add stlc-sub with type soundness property

This commit is contained in:
Burke Fetscher 2014-03-21 13:54:36 -05:00
parent bbec642284
commit 51651d2dc4
8 changed files with 1388 additions and 0 deletions

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3c3
< (define the-error "no error")
---
> (define the-error "forgot the variable case")
106,107d105
< [(subst x x M_x)
< M_x]
272,294c270,281
< ;; rewrite all βv redexes already in the term
< ;; (but not any new ones that might appear)
< (define-metafunction stlc
< βv-> : M -> M
< [(βv-> ((λ (x τ) M) v)) (subst (βv-> M) x (βv-> v))]
< [(βv-> ((λ (x τ) M) y)) (subst (βv-> M) x y)]
< [(βv-> (λ (x τ) M)) (λ (x τ) (βv-> M))]
< [(βv-> (M N)) ((βv-> M) (βv-> N))]
< [(βv-> M) M])
<
< ;; check : (or/c #f M) -> boolean[#f = counterexample found!]
< (define (check M)
< (or (not M)
< (let ([M-type (type-check M)])
< (implies M-type
< (let* ([N (term (βv-> ,M))][N-type (type-check N)])
< (and (equal? N-type M-type)
< (let ([a1 (Eval M)] [a2 (Eval N)])
< (and (not (string? a1)) (not (string? a2))
< (equal? a1 a2)
< (or (equal? a1 'error)
< (and (equal? (type-check a1) M-type)
< (equal? (type-check a2) M-type)))))))))))
---
> (define (check term)
> (or (not term)
> (v? term)
> (let ([t-type (type-check term)])
> (implies
> t-type
> (let ([red-res (apply-reduction-relation red term)])
> (and (= (length red-res) 1)
> (let ([red-t (car red-res)])
> (or (equal? red-t "error")
> (let ([red-type (type-check red-t)])
> (equal? t-type red-type))))))))))
298a286,289
> (define small-counter-example
> (term ((λ (x int) x) 1)))
> (test-equal (check small-counter-example) #f)
>

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3c3
< (define the-error "no error")
---
> (define the-error "wrong order of arguments to replace call")
111c111
< (λ (x_new τ) (subst (replace M y x_new) x M_x))
---
> (λ (x_new τ) (subst (replace M x_new y) x M_x))
147a148
>
272,294c273,284
< ;; rewrite all βv redexes already in the term
< ;; (but not any new ones that might appear)
< (define-metafunction stlc
< βv-> : M -> M
< [(βv-> ((λ (x τ) M) v)) (subst (βv-> M) x (βv-> v))]
< [(βv-> ((λ (x τ) M) y)) (subst (βv-> M) x y)]
< [(βv-> (λ (x τ) M)) (λ (x τ) (βv-> M))]
< [(βv-> (M N)) ((βv-> M) (βv-> N))]
< [(βv-> M) M])
<
< ;; check : (or/c #f M) -> boolean[#f = counterexample found!]
< (define (check M)
< (or (not M)
< (let ([M-type (type-check M)])
< (implies M-type
< (let* ([N (term (βv-> ,M))][N-type (type-check N)])
< (and (equal? N-type M-type)
< (let ([a1 (Eval M)] [a2 (Eval N)])
< (and (not (string? a1)) (not (string? a2))
< (equal? a1 a2)
< (or (equal? a1 'error)
< (and (equal? (type-check a1) M-type)
< (equal? (type-check a2) M-type)))))))))))
---
> (define (check term)
> (or (not term)
> (v? term)
> (let ([t-type (type-check term)])
> (implies
> t-type
> (let ([red-res (apply-reduction-relation red term)])
> (and (= (length red-res) 1)
> (let ([red-t (car red-res)])
> (or (equal? red-t "error")
> (let ([red-type (type-check red-t)])
> (equal? t-type red-type))))))))))
298a289,292
> (define small-counter-example
> (term ((λ (x int) (λ (y int) y)) 1)))
> (test-equal (check small-counter-example) #f)
>

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3c3
< (define the-error "no error")
---
> (define the-error "swaps function and argument position in application")
115c115
< ((subst M x M_x) (subst N x M_x))]
---
> ((subst N x M_x) (subst M x M_x))]
272,294c272,283
< ;; rewrite all βv redexes already in the term
< ;; (but not any new ones that might appear)
< (define-metafunction stlc
< βv-> : M -> M
< [(βv-> ((λ (x τ) M) v)) (subst (βv-> M) x (βv-> v))]
< [(βv-> ((λ (x τ) M) y)) (subst (βv-> M) x y)]
< [(βv-> (λ (x τ) M)) (λ (x τ) (βv-> M))]
< [(βv-> (M N)) ((βv-> M) (βv-> N))]
< [(βv-> M) M])
<
< ;; check : (or/c #f M) -> boolean[#f = counterexample found!]
