Differences in pattern matching syntax?

[Han Joosten]

Hi,

I do not use -O to compile, as far as I know. I use eclipsefp and I use the
defaults from it. 
I will upload my modules as a zip file, so you can reproduce the error. It
also contains a README.txt file that explains how to reproduce it. 
Hope that helps.
http://www.nabble.com/file/p21439653/src.zip src.zip 


Simon Peyton-Jones wrote:
> 
> 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 at haskell.org
> [mailto:glasgow-haskell-users-
> | bounces at haskell.org] On Behalf Of Han Joosten
> | Sent: 12 January 2009 21:54
> | To: glasgow-haskell-users at 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.
> |            }
> |
> | --
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> | tp21416338p21416338.html
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> |
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