Created
August 5, 2011 22:28
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Small-step SOS with define-judgment-form
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#lang racket | |
(require redex) | |
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; ;;;; ;;; ; ; ; ; ; ;; ; ;;; ; ; | |
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(define-language STLC | |
(e (e e) | |
x | |
v) | |
(v (λ (x) e) | |
integer | |
add1) | |
(x variable-not-otherwise-mentioned)) | |
(define-judgment-form STLC | |
mode : I O | |
small-step ⊆ e × e | |
[(small-step ((λ (x) e) v) (subst e x v))] | |
[(small-step (add1 integer) (δ add1 integer))] | |
[(small-step (e_1 e_2) (e_1′ e_2)) | |
(small-step e_1 e_1′)] | |
[(small-step (v e_2) (v e_2′)) | |
(small-step e_2 e_2′)]) | |
(define-judgment-form STLC | |
mode : I O | |
small-step* ⊆ e × e | |
[(small-step* e e)] | |
[(small-step* e_1 e_3) | |
(small-step e_1 e_2) | |
(small-step* e_2 e_3)]) | |
(define-judgment-form STLC | |
mode : I O | |
eval ⊆ e × e | |
[(eval e v) | |
(small-step* e v)]) | |
(define-metafunction STLC | |
[(δ add1 integer) ,(add1 (term integer))]) | |
(define-metafunction STLC | |
subst : e x v -> e | |
[(subst (e_1 e_2) x v) | |
((subst e_1 x v) (subst e_2 x v))] | |
[(subst x x v) v] | |
[(subst x_1 x_2 v) x_1] | |
[(subst (λ (x) e) x v) | |
(λ (x) e)] | |
[(subst (λ (x_1) e) x_2 v) | |
; capture shmapture... | |
(λ (x_1) (subst e x_2 v))] | |
[(subst integer x v) integer] | |
[(subst add1 x v) add1]) | |
(test-equal (judgment-holds (eval (add1 (add1 (add1 0))) v) v) | |
(list (term 3))) | |
(test-equal (judgment-holds | |
(eval (((λ (x) (λ (x) (x (add1 7)))) 0) add1) | |
v) | |
v) | |
(list (term 9))) | |
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; ; ; ; ;;;; ;;; ;;; ;;; ;;; ;;; ; ;;;; ;;;; | |
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; ; ; ; ; ; ;;;;; ;;; ;;;;; ; ; ; ; ; ; ; | |
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; ; ;;;; ;;;; ;;; ;;; ;;; ;; ;; ; ; ; ;;;; | |
; ; ; ; | |
; ; ; ; ; ; | |
; ;;; ;;; | |
(define (rewrite-subst lws) | |
(list "" (list-ref lws 2) "{" (list-ref lws 3) ":=" (list-ref lws 4) "}")) | |
(define (rewrite-small-step lws) | |
(list "" (list-ref lws 2) " → " (list-ref lws 3))) | |
(with-compound-rewriter | |
'small-step rewrite-small-step | |
(with-compound-rewriter | |
'subst rewrite-subst | |
(with-atomic-rewriter | |
'integer "Z" | |
(render-judgment-form small-step)))) | |
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; ; ; ;; ; ;;; ; ; ; ;;;; | |
; ; | |
; ; ; | |
; ;;; | |
(define small-step-rr | |
(reduction-relation | |
STLC | |
(--> e_1 e_2 | |
(judgment-holds (small-step e_1 e_2))))) | |
(traces small-step-rr (term ((λ (x) (add1 x)) 0))) |
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