< (define (check M)
< (or (not M)
< (let ([M-type (type-check M)])
< (implies M-type
< (let* ([N (term (βv-> ,M))][N-type (type-check N)])
< (and (equal? N-type M-type)
< (let ([a1 (Eval M)] [a2 (Eval N)])
< (and (not (string? a1)) (not (string? a2))
< (equal? a1 a2)
< (or (equal? a1 'error)
< (and (equal? (type-check a1) M-type)
< (equal? (type-check a2) M-type)))))))))))
---
> (define (check term)
> (or (not term)
> (v? term)
> (let ([t-type (type-check term)])
> (implies
> t-type
> (let ([red-res (apply-reduction-relation red term)])
> (and (= (length red-res) 1)
> (let ([red-t (car red-res)])
> (or (equal? red-t "error")
> (let ([red-type (type-check red-t)])
> (equal? t-type red-type))))))))))
297a287,290
>
> (define small-counter-example
> (term ((λ (x int) (+ 1)) 1)))
> (test-equal (check small-counter-example) #f)

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3c3
< (define the-error "no error")
---
> (define the-error "replace all variables")
106c106
< [(subst x x M_x)
---
> [(subst x y M_x)
272,294c272,283
< ;; rewrite all βv redexes already in the term
< ;; (but not any new ones that might appear)
< (define-metafunction stlc
< βv-> : M -> M
< [(βv-> ((λ (x τ) M) v)) (subst (βv-> M) x (βv-> v))]
< [(βv-> ((λ (x τ) M) y)) (subst (βv-> M) x y)]
< [(βv-> (λ (x τ) M)) (λ (x τ) (βv-> M))]
< [(βv-> (M N)) ((βv-> M) (βv-> N))]
< [(βv-> M) M])
<
< ;; check : (or/c #f M) -> boolean[#f = counterexample found!]
< (define (check M)
< (or (not M)
< (let ([M-type (type-check M)])
< (implies M-type
< (let* ([N (term (βv-> ,M))][N-type (type-check N)])
< (and (equal? N-type M-type)
< (let ([a1 (Eval M)] [a2 (Eval N)])
< (and (not (string? a1)) (not (string? a2))
< (equal? a1 a2)
< (or (equal? a1 'error)
< (and (equal? (type-check a1) M-type)
< (equal? (type-check a2) M-type)))))))))))
---
> (define (check term)
> (or (not term)
> (v? term)
> (let ([t-type (type-check term)])
> (implies
> t-type
> (let ([red-res (apply-reduction-relation red term)])
> (and (= (length red-res) 1)
> (let ([red-t (car red-res)])
> (or (equal? red-t "error")
> (let ([red-type (type-check red-t)])
> (equal? t-type red-type))))))))))
298a288,291
> (define small-counter-example
> (term ((λ (x int) (λ (y (list int)) (hd y))) 1)))
> (test-equal (check small-counter-example) #f)
>

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#lang racket/base
(define the-error "forgot the variable case")
(require redex/reduction-semantics
(only-in redex/private/generate-term pick-an-index)
racket/match
racket/list
racket/contract
racket/bool)
(provide (all-defined-out))
(define-language stlc
(M N ::=
(λ (x σ) M)
(M N)
x
c)
(Γ (x σ Γ)
)
(σ τ ::=
int
(list int)
(σ τ))
(c d ::= cons nil hd tl + integer)
((x y) variable-not-otherwise-mentioned)
(v (λ (x τ) M)
c
(cons v)
((cons v) v)
(+ v))
(E hole
(E M)
(v E)))
(define-judgment-form stlc
#:mode (typeof I I O)
#:contract (typeof Γ M σ)
[---------------------------
(typeof Γ c (const-type c))]
[(where τ (lookup Γ x))
----------------------
(typeof Γ x τ)]
[(typeof (x σ Γ) M σ_2)
--------------------------------
(typeof Γ (λ (x σ) M) (σ σ_2))]
[(typeof Γ M (σ σ_2))
(typeof Γ M_2 σ)
----------------------
(typeof Γ (M M_2) σ_2)])
(define-metafunction stlc
const-type : c -> σ
[(const-type nil)
(list int)]
[(const-type cons)
(int ((list int) (list int)))]
[(const-type hd)
((list int) int)]
[(const-type tl)
((list int) (list int))]
[(const-type +)
(int (int int))]
[(const-type integer)
int])
(define-metafunction stlc
lookup : Γ x -> σ or #f
[(lookup (x σ Γ) x)
σ]
[(lookup (x σ Γ) x_2)
(lookup Γ x_2)]
[(lookup x)
#f])
(define red
(reduction-relation
stlc
(--> (in-hole E ((λ (x τ) M) v))
(in-hole E (subst M x v))
"βv")
(--> (in-hole E (hd ((cons v_1) v_2)))
(in-hole E v_1)
"hd")
(--> (in-hole E (tl ((cons v_1) v_2)))
(in-hole E v_2)
"tl")
(--> (in-hole E (hd nil))
"error"
"hd-err")
(--> (in-hole E (tl nil))
"error"
"tl-err")
(--> (in-hole E ((+ integer_1) integer_2))
(in-hole E ,(+ (term integer_1) (term integer_2)))
"+")))
(define-metafunction stlc
subst : M x M -> M
[(subst (λ (x τ) M) x M_x)
(λ (x τ) M)]
[(subst (λ (y τ) M) x M_x)
(λ (x_new τ) (subst (replace M y x_new) x M_x))
(where x_new ,(variable-not-in (term (x y M))
(term y)))]
[(subst (M N) x M_x)
((subst M x M_x) (subst N x M_x))]
[(subst M x M_z)
M])
(define-metafunction stlc
[(replace (any_1 ...) x_1 x_new)
((replace any_1 x_1 x_new) ...)]
