Hi, I have just a short question, about the semantics of Implicit parameters on GHC 6.4.
Given the following code: > (???) x f > = let ?foo = 1337 > in f x > fun :: (?foo::Int,Show x) => x -> String > fun x = "x = "++(show x)++"; ?foo = "++(show ?foo) > test = let ?foo = 23 > in 42 ??? fun I would expect: test == "x = 42; ?foo = 1337" Because I thought, that it gets reduced like: let ?foo = 23 in 42 ??? fun ~> let ?foo = 23 in (let ?foo = 1337 in fun 42) ~> ... ~> "x = 42; ?foo = 1337" however I get "x = 42; ?foo = 23" in ghci. Is there a special reason, why the implicit parameter is reduced first? Could it be a bug? Reducing it my way would be very useful for combinator-libraries, since it could be used passing around state info, or simple debug text, that tells where a Runtime-error occured? an odd example: > undef = error ?errstr > (<?>) x s = let ?errstr = ?errstr++"\n"++s in x -- annotate error tags so error annotations will accumulate and it would be easy to resolve runtime errors. best regards Eike Scholz _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
