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OK, I took some time to mock out some Scheme: here are both behaviours you've seen:

(define cclosures (lambda (values) (cond ((null? values) '()) (else (cons (lambda (x) (* (car values) x)) (cclosures (cdr values))))))) (define cclosures2 (let ((val -1)) (lambda (values) (cond ((null? values) '()) (else (begin (set! val (car values)) (cons (lambda (x) (* val x)) (cclosures2 (cdr values))))))))) (define clprint (lambda (closures) (map (lambda (fn) (fn 2)) closures))) > (clprint (cclosures '(0 1 2))) (0 2 4) > (clprint (cclosures2 '(0 1 2))) (4 4 4)

cclosures uses the equivalent ofdeclaring my $i inside the foreach loop: it defines a new variable called val for every iteration.

cclosures2 uses the equivalent of declaring my $i outside the foreach loop: val gets reassigned with every iteration.

Notice the closure closes over the variable, not the value. So when the variable is reassigned, the value inside the closure changes too.

HTH


In reply to Re^4: Lexical closures by mpeever
in thread Lexical closures by spurperl

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