I understand this has nothing to do with type checking, but why can't
Super! Would be nice if this gets build into GHC/GHCI :) -----Original Message----- From: Neil Mitchell [mailto:ndmitchell@gmail.com] Sent: Wednesday, June 20, 2007 01:07 To: Felipe Almeida Lessa Cc: peterv; haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] Avoiding "Non-exhaustive patterns in function f" Hi the
compiler give a warning about this? Or is this by design or because it is impossible to check with more complex recursive data types?
Take a look at Catch from Neil Mitchell: http://www-users.cs.york.ac.uk/~ndm/catch/ .
Using the released version of Catch on the example you gave: Analysing Checking [1/1]: Main: Pattern match failure in function at 5:1-5:10. Partial: "Main.f" Partial: "Main.main" Partial: "main" Answer: 0 This says: the error message you will get is about a pattern match on line 5 (that's where 'f' is in the example program). The list of partial functions, in some kind of call-stack order, is Main.f, then Main.main - i.e. your main function calls f which is partial. Answer 0 means "the necessary precondition for safety is false" - or its not safe at all. If you turn on logging Catch will additionally tell you that the precondition on 'f' is that the data structure must be a 'A' constructed value. Thanks Neil No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.472 / Virus Database: 269.9.1/854 - Release Date: 19/06/2007 13:12 No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.472 / Virus Database: 269.9.1/854 - Release Date: 19/06/2007 13:12