[(replace x_1 x_1 x_new)
x_new]
[(replace any_1 x_1 x_new)
any_1])
(define M? (redex-match stlc M))
(define/contract (Eval M)
(-> M? (or/c M? string? 'error))
(define M-t (judgment-holds (typeof ,M τ) τ))
(cond
[(pair? M-t)
(define res (apply-reduction-relation* red M))
(cond
[(= 1 (length res))
(define ans (car res))
(if (equal? "error" ans)
'error
(let ([ans-t (judgment-holds (typeof ,ans τ) τ)])
(cond
[(equal? M-t ans-t) ans]
[else (format "internal error: type soundness fails for ~s" M)])))]
[else
(format "internal error: not exactly 1 result ~s => ~s" M res)])]
[else
(error 'Eval "argument doesn't typecheck: ~s" M)]))
(define x? (redex-match stlc x))
(define v? (redex-match? stlc v))
(define τ? (redex-match? stlc τ))
(define/contract (type-check M)
(-> M? (or/c τ? #f))
(define M-t (judgment-holds (typeof ,M τ) τ))
(cond
[(empty? M-t)
#f]
[(null? (cdr M-t))
(car M-t)]
[else
(error 'type-check "non-unique type: ~s : ~s" M M-t)]))
(test-equal (type-check (term 5))
(term int))
(test-equal (type-check (term (5 5)))
#f)
(define (progress-holds? M)
(if (type-check M)
(or (v? M)
(not (null? (apply-reduction-relation red (term ,M)))))
#t))
(define (interesting-term? M)
(and (type-check M)
(term (uses-bound-var? () ,M))))
(define-metafunction stlc
[(uses-bound-var? (x_0 ... x_1 x_2 ...) x_1)
#t]
[(uses-bound-var? (x_0 ...) (λ (x τ) M))
(uses-bound-var? (x x_0 ...) M)]
[(uses-bound-var? (x ...) (M N))
,(or (term (uses-bound-var? (x ...) M))
(term (uses-bound-var? (x ...) N)))]
[(uses-bound-var? (x ...) (cons M))
(uses-bound-var? (x ...) M)]
[(uses-bound-var? (x ...) any)
#f])
(define (really-interesting-term? M)
(and (interesting-term? M)
(term (applies-bv? () ,M))))
(define-metafunction stlc
[(applies-bv? (x_0 ... x_1 x_2 ...) (x_1 M))
#t]
[(applies-bv? (x_0 ...) (λ (x τ) M))
(applies-bv? (x x_0 ...) M)]
[(applies-bv? (x ...) (M N))
,(or (term (applies-bv? (x ...) M))
(term (applies-bv? (x ...) N)))]
[(applies-bv? (x ...) (cons M))
(applies-bv? (x ...) M)]
[(applies-bv? (x ...) any)
#f])
(define (reduction-step-count/func red v?)
(λ (term)
(let loop ([t term]
[n 0])
(define res (apply-reduction-relation red t))
(cond
[(and (empty? res)
(v? t))
n]
[(and (empty? res)
(equal? t "error"))
n]
[(= (length res) 1)
(loop (car res) (add1 n))]
[else
(error 'reduction-step-count "failed reduction: ~s\n~s\n~s" term t res)]))))
(define reduction-step-count
(reduction-step-count/func red v?))
