RE: [boost] Re: Review Request: FC++

From: David Bergman (davidb_at_[hidden])
Date: 2003-10-21 11:51:31

Dave wrote: 

> "David Bergman" <davidb_at_[hidden]> writes:
> 
> > It has to do with purity, that Haskell is a pure language 
> in the sense 
> > of an expression ALWAYS evaluating to the same value, so 
> that the same 
> > exact expression can be substituted for that computed value 
> wherever, whenever.
> 
> Even I can tell that has no bearing on side-effects, though:
> 
>   int z;
>   int f(int x) { return z = x; }
> 
> f(y) is always y for any y
> still, it has side-effects.

Good, than that particular expression is transparent, in the pure sense. If
you manage to have *all other* expressions being transparent as well, you
have a pure piece of code! (That would of course mean that the side-effect
in your assignment is *never* exposed...)

"Side effect" indicates that it should affect the visible parts of the
execution, just like in the operational abstract machine in the C++
language, does it not? Writing to a memory cell which is never read is
hardly a side-effect, is it?

/David