Re: Appropriate methods for argument checking

chase@centerline.com (David Chase) writes:
> If you use parametric polymorphism, the variable type is actually polymorphic:


> T (*f)(T) <type T> = f_of_char_yielding_char;
> T (*f)(T) <type T> = f_of_short_yielding_short;


No; the only if f has the above type then it must accept arguments of any
type (and return a result of the same type). In many type theories, the
only such function is the polymorphic identity function. The lack of
polymorphism in traditional languages like Pascal, etc. means that the
programmer would be forced to write seperate definitions for the boolean
identity function, the integer identity function, etc. even though the
bodies would be identical.


The identity function may seem like a useless example; however consider a
similar situation where the programmer has to write seperate sort functions
for arrays of integers, arrays of floats, arrays of strings, etc. Modern
functional languages which support polymorphism (such as Haskell or SML)
solve this and similar problems very elegantly.


<snip further comments on parametric polymorphism>


I'm not really sure, but it looks like you're confusing
parametric polymorphism with existential types. I.e.
you seem to be referring to (using your C syntax)
T (*f)(T) <for some type T>
rather than parametric polymorphism or
T (*f)(T) <for all types T>


Cheers, Dara. --
_______________________________________________________________
Dara Gallagher. http://www.cs.tcd.ie/www/jgllgher/jgllgher.html
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