---- Hans Aberg <haber...@telia.com> wrote: > What is the practical difference between the two ways of doing the same thing > (letrec or an environment). Is letrec more efficient in the implementation of > Guile? > > Hans > > > (letrec ( > (even? (lambda (n) > (if (zero? n) #t (odd? (- n 1))))) > (odd? (lambda (n) > (if (zero? n) #f (even? (- n 1)))))) > (even? 1000)) > > ((lambda () > (define even? (lambda (n) > (if (zero? n) #t (odd? (- n 1))))) > (define odd? (lambda (n) > (if (zero? n) #f (even? (- n 1))))) > (even? 1000))) >
No difference at all. Those generate identical code. I believe the second form is transformed into the first during compilation. scheme@(guile-user)> ,x a Disassembly of #<procedure a ()>: 0 (assert-nargs-ee/locals 8) 2 (br :L204) ;; -> 25 at (unknown file):15:9 6 (local-ref 0) ;; `n' 8 (make-int8:0) ;; 0 at (unknown file):16:8 9 (ee?) 10 (br-if-not :L205) ;; -> 16 at (unknown file):16:4 14 (make-true) ;; #t 15 (return) 16 (local-ref 0) ;; `n' 18 (sub1) at (unknown file):16:27 19 (local-set 0) ;; `n' 21 (br :L206) ;; -> 29 at (unknown file):16:21 25 (br :L207) ;; -> 48 at (unknown file):17:8 29 (local-ref 0) ;; `n' 31 (make-int8:0) ;; 0 at (unknown file):18:8 32 (ee?) 33 (br-if-not :L208) ;; -> 39 at (unknown file):18:4 37 (make-false) 38 (return) 39 (local-ref 0) ;; `n' 41 (sub1) at (unknown file):18:28 42 (local-set 0) ;; `n' 44 (br :L209) ;; -> 6 at (unknown file):18:21 48 (make-int16 3 232) ;; 1000 51 (local-set 0) 53 (br :L209) ;; -> 6 at (unknown file):19:2 scheme@(guile-user)> ,x b Disassembly of #<procedure b ()>: 0 (assert-nargs-ee/locals 8) 2 (br :L216) ;; -> 25 at (unknown file):23:16 6 (local-ref 0) ;; `n' 8 (make-int8:0) ;; 0 at (unknown file):24:8 9 (ee?) 10 (br-if-not :L217) ;; -> 16 at (unknown file):24:4 14 (make-true) ;; #t 15 (return) 16 (local-ref 0) ;; `n' 18 (sub1) at (unknown file):24:27 19 (local-set 0) ;; `n' 21 (br :L218) ;; -> 29 at (unknown file):24:21 25 (br :L219) ;; -> 48 at (unknown file):25:15 29 (local-ref 0) ;; `n' 31 (make-int8:0) ;; 0 at (unknown file):26:8 32 (ee?) 33 (br-if-not :L220) ;; -> 39 at (unknown file):26:4 37 (make-false) 38 (return) 39 (local-ref 0) ;; `n' 41 (sub1) at (unknown file):26:28 42 (local-set 0) ;; `n' 44 (br :L221) ;; -> 6 at (unknown file):26:21 48 (make-int16 3 232) ;; 1000 51 (local-set 0) 53 (br :L221) ;; -> 6 at (unknown file):27:2 -Dale