(define (generate-M-term)
(generate-term stlc M 5))
(define (generate-M-term-from-red)
(generate-term #:source red 5))
(define (generate-typed-term)
(match (generate-term stlc
#:satisfying
(typeof M τ)
5)
[`(typeof ,M ,τ)
M]
[#f #f]))
(define (generate-typed-term-from-red)
(define candidate
(case (random 5)
[(0)
(generate-term stlc #:satisfying (typeof ((λ (x τ_x) M) v) ((list int) (list int))) 5)]
[(1)
(generate-term stlc #:satisfying (typeof (hd ((cons v_1) v_2)) ((list int) (list int))) 5)]
[(2)
(generate-term stlc #:satisfying (typeof (tl ((cons v_1) v_2)) ((list int) (list int))) 5)]
[(3)
(generate-term stlc #:satisfying (typeof (hd nil) ((list int) (list int))) 5)]
[(4)
(generate-term stlc #:satisfying (typeof (tl nil) ((list int) (list int))) 5)]))
(match candidate
[`(typeof ,M ,τ)
M]
[#f #f]))
(define (typed-generator)
(let ([g (redex-generator stlc
(typeof M τ)
5)])
(λ ()
(match (g)
[`(typeof ,M ,τ)
M]
[#f #f]))))
(define (check term)
(or (not term)
(v? term)
(let ([t-type (type-check term)])
(implies
t-type
(let ([red-res (apply-reduction-relation red term)])
(and (= (length red-res) 1)
(let ([red-t (car red-res)])
(or (equal? red-t "error")
(let ([red-type (type-check red-t)])
(equal? t-type red-type))))))))))
(define (generate-enum-term)
(generate-term stlc M #:i-th (pick-an-index 0.035)))
(define small-counter-example
(term ((λ (x int) x) 1)))
(test-equal (check small-counter-example) #f)
(define (ordered-enum-generator)
(let ([index 0])
(λ ()
(begin0
(generate-term stlc M #:i-th index)
(set! index (add1 index))))))

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#lang racket/base
(define the-error "wrong order of arguments to replace call")
(require redex/reduction-semantics
(only-in redex/private/generate-term pick-an-index)
racket/match
racket/list
racket/contract
racket/bool)
(provide (all-defined-out))
(define-language stlc
(M N ::=
(λ (x σ) M)
(M N)
x
c)
(Γ (x σ Γ)
)
(σ τ ::=
int
(list int)
(σ τ))
(c d ::= cons nil hd tl + integer)
((x y) variable-not-otherwise-mentioned)
(v (λ (x τ) M)
c
(cons v)
((cons v) v)
(+ v))
(E hole
(E M)
(v E)))
(define-judgment-form stlc
#:mode (typeof I I O)
#:contract (typeof Γ M σ)
[---------------------------
(typeof Γ c (const-type c))]
[(where τ (lookup Γ x))
----------------------
(typeof Γ x τ)]
[(typeof (x σ Γ) M σ_2)
--------------------------------
(typeof Γ (λ (x σ) M) (σ σ_2))]
[(typeof Γ M (σ σ_2))
(typeof Γ M_2 σ)
----------------------
(typeof Γ (M M_2) σ_2)])
(define-metafunction stlc
const-type : c -> σ
[(const-type nil)
(list int)]
[(const-type cons)
(int ((list int) (list int)))]
[(const-type hd)
((list int) int)]
[(const-type tl)
((list int) (list int))]
[(const-type +)
(int (int int))]
[(const-type integer)
int])
(define-metafunction stlc
lookup : Γ x -> σ or #f
[(lookup (x σ Γ) x)
σ]
[(lookup (x σ Γ) x_2)
(lookup Γ x_2)]
[(lookup x)
#f])
(define red
(reduction-relation
stlc
(--> (in-hole E ((λ (x τ) M) v))
(in-hole E (subst M x v))
"βv")
(--> (in-hole E (hd ((cons v_1) v_2)))
(in-hole E v_1)
"hd")
(--> (in-hole E (tl ((cons v_1) v_2)))
(in-hole E v_2)
"tl")
(--> (in-hole E (hd nil))
"error"
"hd-err")
(--> (in-hole E (tl nil))
"error"
"tl-err")
(--> (in-hole E ((+ integer_1) integer_2))
(in-hole E ,(+ (term integer_1) (term integer_2)))
"+")))
(define-metafunction stlc
subst : M x M -> M
[(subst x x M_x)
M_x]
[(subst (λ (x τ) M) x M_x)
(λ (x τ) M)]
[(subst (λ (y τ) M) x M_x)
(λ (x_new τ) (subst (replace M x_new y) x M_x))
(where x_new ,(variable-not-in (term (x y M))
(term y)))]
[(subst (M N) x M_x)
((subst M x M_x) (subst N x M_x))]
[(subst M x M_z)
M])
(define-metafunction stlc
[(replace (any_1 ...) x_1 x_new)
((replace any_1 x_1 x_new) ...)]
[(replace x_1 x_1 x_new)
x_new]
[(replace any_1 x_1 x_new)
any_1])
(define M? (redex-match stlc M))
(define/contract (Eval M)
(-> M? (or/c M? string? 'error))
(define M-t (judgment-holds (typeof ,M τ) τ))
(cond
[(pair? M-t)
(define res (apply-reduction-relation* red M))
(cond
[(= 1 (length res))
(define ans (car res))
(if (equal? "error" ans)
'error
(let ([ans-t (judgment-holds (typeof ,ans τ) τ)])
(cond
[(equal? M-t ans-t) ans]
[else (format "internal error: type soundness fails for ~s" M)])))]
[else
(format "internal error: not exactly 1 result ~s => ~s" M res)])]
[else
(error 'Eval "argument doesn't typecheck: ~s" M)]))
(define x? (redex-match stlc x))
(define v? (redex-match? stlc v))
(define τ? (redex-match? stlc τ))
(define/contract (type-check M)
(-> M? (or/c τ? #f))
(define M-t (judgment-holds (typeof ,M τ) τ))
(cond
[(empty? M-t)
#f]
[(null? (cdr M-t))
(car M-t)]
[else
(error 'type-check "non-unique type: ~s : ~s" M M-t)]))
(test-equal (type-check (term 5))
(term int))
(test-equal (type-check (term (5 5)))
#f)
(define (progress-holds? M)
(if (type-check M)
(or (v? M)
(not (null? (apply-reduction-relation red (term ,M)))))
#t))
(define (interesting-term? M)
(and (type-check M)
(term (uses-bound-var? () ,M))))
(define-metafunction stlc
[(uses-bound-var? (x_0 ... x_1 x_2 ...) x_1)
#t]
[(uses-bound-var? (x_0 ...) (λ (x τ) M))
(uses-bound-var? (x x_0 ...) M)]
[(uses-bound-var? (x ...) (M N))
,(or (term (uses-bound-var? (x ...) M))
(term (uses-bound-var? (x ...) N)))]
[(uses-bound-var? (x ...) (cons M))
(uses-bound-var? (x ...) M)]
[(uses-bound-var? (x ...) any)
#f])
(define (really-interesting-term? M)
(and (interesting-term? M)
(term (applies-bv? () ,M))))
(define-metafunction stlc
[(applies-bv? (x_0 ... x_1 x_2 ...) (x_1 M))
#t]
[(applies-bv? (x_0 ...) (λ (x τ) M))
(applies-bv? (x x_0 ...) M)]
[(applies-bv? (x ...) (M N))
,(or (term (applies-bv? (x ...) M))
(term (applies-bv? (x ...) N)))]
[(applies-bv? (x ...) (cons M))
(applies-bv? (x ...) M)]
[(applies-bv? (x ...) any)
#f])
(define (reduction-step-count/func red v?)
