knyttr wrote:
1. suppose I have a function like this
fun x y z = ... fun x y [] = ... fun x [] [] = ... where ...
the "where" term will be applied just to the last definition. is it possible to force it to all "fun" definitions?
The last two parts of your definition of fun will never be reached. The order of the definition is relevant. The first 'match' will be used. In this case, even if the third parameter of fun is an empty list, the part fun x y z =... is a match. In this case, changing the order to fun x [] [] = ... fun x y [] = ... fun x y z = ... would make more sence. however, there still is overlap. (ghc could generate a warning for this) now the where part: there are several options: fun x y z | z == [] = ... | y == [] = ... | otherwise = ... where ... or using a case expression... fun x y z = case (x,y,z) of (_ , _ , []) -> ... (_ , [] , [_:_]) -> ... (_ , [_:_], [_:_]) -> ... where ... pattern matches do not overlap this way. you could use this pattern matches also in the previous solution. Then your second question:
2. how can I change a field in a list in the most easy way? the only solution I found is below. I am not very happy with it - it does too many operations just to change one field.
changeIn array index value = (take (index-1) array)++[value]++(drop index array)
Remember, in haskell you do not 'change' values in variables. Thers is no such thing as a variable. You probably want a function that takes a list, an index and a value. It produces a list with all elements from the first list, only the n-th element is replaced with the given value. I would specify this as follows: f x:xs i v | i == 1 = v:xs | i > 1 = x : (f xs (i-1) v) but there are probably dozens of other ways to do this. While you are new to Haskell, do not worry too much about performance. (ghc will surly surprise you =^D) The main thing is to think functions. If you do that, you will appreciate Haskell for sure. -- View this message in context: http://old.nabble.com/begginers%27-questions-tp27377905p27378623.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.