To whom it may concern:
I am using Hugs98 (september release) together with the pretty printer
combinators by Hughes and Jones.
When printing a large structure, Hugs aborts with the message GC
Blackhole. The program works fine for smaller structures.
The problem occurs with all renderes.
I am quite sure that this is a pretty printing problem because the program
works fine when using a simple derived Show instance.
The problem occurs with ghc 4.05 , too. When printing a large structure,
the program crashes due to a bus error.
In order to reproduce the error you will need the complete package
including test data. (I could not reproduce the error by command-line
generated test data.) I will send a tar.gz file on demand.
I attached the module which makes use of the combinators. Maybe there is
an error.
Thank you,
Michael Marte
module Prolog(Term(..), Fact(..)) where
import Pretty
import List
data Term =
Atom String |
Int Int |
Var String |
AnonVar |
Tuple [Term] |
List [Term] |
Set [Term] |
Struct String [Term]
newtype Fact = Fact Term
instance Show Term where
show t = show (pretty t)
instance Show Fact where
show (Fact t) = show ((pretty t) <> (text "."))
pretty (Atom a) = text a
pretty (Int i) = int i
pretty (Var id) = text id
pretty AnonVar = text "_"
pretty (Tuple ts) = parens (fsep (punctuate comma (map pretty ts)))
pretty (List ts) = brackets (fsep (punctuate comma (map pretty ts)))
pretty (Set ts) = braces (fsep (punctuate comma (map pretty ts)))
pretty (Struct f ts) = (text f) <> (parens (sep (punctuate comma (map pretty ts))))
oneLineProlog :: Doc -> String
oneLineProlog d = fullRender OneLineMode 0 0 stringHandler "" d
stringHandler :: TextDetails -> String -> String
stringHandler (Chr c) s = c:s
stringHandler (Str s1) s2 = s1 ++ s2
stringHandler (PStr s1) s2 = s1 ++ s2