(λ (term)
(let loop ([t term]
[n 0])
(define res (apply-reduction-relation red t))
(cond
[(and (empty? res)
(v? t))
n]
[(and (empty? res)
(equal? t "error"))
n]
[(= (length res) 1)
(loop (car res) (add1 n))]
[else
(error 'reduction-step-count "failed reduction: ~s\n~s\n~s" term t res)]))))
(define reduction-step-count
(reduction-step-count/func red v?))
(define (generate-M-term)
(generate-term stlc M 5))
(define (generate-M-term-from-red)
(generate-term #:source red 5))
(define (generate-typed-term)
(match (generate-term stlc
#:satisfying
(typeof M τ)
5)
[`(typeof ,M ,τ)
M]
[#f #f]))
(define (generate-typed-term-from-red)
(define candidate
(case (random 5)
[(0)
(generate-term stlc #:satisfying (typeof ((λ (x τ_x) M) v) ((list int) (list int))) 5)]
[(1)
(generate-term stlc #:satisfying (typeof (hd ((cons v_1) v_2)) ((list int) (list int))) 5)]
[(2)
(generate-term stlc #:satisfying (typeof (tl ((cons v_1) v_2)) ((list int) (list int))) 5)]
[(3)
(generate-term stlc #:satisfying (typeof (hd nil) ((list int) (list int))) 5)]
[(4)
(generate-term stlc #:satisfying (typeof (tl nil) ((list int) (list int))) 5)]))
(match candidate
[`(typeof ,M ,τ)
M]
[#f #f]))
(define (typed-generator)
(let ([g (redex-generator stlc
(typeof M τ)
5)])
(λ ()
(match (g)
[`(typeof ,M ,τ)
M]
[#f #f]))))
(define (check term)
(or (not term)
(v? term)
(let ([t-type (type-check term)])
(implies
t-type
(let ([red-res (apply-reduction-relation red term)])
(and (= (length red-res) 1)
(let ([red-t (car red-res)])
(or (equal? red-t "error")
(let ([red-type (type-check red-t)])
(equal? t-type red-type))))))))))
(define (generate-enum-term)
(generate-term stlc M #:i-th (pick-an-index 0.035)))
(define small-counter-example
(term ((λ (x int) (λ (y int) y)) 1)))
(test-equal (check small-counter-example) #f)
(define (ordered-enum-generator)
(let ([index 0])
(λ ()
(begin0
(generate-term stlc M #:i-th index)
(set! index (add1 index))))))

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#lang racket/base
(define the-error "swaps function and argument position in application")
(require redex/reduction-semantics
(only-in redex/private/generate-term pick-an-index)
racket/match
racket/list
racket/contract
racket/bool)
(provide (all-defined-out))
(define-language stlc
(M N ::=
(λ (x σ) M)
(M N)
x
c)
(Γ (x σ Γ)
)
(σ τ ::=
int
(list int)
(σ τ))
(c d ::= cons nil hd tl + integer)
((x y) variable-not-otherwise-mentioned)
(v (λ (x τ) M)
c
(cons v)
((cons v) v)
(+ v))
(E hole
(E M)
(v E)))
(define-judgment-form stlc
#:mode (typeof I I O)
#:contract (typeof Γ M σ)
[---------------------------
(typeof Γ c (const-type c))]
[(where τ (lookup Γ x))
----------------------
(typeof Γ x τ)]
[(typeof (x σ Γ) M σ_2)
--------------------------------
(typeof Γ (λ (x σ) M) (σ σ_2))]
[(typeof Γ M (σ σ_2))
(typeof Γ M_2 σ)
----------------------
(typeof Γ (M M_2) σ_2)])
(define-metafunction stlc
const-type : c -> σ
[(const-type nil)
(list int)]
[(const-type cons)
(int ((list int) (list int)))]
[(const-type hd)
((list int) int)]
[(const-type tl)
((list int) (list int))]
[(const-type +)
(int (int int))]
[(const-type integer)
int])
(define-metafunction stlc
lookup : Γ x -> σ or #f
[(lookup (x σ Γ) x)
σ]
[(lookup (x σ Γ) x_2)
(lookup Γ x_2)]
[(lookup x)
#f])
