On Tuesday, 2003-08-19, 12:42, CEST, Konrad Hinsen wrote: > I have been following the recent "Monad tutorial" discussion with interest, > and even read the tutorial, which is a useful addition to the existing > Haskell documentation. So useful in fact that it raises a question... > > The whole monad mechanism seems to geared towards functions of one argument, > plus eventually state, that get chained together. How about functions with > several arguments? > > As an example, I'll use the Maybe monad. Suppose I want to write code to > handle experimental data, in which there might be missing values. I might > then decide to represent measurements by data of type "Maybe Double", with > missing values represented by "Nothing". I could then go on to define > functions on missing values, which would return "Nothing" when their > argument is "Nothing", and I could string these functions together via the > monad mechanism. Fine. But how would I handle e.g. addition of two such > values? The result should be "Nothing" when either of its arguments is > "Nothing". Is there any mechanism to handle that?
Yes, liftM2. Defined in module Monad (or Data.Monad resp.). > Konrad. Wolfgang _______________________________________________ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
