Adding to other replies:
At Thu, 20 Jul 2017 13:32:49 -0400, David Storrs wrote:
> Will any of the above items be compiled away?
You can compile a module with `raco make` and look at the compiled code
with `raco decompile`. If I put your code in a module and try that, the
output includes
(define-values
(_foo)
(lambda ()
....
(begin
(values (file-size '"/some/path"))
(let ((local22 (file-size '"/some/other/path")))
(begin
(|_displayln:p@(lib "racket/private/misc.rkt")|
(#%sfs-clear local22))
'#t)))))
So, you can see that the compiler discarded an addition that always
produces 2, and it discarded the unused `bar` function. It also got rid
of the unused `size` variable, but it preserved everything else as a
run-time computation.
> Perl has the 'state' declaration, which says "Declare this as a local
> variable, but keep it around with its value preserved after you exit the
> function."
Assuming that you really want to do that and you really want a `state`
form:
(define-syntax (state stx)
(syntax-parse stx
[(_ var:id rhs:expr)
(with-syntax ([lifted-var (syntax-local-lift-expression #'rhs)])
#'(define-syntax var (make-rename-transformer #'lifted-var)))]))
(define (f v)
(state accum 0)
(set! accum (+ v accum))
accum)
(f 1)
(f 2)
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