(define red
(reduction-relation
stlc
(--> (in-hole E ((λ (x τ) M) v))
(in-hole E (subst M x v))
"βv")
(--> (in-hole E (hd ((cons v_1) v_2)))
(in-hole E v_1)
"hd")
(--> (in-hole E (tl ((cons v_1) v_2)))
(in-hole E v_2)
"tl")
(--> (in-hole E (hd nil))
"error"
"hd-err")
(--> (in-hole E (tl nil))
"error"
"tl-err")
(--> (in-hole E ((+ integer_1) integer_2))
(in-hole E ,(+ (term integer_1) (term integer_2)))
"+")))
(define-metafunction stlc
subst : M x M -> M
[(subst x x M_x)
M_x]
[(subst (λ (x τ) M) x M_x)
(λ (x τ) M)]
[(subst (λ (y τ) M) x M_x)
(λ (x_new τ) (subst (replace M y x_new) x M_x))
(where x_new ,(variable-not-in (term (x y M))
(term y)))]
[(subst (M N) x M_x)
((subst N x M_x) (subst M x M_x))]
[(subst M x M_z)
M])
(define-metafunction stlc
[(replace (any_1 ...) x_1 x_new)
((replace any_1 x_1 x_new) ...)]
[(replace x_1 x_1 x_new)
x_new]
[(replace any_1 x_1 x_new)
any_1])
(define M? (redex-match stlc M))
(define/contract (Eval M)
(-> M? (or/c M? string? 'error))
(define M-t (judgment-holds (typeof ,M τ) τ))
(cond
[(pair? M-t)
(define res (apply-reduction-relation* red M))
(cond
[(= 1 (length res))
(define ans (car res))
(if (equal? "error" ans)
'error
(let ([ans-t (judgment-holds (typeof ,ans τ) τ)])
(cond
[(equal? M-t ans-t) ans]
[else (format "internal error: type soundness fails for ~s" M)])))]
[else
(format "internal error: not exactly 1 result ~s => ~s" M res)])]
[else
(error 'Eval "argument doesn't typecheck: ~s" M)]))
(define x? (redex-match stlc x))
(define v? (redex-match? stlc v))
(define τ? (redex-match? stlc τ))
(define/contract (type-check M)
(-> M? (or/c τ? #f))
(define M-t (judgment-holds (typeof ,M τ) τ))
(cond
[(empty? M-t)
#f]
[(null? (cdr M-t))
(car M-t)]
[else
(error 'type-check "non-unique type: ~s : ~s" M M-t)]))
(test-equal (type-check (term 5))
(term int))
(test-equal (type-check (term (5 5)))
#f)
(define (progress-holds? M)
(if (type-check M)
(or (v? M)
(not (null? (apply-reduction-relation red (term ,M)))))
#t))
(define (interesting-term? M)
(and (type-check M)
(term (uses-bound-var? () ,M))))
(define-metafunction stlc
[(uses-bound-var? (x_0 ... x_1 x_2 ...) x_1)
#t]
[(uses-bound-var? (x_0 ...) (λ (x τ) M))
(uses-bound-var? (x x_0 ...) M)]
[(uses-bound-var? (x ...) (M N))
,(or (term (uses-bound-var? (x ...) M))
(term (uses-bound-var? (x ...) N)))]
[(uses-bound-var? (x ...) (cons M))
(uses-bound-var? (x ...) M)]
[(uses-bound-var? (x ...) any)
#f])
(define (really-interesting-term? M)
(and (interesting-term? M)
(term (applies-bv? () ,M))))
(define-metafunction stlc
[(applies-bv? (x_0 ... x_1 x_2 ...) (x_1 M))
#t]
[(applies-bv? (x_0 ...) (λ (x τ) M))
(applies-bv? (x x_0 ...) M)]
[(applies-bv? (x ...) (M N))
,(or (term (applies-bv? (x ...) M))
(term (applies-bv? (x ...) N)))]
[(applies-bv? (x ...) (cons M))
(applies-bv? (x ...) M)]
[(applies-bv? (x ...) any)
#f])
(define (reduction-step-count/func red v?)
(λ (term)
(let loop ([t term]
[n 0])
(define res (apply-reduction-relation red t))
(cond
[(and (empty? res)
(v? t))
n]
[(and (empty? res)
(equal? t "error"))
n]
[(= (length res) 1)
(loop (car res) (add1 n))]
[else
(error 'reduction-step-count "failed reduction: ~s\n~s\n~s" term t res)]))))
(define reduction-step-count
(reduction-step-count/func red v?))
