On Sun, 26 Feb 2012 23:00:42 +0200 Alexander Batischev <eual.jp@gmail.com> wrote:

On Sun, Feb 26, 2012 at 12:31:06PM -0800, Tim Perry wrote:

...

Turn off buffering and call "words" What "words" do you mean? There's no suck function in System.IO. And if you're talking about Data.List's "words", meaning something like: getLine >>= words then it's not what I need - such a construction would consume whole line, while function I'm seeking should consume as few words as required.

Depends on what you mean by "consume". Yes, it reads the entire line into an input buffer (unless you muck with the buffering, which as has been indicated is a bad idea). The "words" function will then read that buffer, parsing it into a list of words. However, since it's all lazy, getting a single word from the list will only take a single word from the buffer, leaving the rest there to be parsed later if you ever want them. This is pretty much exactly what C's scanf function does: fills a buffer and parses as many objects out as the call requires. C is imperative, and the I/O library is built around a globally shared buffer for each file. Having functions that manipulate that buffer to parse things out of it is a reasonable solution in that context. Haskell is functional, so the I/O library is built around providing lists of characters that can be processed with Haskell's very powerful list processing facilities (or parser building tools, or ...). If you're trying to write a function that calls the non-existent scanf to get the next word, using recursion to create a loop, then add an extra parameter to the function: a list of unused words. For the first call, pass it the list from getLine >>= words (or maybe getContents, depending). Use the list primitives to get the words you need, and then pass the unused part of the list in the recursive call to process the rest of the list. Since it's all lazy, it should have the performance characteristics you want. <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/ Independent Software developer/SCM consultant, email for more information. O< ascii ribbon campaign - stop html mail - www.asciiribbon.org