[Haskell-cafe] Maybe a, The Rationale

[Thomas Davie]

On 11 May 2008, at 00:36, PR Stanley wrote:

> 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. :-)

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.

Bob