[clean-list] Re: no deriving Eq in Clean? / toString badness

[Ben Lippmeier]

Paul,

Thanks for answering my question.

It turns out that the Linux binary distribution I got from the Clean 
web-site did not include the Generics library. I had to download the 
Windows version and copy the files across. I also had to grab the 
StdGeneric.icl (.dcl) from the Windows distribution and copy it to 
$(clean)/stdenv for this to work..

Then it turns out that you have to provide the instance for (==) anyway 
otherwise utility functions (lookup, find, .. ) stop working.. my code 
now contains lots of snippets like the following...

derive gEq SomeType
instance ==  SomeType where
 (==) a b    = a === b

It's curious that you would choose to use (===) over (==) for the more 
common equality (at least from the programmers perspective) .. though I 
suppose that generics were added after the old (==) was in common use.

------------------

Continuing on the "toInt badness" thread,

("'" +++ toString [1, 2, 3] +++ "'")  produces simply "''"


in StdList.icl

    instance toString [x] | toChar x

As toChar for lists does a direct ascii conversion, you end up with a 
set of control characters instead of what you intended. .. _even though_ 
(toString 3) gives you the 'correct' answer "3"..

.. perhaps someone should take note of "the principle of least surprise" 
? :)

.. it's a good thing I REALLY want to write this program in Clean.. a 
lesser man might have given up by now.

Ben.

------------------------

Paul de Mast wrote:

>You may use Clean genercis for this.
>
>In {Clean 2.1.0}\Libraries\Generics 0.2 you can find GenEq.dcl and GenEq.icl. This module defines an === operator.
>  
>
>  
>