A quick analogy:
A "co-expression" is like flash-freezing an expression and sticking it in
the freezer for later use.
So, when you say
function(1 to 10), that evaluates the generator "1 to 10" right there
place when the function is called and the function is called, possibly
multiple times, with a single number as a parameter.
But, if you say
function(create(1 to 10))
or almost equivalently*
function{1 to 10}
Then the whole generator "1 to 10" is wrapped in dry ice, packed up in a
box and sent to the function.
Then you can get values from the generator, 1 at a time, using the @
operator, which you can think of as thawing the expression enough to get
out one value, and sticking it back in the freezer.
So:
function(create(1 to 10))
...
procedure function(coexpr)
while n := @coexpr do {
write(n)
}
end
writes:
1
2
3
4
5
6
7
8
9
10
Hope this helps,
Louis
* the {} syntax sticks all the parameters into an array, otherwise it is
equivalent.
On Wed, 29 Oct 2003, Hiroshi Shinohara wrote:
>
> Steve >While the above works, that's actually quite a bit of
> Steve >work that using a co-expression as Louis suggested
> Steve >avoids. In fact, your problem is a good fit for
> Steve >a PDCO, (which can be thought of as fancy syntax
> Steve >to avoid writing 'create'...):
>
> Chap 9. Co-Expression is one of chapters I cannot understand
> in "The Icon Programming Languge".
>
> I'll try to understand Co-Expression again.
>
> Thanks,
> Hiroshi Shinohara
>
>
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