On Fri, Jun 13, 2008 at 01:14:04PM +1000, konrad Zielinski wrote:
> I've been trying to get my head around how closures work in Pico lisp.
As PicoLisp uses dynamic binding, there are no _direct_ static lexical
clausures. As in other cases too, the programmer has to (or better: can)
control things directly.
There are several functions to control dynamic environments, like 'bind'
or 'job'.
> specifically how would I set up a variable a function which returns
> successive integers each time it is called.
I would use 'job' here
(de counter ()
(job '((Cnt . 0))
(inc 'Cnt) ) )
You supply a list of variables (here 'Cnt') and initial values (here
'0') to 'job', and a runtime body.
: (counter)
-> 1
: (counter)
-> 2
If you inspect this function
: (pp 'counter)
(de counter NIL
(job '((Cnt . 2)) (inc 'Cnt)) )
You see that the explicit environment is maintained by 'job'. During the
execution of the runtime body (inc 'Cnt), the variables are dynamically
bound to their values, and saved thereafter.
> My first Idea was to return this form anther function but it didn't work
You can this, too. The 'curry' function employs 'job' in certain cases
(de make-counter (InitialValue @Increment)
(curry (@Increment InitialValue) ()
(inc 'InitialValue @Increment) ) )
Calling 'make-counter' returns a new function
: (make-counter 0 1)
-> (NIL (job '((InitialValue . 0)) (inc 'InitialValue 1)))
which is basically the same as our counter above.
: (def 'counter (make-counter 0 1))
-> counter
: (counter)
-> 1
: (counter)
-> 2
Cheers,
- Alex
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