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beginner's questions - fix f
by Bob Koutsky 03 Jan '70

03 Jan '70

Hello, After watching members of this list discussing some for me really incomprehensible details of Haskell standard, I feel sort of silly for asking something probably very basic, but I'd be very grateful for any answer: Some time ago, I have decided to educate myself in functional programming, and I choose Haskell as a language of choice. I purchased "Haskell school of expression" and began to study it. Everything went well, I understood (at least intuitively) everything, but then, suddenly, I hit a wall: ------------------------------------------------------------ Exercise 9.9: remainder a b = if a < b then a else remainder (a-b) b fix f = f (fix f) Rewrite remainder using fix so that it is not recursive. ------------------------------------------------------------ Function fix left me completely puzzled. With help of hugs I found out that its type is "( a -> a ) -> a", but I have absolutely no idea how it could be used to do anything useful. It seems to me that argument to f on the right side of fix's definition must always evaluate to the same value, no matter how deep the recursion is, so there is no point to use it. I guess I am missing something very obvious, but what is it? Can somebody provide me with an example how to use fix for something just a bit useful, if possible to rewrite remainder? thank you, Bob Koutsky

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