I agree that's odd. Are you using -O? Can you give us a reproducible test case? (The only think I can think is that the line | Gc{} -> Tm (grspe r) will build a thunk for (grspe r), and depending on the context I suppose you might get a lot of those.) Thanks Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users- | bounces@haskell.org] On Behalf Of Han Joosten | Sent: 12 January 2009 21:54 | To: glasgow-haskell-users@haskell.org | Subject: Differences in pattern matching syntax? | | | Hi, | | I have two alternatives to specify a specific function. They both compile | ok, but the first one crashes (Stack space overflow) while the second one | runs fine. | I use GHC 6.10.1 on windowsXP | | Alternative 1: | antecedent :: Rule -> Expression | antecedent r = case r of | Ru{} -> if (rrsrt r == AlwaysExpr) then error ("(Module | ADLdataDef:) illegal call to antecedent of rule "++show r) | else | rrant r | Sg{} -> antecedent (srsig r) | Gc{} -> Tm (grspe r) | Fr{} -> frcmp r | | Alternative 2: | antecedent :: Rule -> Expression | antecedent r@(Ru AlwaysExpr _ _ _ _ _ _ _ _) = error ("(Module ADLdef:) | illegal call to antecedent of rule "++show r) | antecedent (Ru _ a _ _ _ _ _ _ _) = a | antecedent (Sg _ rule _ _ _ _ _) = antecedent rule | antecedent (Gc _ d _ _ _ _ _) = Tm d | antecedent (Fr _ _ e _) = e | | Both alternatives compile, but if i use Alternative 2, then my program runs | fine. If I use Alternative 1 instead, I get a stack space overflow. | | I would think that both alternatives would have the same semantics. So i am | surprised that one runs fine, while the other one crashes. | | Could anyone explain what is going on? | Thanks! | | Han Joosten | | ---------------------------- | Might help, here is the data definition: | | data Rule = | -- Ru c antc p cons cpu expla sgn nr pn | Ru { rrsrt :: RuleType -- ^ One of the following: | -- | Implication if this is an | implication; | -- | Equivalence if this is an | equivalence; | -- | AlwaysExpr if this is an | ALWAYS expression. | , rrant :: Expression -- ^ Antecedent | , rrfps :: FilePos -- ^ Position in the ADL file | , rrcon :: Expression -- ^ Consequent | , r_cpu :: Expressions -- ^ This is a list of | subexpressions, which must be computed. | , rrxpl :: String -- ^ Explanation | , rrtyp :: (Concept,Concept) -- ^ Sign of this rule | , runum :: Int -- ^ Rule number | , r_pat :: String -- ^ Name of pattern in which it was | defined. | } | -- Sg p rule expla sgn nr pn signal | | Sg { srfps :: FilePos -- ^ position in the ADL file | , srsig :: Rule -- ^ the rule to be signalled | , srxpl :: String -- ^ explanation | , srtyp :: (Concept,Concept) -- ^ type | , runum :: Int -- ^ rule number | , r_pat :: String -- ^ name of pattern in which it was | defined. | , srrel :: Declaration -- ^ the signal relation | } | -- Gc p antc cons cpu _ _ _ | | Gc { grfps :: FilePos -- ^ position in the ADL file | , grspe :: Morphism -- ^ specific | , grgen :: Expression -- ^ generic | , r_cpu :: Expressions -- ^ This is a list of | subexpressions, which must be computed. | , grtyp :: (Concept,Concept) -- ^ declaration | , runum :: Int -- ^ rule number | , r_pat :: String -- ^ name of pattern in which it was | defined. | } | -- Fr t d expr pn -- represents an automatic computation, such as * or +. | | Fr { fraut :: AutType -- ^ the type of automatic | computation | , frdec :: Declaration -- ^ where the result is to be | stored | , frcmp :: Expression -- ^ expression to be computed | , frpat :: String -- ^ name of pattern in which it was | defined. | } | | -- | View this message in context: http://www.nabble.com/Differences-in-pattern-matching-syntax-- | tp21416338p21416338.html | Sent from the Haskell - Glasgow-haskell-users mailing list archive at Nabble.com. | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users