arguments.  see this sample output of
+   d1 (obtained with hugs, :s -u)
+   
+   tBeside (TextDetails_Chr 'a') 1 Doc_Empty) (Doc_NilAbove (Doc_Nest
+   (-241) (Doc_TextBeside (TextDetails_Chr 'a') 1 Doc_Empty)))))
+   (Doc_NilAbove (Doc_Nest (-236) (Doc_TextBeside (TextDetails_Chr 'a') 1
+   (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside (TextDetails_Chr 'a') 1
+   Doc_Empty)))))))) (Doc_NilAbove (Doc_Nest (-231) (Doc_TextBeside
+   (TextDetails_Chr 'a') 1 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside
+   (TextDetails_Chr 'a') 1 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside
+   (TextDetails_Chr 'a') 1 Doc_Empty))))))))))) (Doc_NilAbove (Doc_Nest
+-}