Comments on: Fun with Haskell view patterns http://www.serpentine.com/blog/2009/01/11/fun-with-haskell-view-patterns/ Bryan O'Sullivan's blog Wed, 08 Feb 2012 06:41:38 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Twan van Laarhoven http://www.serpentine.com/blog/2009/01/11/fun-with-haskell-view-patterns/comment-page-1/#comment-201523 Twan van Laarhoven Sun, 11 Jan 2009 16:11:30 +0000 http://www.serpentine.com/blog/?p=318#comment-201523 Instead of writing your own 'dropPrefix', there is also the standard 'stripPrefix :: Eq a => [a] -> [a] -> Maybe [a]', which you can also use with view patterns: {-# LANGUAGE ViewPatterns #-} genbankHeader (stripPrefix ">gi|" -> Just rest) = muddle rest Instead of writing your own ‘dropPrefix’, there is also the standard ‘stripPrefix :: Eq a => [a] -> [a] -> Maybe [a]‘, which you can also use with view patterns:

{-# LANGUAGE ViewPatterns #-}
genbankHeader (stripPrefix “>gi|” -> Just rest) = muddle rest

]]> By: Bryan O'Sullivan http://www.serpentine.com/blog/2009/01/11/fun-with-haskell-view-patterns/comment-page-1/#comment-201522 Bryan O'Sullivan Sun, 11 Jan 2009 15:57:14 +0000 http://www.serpentine.com/blog/?p=318#comment-201522 Oops, thanks for noticing those thinkos, gentlemen. That's what I get for composing a post at midnight! Oops, thanks for noticing those thinkos, gentlemen. That’s what I get for composing a post at midnight!

]]> By: Alf http://www.serpentine.com/blog/2009/01/11/fun-with-haskell-view-patterns/comment-page-1/#comment-201520 Alf Sun, 11 Jan 2009 15:20:02 +0000 http://www.serpentine.com/blog/?p=318#comment-201520 Marc: presumably 'after' was the original name of dropPrefix. Rename it, and the function starts working. The 'otherwise' line is unnecessary, btw. Marc: presumably ‘after’ was the original name of dropPrefix. Rename it, and the function starts working.

The ‘otherwise’ line is unnecessary, btw.

]]> By: Marc http://www.serpentine.com/blog/2009/01/11/fun-with-haskell-view-patterns/comment-page-1/#comment-201514 Marc Sun, 11 Jan 2009 12:31:23 +0000 http://www.serpentine.com/blog/?p=318#comment-201514 I don't know about newer GHCs, but in 6.8.1, dropPrefix "foo" "foobar" gives a pattern match error (since left becomes [] after some time). Also, what is the "after" function for? I don’t know about newer GHCs, but in 6.8.1, dropPrefix “foo” “foobar” gives a pattern match error (since left becomes [] after some time).
Also, what is the “after” function for?

]]> By: Joachim Breitner http://www.serpentine.com/blog/2009/01/11/fun-with-haskell-view-patterns/comment-page-1/#comment-201507 Joachim Breitner Sun, 11 Jan 2009 11:15:33 +0000 http://www.serpentine.com/blog/?p=318#comment-201507 Is there a copy’n’paste error in Prelude> dropPrefix "foolish" "football" ("lish", "ball") which should rather be Prelude> dropPrefix "foolish" "football" ("lish", "tball") ? Is there a copy’n’paste error in
Prelude> dropPrefix “foolish” “football”
(“lish”, “ball”)
which should rather be
Prelude> dropPrefix “foolish” “football”
(“lish”, “tball”)
?

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