(define (generate-M-term)
(generate-term stlc M 5))
(define (generate-M-term-from-red)
(generate-term #:source red 5))
(define (generate-typed-term)
(match (generate-term stlc
#:satisfying
(typeof M τ)
5)
[`(typeof ,M ,τ)
M]
[#f #f]))
(define (generate-typed-term-from-red)
(define candidate
(case (random 5)
[(0)
(generate-term stlc #:satisfying (typeof ((λ (x τ_x) M) v) ((list int) (list int))) 5)]
[(1)
(generate-term stlc #:satisfying (typeof (hd ((cons v_1) v_2)) ((list int) (list int))) 5)]
[(2)
(generate-term stlc #:satisfying (typeof (tl ((cons v_1) v_2)) ((list int) (list int))) 5)]
[(3)
(generate-term stlc #:satisfying (typeof (hd nil) ((list int) (list int))) 5)]
[(4)
(generate-term stlc #:satisfying (typeof (tl nil) ((list int) (list int))) 5)]))
(match candidate
[`(typeof ,M ,τ)
M]
[#f #f]))
(define (typed-generator)
(let ([g (redex-generator stlc
(typeof M τ)
5)])
(λ ()
(match (g)
[`(typeof ,M ,τ)
M]
[#f #f]))))
(define (check term)
(or (not term)
(v? term)
(let ([t-type (type-check term)])
(implies
t-type
(let ([red-res (apply-reduction-relation red term)])
(and (= (length red-res) 1)
(let ([red-t (car red-res)])
(or (equal? red-t "error")
(let ([red-type (type-check red-t)])
(equal? t-type red-type))))))))))
(define (generate-enum-term)
(generate-term stlc M #:i-th (pick-an-index 0.035)))
(define small-counter-example
(term ((λ (x int) (+ 1)) 1)))
(test-equal (check small-counter-example) #f)
(define (ordered-enum-generator)
(let ([index 0])
(λ ()
(begin0
(generate-term stlc M #:i-th index)
(set! index (add1 index))))))

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#lang racket/base
(define the-error "replace all variables")
(require redex/reduction-semantics
(only-in redex/private/generate-term pick-an-index)
racket/match
racket/list
racket/contract
racket/bool)
(provide (all-defined-out))
(define-language stlc
(M N ::=
(λ (x σ) M)
(M N)
x
c)
(Γ (x σ Γ)
)
(σ τ ::=
int
(list int)
(σ τ))
(c d ::= cons nil hd tl + integer)
((x y) variable-not-otherwise-mentioned)
(v (λ (x τ) M)
c
(cons v)
((cons v) v)
(+ v))
(E hole
(E M)
(v E)))
(define-judgment-form stlc
#:mode (typeof I I O)
#:contract (typeof Γ M σ)
[---------------------------
(typeof Γ c (const-type c))]
[(where τ (lookup Γ x))
----------------------
(typeof Γ x τ)]
[(typeof (x σ Γ) M σ_2)
--------------------------------
(typeof Γ (λ (x σ) M) (σ σ_2))]
[(typeof Γ M (σ σ_2))
(typeof Γ M_2 σ)
----------------------
(typeof Γ (M M_2) σ_2)])
(define-metafunction stlc
const-type : c -> σ
[(const-type nil)
(list int)]
[(const-type cons)
(int ((list int) (list int)))]
[(const-type hd)
((list int) int)]
[(const-type tl)
((list int) (list int))]
[(const-type +)
(int (int int))]
[(const-type integer)
int])
(define-metafunction stlc
lookup : Γ x -> σ or #f
[(lookup (x σ Γ) x)
σ]
[(lookup (x σ Γ) x_2)
(lookup Γ x_2)]
[(lookup x)
#f])
(define red
(reduction-relation
stlc
(--> (in-hole E ((λ (x τ) M) v))
(in-hole E (subst M x v))
"βv")
(--> (in-hole E (hd ((cons v_1) v_2)))
(in-hole E v_1)
"hd")
(--> (in-hole E (tl ((cons v_1) v_2)))
(in-hole E v_2)
"tl")
(--> (in-hole E (hd nil))
"error"
"hd-err")
(--> (in-hole E (tl nil))
"error"
"tl-err")
(--> (in-hole E ((+ integer_1) integer_2))
(in-hole E ,(+ (term integer_1) (term integer_2)))
"+")))
(define-metafunction stlc
subst : M x M -> M
[(subst x y M_x)
M_x]
[(subst (λ (x τ) M) x M_x)
(λ (x τ) M)]
[(subst (λ (y τ) M) x M_x)
(λ (x_new τ) (subst (replace M y x_new) x M_x))
(where x_new ,(variable-not-in (term (x y M))
(term y)))]
[(subst (M N) x M_x)
((subst M x M_x) (subst N x M_x))]
[(subst M x M_z)
M])
(define-metafunction stlc
[(replace (any_1 ...) x_1 x_new)
((replace any_1 x_1 x_new) ...)]
