[Haskell-cafe] Maybe a, The Rationale

[Brandon S. Allbery KF8NH]

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 at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH