* Luke Palmer <lrpalmer@gmail.com> [2009-01-03 18:46:50 -0700]:

> 2009/1/3 Xie Hanjian <jan.h.xie@gmail.com>
>
> > Hi,
> >
> > I tried this in ghci:
> > >Prelude> 1:2:[] == 1:2:[]
> > True
> >
> > Does this mean (:) return the same object on same input,
>
>
> Also, in functional programming, *every* function returns the same output
> for the same input. That's part of the definition of function. :-)

This is true in Haskell, but may not true in Scheme (I guess also false
in Lisp).

I, like many arrogant Haskellers, reject Scheme and other such impure languages as "functional". At least until I turn on my brain.

So, revise the beginning of my statement to "Also, in pure functional programming, ..."

Luke

In DrScheme:

>(eq? (cons 1 2) (cons 1 2))
#f
>(equal? (cons 1 2) (cons 1 2))
#t

Although equal? treats the two as the *same*, they're different lists
because if we modify one (e.g by set-car!) the other won't be affected.

So here comes another question: when we say a function always give the
same output for the same input, what the *same* means here? ídentity
or equality?

Thanks
Jan

>
> Luke

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