[(replace x_1 x_1 x_new)
x_new]
[(replace any_1 x_1 x_new)
any_1])
(define M? (redex-match stlc M))
(define/contract (Eval M)
(-> M? (or/c M? string? 'error))
(define M-t (judgment-holds (typeof ,M τ) τ))
(cond
[(pair? M-t)
(define res (apply-reduction-relation* red M))
(cond
[(= 1 (length res))
(define ans (car res))
(if (equal? "error" ans)
'error
(let ([ans-t (judgment-holds (typeof ,ans τ) τ)])
(cond
[(equal? M-t ans-t) ans]
[else (format "internal error: type soundness fails for ~s" M)])))]
[else
(format "internal error: not exactly 1 result ~s => ~s" M res)])]
[else
(error 'Eval "argument doesn't typecheck: ~s" M)]))
(define x? (redex-match stlc x))
(define v? (redex-match? stlc v))
(define τ? (redex-match? stlc τ))
(define/contract (type-check M)
(-> M? (or/c τ? #f))
(define M-t (judgment-holds (typeof ,M τ) τ))
(cond
[(empty? M-t)
#f]
[(null? (cdr M-t))
(car M-t)]
[else
(error 'type-check "non-unique type: ~s : ~s" M M-t)]))
(test-equal (type-check (term 5))
(term int))
(test-equal (type-check (term (5 5)))
#f)
(define (progress-holds? M)
(if (type-check M)
(or (v? M)
(not (null? (apply-reduction-relation red (term ,M)))))
#t))
(define (interesting-term? M)
(and (type-check M)
(term (uses-bound-var? () ,M))))
(define-metafunction stlc
[(uses-bound-var? (x_0 ... x_1 x_2 ...) x_1)
#t]
[(uses-bound-var? (x_0 ...) (λ (x τ) M))
(uses-bound-var? (x x_0 ...) M)]
[(uses-bound-var? (x ...) (M N))
,(or (term (uses-bound-var? (x ...) M))
(term (uses-bound-var? (x ...) N)))]
[(uses-bound-var? (x ...) (cons M))
(uses-bound-var? (x ...) M)]
[(uses-bound-var? (x ...) any)
#f])
(define (really-interesting-term? M)
(and (interesting-term? M)
(term (applies-bv? () ,M))))
(define-metafunction stlc
[(applies-bv? (x_0 ... x_1 x_2 ...) (x_1 M))
#t]
[(applies-bv? (x_0 ...) (λ (x τ) M))
(applies-bv? (x x_0 ...) M)]
[(applies-bv? (x ...) (M N))
,(or (term (applies-bv? (x ...) M))
(term (applies-bv? (x ...) N)))]
[(applies-bv? (x ...) (cons M))
(applies-bv? (x ...) M)]
[(applies-bv? (x ...) any)
#f])
(define (reduction-step-count/func red v?)
(λ (term)
(let loop ([t term]
[n 0])
(define res (apply-reduction-relation red t))
(cond
[(and (empty? res)
(v? t))
n]
[(and (empty? res)
(equal? t "error"))
n]
[(= (length res) 1)
(loop (car res) (add1 n))]
[else
(error 'reduction-step-count "failed reduction: ~s\n~s\n~s" term t res)]))))
(define reduction-step-count
(reduction-step-count/func red v?))
(define (generate-M-term)
(generate-term stlc M 5))
(define (generate-M-term-from-red)
(generate-term #:source red 5))
(define (generate-typed-term)
(match (generate-term stlc
#:satisfying
(typeof M τ)
5)
[`(typeof ,M ,τ)
M]
[#f #f]))
(define (generate-typed-term-from-red)
(define candidate
(case (random 5)
[(0)
(generate-term stlc #:satisfying (typeof ((λ (x τ_x) M) v) ((list int) (list int))) 5)]
[(1)
(generate-term stlc #:satisfying (typeof (hd ((cons v_1) v_2)) ((list int) (list int))) 5)]
[(2)
(generate-term stlc #:satisfying (typeof (tl ((cons v_1) v_2)) ((list int) (list int))) 5)]
[(3)
(generate-term stlc #:satisfying (typeof (hd nil) ((list int) (list int))) 5)]
[(4)
(generate-term stlc #:satisfying (typeof (tl nil) ((list int) (list int))) 5)]))
(match candidate
[`(typeof ,M ,τ)
M]
[#f #f]))
(define (typed-generator)
(let ([g (redex-generator stlc
(typeof M τ)
5)])
(λ ()
(match (g)
[`(typeof ,M ,τ)
M]
[#f #f]))))
(define (check term)
(or (not term)
(v? term)
(let ([t-type (type-check term)])
(implies
t-type
(let ([red-res (apply-reduction-relation red term)])
(and (= (length red-res) 1)
(let ([red-t (car red-res)])
(or (equal? red-t "error")
(let ([red-type (type-check red-t)])
(equal? t-type red-type))))))))))
(define (generate-enum-term)
(generate-term stlc M #:i-th (pick-an-index 0.035)))
(define small-counter-example
(term ((λ (x int) (λ (y (list int)) (hd y))) 1)))
(test-equal (check small-counter-example) #f)
(define (ordered-enum-generator)
(let ([index 0])
(λ ()
(begin0
(generate-term stlc M #:i-th index)
(set! index (add1 index))))))