Re: Using cl-case on symbols

Heime <[email protected]> writes:

> It has been suggested to me about using the following `cl-case'
> construct for checking ACTM against a list of symbols.  With `cond' I
> would have to use ((or (eq actm 'add) (eq actm 'remove))
>
> How is it that `cond' does not work on symbols but `cl-case' does?

`cond' works with everything because you define the complete condition
yourself.  E.g.,

  (cond
    ((> i 17) 'i-is-greater-than-17)
    (t        'i-is-something-else))

`cl-case' is more specialized.  It only tests for equality or set
membership using `eql'/`memql'.  So the above greater-than test is not
feasible to express with `cl-case' (well, unless you write a clause with
a list containing all numbers > 17 of which there are many).

> Although I have looked at the documentation of `cl-case', there is
> no indication on its appropriateness to symbols.  

As said above, `cl-case' uses `eql' for comparison.  Two interned
symbols with the same name are `eq' so they are `eql', too.  Keywords
can also be compared with `eq' (and thus `eql').  And numbers can be
compared with `eql'.  So these are the types suitable for a `cl-case'
expression.  For example, strings are NOT suited.

HTH,
Tassilo