Re: [racket-users] exercise 1, racket school 2018
On 6/17/19 4:20 PM, Robert Girault wrote: I was able to do the first half of exercise 1 (see sources at the end of this message) --- write a macro computing some information at run-time. The second half is to write the same macro, but computing some information at compile-time --- I couldn't do this one. I'm looking for some directions on how to achieve this. (*) Context ; Syntax -> Syntax ; (define-world* name ...) defines all name ... to stand for a string (define-syntax (define-world* stx) (syntax-parse stx ((_ x:id ...) #'(define-values (x ...) (values (begin 'x "world") ...) (*) Exercise 1 Exercise 1. Modify define-world* so that it binds each given identifier to its place in the sequence. We start counting at 0 so that (define-world* x y z) binds x to 0, y to 1, and so on. Hint 1: If you were going to translate this one example by hand, here's one way to do it: (define-values (x y z) (values 0 1 2)) Hint 2: Here's another way to do it: (begin (define x 0) (define y 1) (define z 2)) Why might the first version be "better" than the second version (from a macro-writer's point of view, at least)? Ryan -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/9aa7b28d-97db-43aa-46a4-336683cce65f%40ccs.neu.edu. For more options, visit https://groups.google.com/d/optout.
[racket-users] exercise 1, racket school 2018
I was able to do the first half of exercise 1 (see sources at the end of this message) --- write a macro computing some information at run-time. The second half is to write the same macro, but computing some information at compile-time --- I couldn't do this one. I'm looking for some directions on how to achieve this. (*) Context ; Syntax -> Syntax ; (define-world* name ...) defines all name ... to stand for a string (define-syntax (define-world* stx) (syntax-parse stx ((_ x:id ...) #'(define-values (x ...) (values (begin 'x "world") ...) (*) Exercise 1 Exercise 1. Modify define-world* so that it binds each given identifier to its place in the sequence. We start counting at 0 so that (define-world* x y z) binds x to 0, y to 1, and so on. Consider two variants: one that compiles the values at compile time and another one that computes them at run time. The second one might be a bit easier, but do try your hands at both. (*) My first solution ; Syntax -> Syntax ; (define-naturals-runtime* ...) defines all names ... each to natural ; number beginning at 0 (we use a counter computed at runtime). (define-syntax (define-naturals-runtime* stx) (syntax-parse stx ((_ x:id ...) #'(begin (define n -1) (begin (set! n (add1 n)) (define x n)) ... (*) Compile-time version That's my trouble. Here's what I wrote. (define-syntax (define-naturals* stx) (define n -1) (syntax-parse stx ((_ x:id ...) #`(begin (begin #,(set! n (add1 n)) (define x #,n)) ... > (syntax->datum (expand-once '(define-naturals* a b c))) '(begin (begin # (define a 0)) (begin # (define b 0)) (begin # (define c 0))) I see (set! n (add1 n)) took place once --- at compile-time. I expected something like: '(begin (begin # (define a 0) (set! n 1)) (begin # (define b 1) (set! n 2)) (begin # (define c 2) (set! n 3))) I think I don't understand the real definition of "...". Thank you. Sources: https://summer-school.racket-lang.org/2018/plan/mon-mor-lecture.html https://summer-school.racket-lang.org/2018/plan/mon-mor-lab.html -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAH-HXu_JzMdHGy29RFUqdeR81%3DfJcAK6T%2BN0EK-PdO%3D6tzk__A%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
