Re: Haskell Wish list: library documentation

[Jon . Fairbairn]

On  9 Sep, George Russell wrote:
> Here is my revised version of the documentation.  
          my :-) (which incorporates some of the other suggestions.)
I've given reasons at the bottom.

Type:

> unzip :: [(a,b)] -> ([a],[b])

unzip takes a list of pairs and returns a pair of lists.

Definition:

> unzip l = (map fst l, map snd l)                            --  [1]

Description:

see zip;  unzip is such that if 
                unzip l = (a, b)
          then  zip a b = l                                   --  [2]

Examples:

   unzip [(1, 4), (2, 5), (3, 6)] = ([1, 2, 3], [4, 5, 6])    --  [3]

See Also: unzip3


Notes about the above:

[1] The prelude is supposed to give definitions that are semantically
    correct but are not necessarily efficient (eg sort), and I think
    this is clearer.  There are other definitions in the prelude that
    could be made easier to understand.

[2] the motivation for the name comes from zip, and it makes it harder
    to describe unzip when it's only necessarily true that zip undoes
    what unzip does, and not vice versa.

[3] I think this example is slightly easier, though on second thoughts

    unzip [('a', 1), ('b', 2), ('c', 3)] = (['a', 'b', 'c'], [1, 2, 3])

    is better still.


Unrelated whinge:

    I missed the discussion that decided that show should omit the
    syntactically unnecessary spaces when converting lists and tuples.
    While this may save space in files, I don't see that we are
    equipped to break with centuries of typographic tradition wrt
    spaces and commas.

-- 
Jón Fairbairn                                 [EMAIL PROTECTED]