On 2008 May 10, at 18:56, PR Stanley wrote:
Paul: Hi folks
data Maybe a = Nothing | Just a
What is the underlying rationale for the Maybe data type? is it the safe style of programming it encourages/ Something tells me this is going to start a lengthy discussion. :-)
Bob: Pure and simple -- it allows you to represent partial functions. Looking up a map will only sometimes find a value, so we either return Nothing, or Just that value.
Paul: Would yu like to demonstrate this in an example?
Um, I was encountering and recognizing times when I really needed an out-of-band "null", and the pain of representing such in C, shortly after I started serious programming in C (call it 1984-5). Is this really difficult? -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH