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February 2003

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RE: [Template-haskell] The ':' operation with patterns ?
by Simon Peyton-Jones 06 Feb '03

06 Feb '03

I've been chasing this TH bug down. There are two issues. One is the question of pattern splices, which I'll put in a separate email. However, Sean's suggestion: pcons x xs = pcon "GHC.Base::" [x,xs] should have worked fine, and didn't. (The form Foo:baz is an "original name" for the thing.) The failure turned out to be a consequence of the fact that the Exp data type in THSyntax says; data Exp = Var String | Con String | ... | Infix (Maybe Exp) String (Maybe Exp) | ... The String was assumed to be the name of a variable, not a data constructor. So GHC looked it up in a different name space than the namespace of constructors. Notice, in contrast, that Exp distinguishes Var and Con occurrences all by themselves. This inconsistency led to the bug. For now, I have changed Exp to say Infix (Maybe Exp) Exp (Maybe Exp) where the operator is expected to be either "Var s" or "Con s". Not ideal, but it'll make it all work again, I think. OK, so now it works. A bit of a wild goose chase. I attach working Zip and Main files. Simon | -----Original Message----- | From: Alain Cremieux [mailto:alcremi@pobox.com] | Sent: 26 January 2003 22:07 | To: template-haskell(a)haskell.org | Subject: [Template-haskell] The ':' operation with patterns ? | | Hi, | | I'm trying to code the exemples of "Template Meta-Programming" for | Haskell. Since there are differences in the implementation, I'm obliged | to understand what I code, which is a good exercise. | | At present I'm stuck in the mkZip function, because I'm unable to create | a pattern which is a list concatenation of 2 patterns. | For expressions I can use 'listExp', but what is the equivalent for | patterns ? | | the code : | | -- call : $(zipN 3) as bs cs | | zipN :: Int -> Expr | zipN n | | (n <= 0) | = fail "Incorrect arg to 'zipN' - zipN n, n >= 1" | | otherwise | = [| let zp = $(mkZip n [| zp |]) | in zp |] | | mkZip :: Int -> Expr -> Expr | mkZip n name = lam pYs (caseE (tup eYs) [m1, m2]) | where | pXs, pYs, pXSs :: [Patt] | eXs, eYs, eXSs :: [Expr] | (pXs, eXs) = genPE "x" n -- x1, x2,... | (pYs, eYs) = genPE "y" n -- y1, y2,... | (pXSs, eXSs) = genPE "xs" n -- xs1, xs2,... | --pcons x xs = [p| $x : $xs |] | pcons :: Patt -> Patt -> Patt | pcons x xs = ptup (x : [xs]) -- NOT correct, gives (x, xs) | instead of x : xs | b :: Expr -- ((x1, x2,...) : (zp xs1 xs2 ...)) | b = listExp [tup eXs, apps (name : eXSs)] | m1 :: Mtch -- ((x1:xs1), (x2:xs2),...) -> ((x1, x2,...) : (zp | xs1 xs2 ...)) | m1 = alt (ptup (zipWith pcons pXs pXSs)) b | m2 :: Mtch -- (_, _,...) -> [] | m2 = alt (ptup (replicate n pwild)) (listExp []) | | -- alt = (a1, a2, ..., an) -> ai -- the match part of a case clause | (just an example) | alt :: Patt -> Expr -> Mtch | alt p e = | do x <- e | return (Mat p (Normal x) []) | | Thanks, | Alain | | _______________________________________________ | template-haskell mailing list | template-haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell

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RE: [Template-haskell] A subtle bug with GHC
by Simon Peyton-Jones 06 Feb '03

06 Feb '03

I believe I have fixed this problem. The current HEAD has the fix. Thanks for reporting it -- sorry for slow service! Simon | -----Original Message----- | From: Sean Seefried [mailto:seefried@itee.uq.edu.au] | Sent: 20 January 2003 05:28 | To: template-haskell(a)haskell.org | Subject: [Template-haskell] A subtle bug with GHC | | I've noticed a subtle bug with TH. It took me some time to realise what | was happening. First I will present my source files. | | --- [Splices.hs] ---- | module Splices where | | import Char | import Language.Haskell.THSyntax | | debug f = [| do { putStrLn (show ( $(f) + 3)) ; | putStrLn "Hello World!" } |] | | ---------------------------- | --- [ Main.hs] --------- | | module Main where | | import Language.Haskell.THSyntax | import Splices | | main = $(debug [| (1::Integer) |]) | ----------------------------- | | When I compile this from scratch using the command line: | | prompt> ghc --make -fglasgow-exts -package haskell-src -package | haskell98 Main.hs -o test | | we get | | prompt> | Chasing modules from: Main.hs | Compiling Splices ( Splices.hs, ./Splices.o ) | Compiling Main ( Main.hs, ./Main.o ) | Loading package base ... linking ... done. | Loading package haskell98 ... linking ... done. | Loading package haskell-src ... linking ... done. | Linking ... | | And the program works as expected. But I noticed that when I made a | small change to Main.hs and recompiled the following would occur: | | Skipping Splices ( Splices.hs, ./Splices.o ) | Compiling Main ( Main.hs, ./Main.o ) | Loading package base ... linking ... done. | Loading package haskell98 ... linking ... done. | Loading package haskell-src ... linking ... done. | | No instance for (Monad IO) | arising from a do statement at <compiler-generated-code> | In a right-hand side of function `main': | $[splice](debug [| (1 :: Integer) |]) | In the definition of `main': | main = $[splice](debug [| (1 :: Integer) |]) | make: *** [all] Error 1 | | | I can repeat this error at will. As long as Splices.hi and Splices.o | are in existence the above error will occur when trying to recompile | Main.hs. | | I was using ghc-5.05.20030118 | | Sean Seefried | | _______________________________________________ | template-haskell mailing list | template-haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell

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