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add let to stlc

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This commit is contained in:
Stephen Chang 2014-08-05 14:21:47 -04:00
parent b41361a514
commit 063c8fbbb8
2 changed files with 37 additions and 47 deletions
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7
stlc-tests.rkt
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@ -13,4 +13,9 @@
;; shadowed var
(check-type-error ((λ ([x : Int]) ((λ ([x : String]) x) x)) 10))
(check-type-and-result ((λ ([x : String]) ((λ ([x : Int]) (+ x 1)) 10)) "ten") : Int => 11)
(check-type-and-result ((λ ([x : String]) ((λ ([x : Int]) (+ x 1)) 10)) "ten") : Int => 11)
;; let
(check-type-and-result (let ([x 1] [y 2]) (+ x y)) : Int => 3)
(check-type-error (let ([x 1] [y "two"]) (+ x y)))
(check-type-and-result (let ([x "one"]) (let ([x 2]) (+ x x))) : Int => 4)

77
stlc.rkt
View File

@ -5,7 +5,7 @@
(for-meta 2 racket/base syntax/parse))
(provide (except-out (all-from-out racket) λ #%app + #%datum let))
(provide (rename-out [myλ λ] [myapp #%app] [my+ +] [mydatum #%datum] #;[mylet let]))
(provide (rename-out [myλ λ] [myapp #%app] [my+ +] [mydatum #%datum] [mylet let]))
(provide Int String Bool → Listof)
(define Int #f)
@ -14,8 +14,16 @@
(define → #f)
(define Listof #f)
;(define-for-syntax TYPE-ENV-PROP 'Γ)
(define-for-syntax Γ (make-parameter (hash)))
;; type environment
(begin-for-syntax
(define base-type-env (hash))
;; Γ : [Hashof var-symbol => type-stx]
;; - can't use free-identifier=? for the hash table (or free-id-table)
;; because env must be set before expanding λ body (ie before going under λ)
;; so x's in the body won't be free-id=? to the one in the table
;; use symbols instead of identifiers for now --- should be fine because
;; I'm manually managing the environment
(define Γ (make-parameter base-type-env)))
;; testing fns ----------------------------------------------------------------
(require (for-syntax rackunit))
@ -64,20 +72,13 @@
;; retrieves type of τ (from syntax property)
(define-for-syntax (typeof stx) (syntax-property stx 'type))
;; do a local-expand of e, propagating type env (ie Γ) info
;; e is a subexpression in outer-e
#;(define-for-syntax (expand/Γ e outer-e)
(define Γ (syntax-property outer-e 'Γ))
(if (identifier? e)
(syntax-property e 'type (hash-ref Γ (syntax->datum e)))
(local-expand (syntax-property e 'Γ Γ) 'expression null)))
(define-for-syntax (type-env-lookup x) (hash-ref (Γ) (syntax->datum x)))
;; returns a new hash table extended with with tpe associations x:τs
;; returns a new hash table extended with type associations x:τs
(define-for-syntax (type-env-extend x:τs)
(define xs (stx-map stx-car x:τs))
(define τs (stx-map stx-cadr x:τs))
(apply hash-set* (Γ) (append-map (λ (x τ) (list (syntax->datum x) τ)) xs τs)))
;; must be macro because type env must be extended first, before expandinb body
(begin-for-syntax
(define-syntax (with-extended-type-env stx)
(syntax-parse stx
@ -87,27 +88,9 @@
;; depth-first expand
(define-for-syntax (expand/df e)
(if (identifier? e)
(⊢ e (type-env-lookup e))
(⊢ e (type-env-lookup e)) ; handle this here bc there's no #%var form
(local-expand e 'expression null)))
;; do a local-expand of e, a subexpression in outer-e
;; x is bound in e and has type τ and Γ is updated accordingly
;; returns a lambda whose body is e expanded
#;(define-for-syntax (expand/Γ/:= e outer-e x τ)
(define Γ (or (syntax-property outer-e 'Γ) (hash)))
(local-expand
#`(λ (#,x) #,(syntax-property e 'Γ (hash-set Γ (syntax->datum x) τ)))
'expression null))
#;(define-for-syntax (expand/Γ/:=s e outer-e x:τs)
(define Γ (or (syntax-property outer-e TYPE-ENV-PROP) (hash)))
(define xs (stx-map stx-car x:τs))
(define τs (stx-map stx-cadr x:τs))
(local-expand
#`(λ #,xs #,(syntax-property e TYPE-ENV-PROP
(apply hash-set* Γ
(append-map (λ (x τ) (list (syntax->datum x) τ)) xs τs))))
'expression null))
(define-syntax (mydatum stx)
(syntax-parse stx
[(_ . x:integer) (⊢ (syntax/loc stx (#%datum . x)) #'Int)]
@ -120,36 +103,38 @@
(define-syntax (my+ stx)
(syntax-parse stx
[(_ e ...)
; #:with (e+ ...) (stx-map (λ (estx) (expand/Γ estx stx)) #'(e ...))
#:with (e+ ...) (stx-map expand/df #'(e ...))
#:when (andmap (λ (e) (assert-type e #'Int)) (syntax->list #'(e+ ...)))
#:when (stx-andmap (λ (e) (assert-type e #'Int)) #'(e+ ...))
(⊢ (syntax/loc stx (+ e+ ...)) #'Int)]))
(define-syntax (myλ stx)
(syntax-parse stx #:datum-literals (:)
[(_ ([x:id : τ] ...) e)
;; - can't use free-identifier=? for the hash table (or free-id-table)
;; because I have to set the table now, but once I get under the λ, the
;; x's won't be free-id=? to the one in the table
;; use symbols instead of identifiers for now --- should be fine because
;; I'm manually managing the environment
; #:with (lam xs e+) (expand/Γ/:=s #'e stx #'((x τ) ...))
;; the with-extended-type-env must be outside the expand/df (instead of
;; around just the body) bc ow the parameter will get restored to the old
;; value before the local-expand happens
#:with (lam xs e+) (with-extended-type-env #'([x τ] ...)
(expand/df #'(λ (x ...) e)))
#:with τ2 (typeof #'e+)
(⊢ (syntax/loc stx (lam xs e+)) #'(→ τ ... τ2))]))
#:with τ_body (typeof #'e+)
(⊢ (syntax/loc stx (lam xs e+)) #'(→ τ ... τ_body))]))
;(define-syntax (mylet stx)
; (syntax-parse stx #:datum-literals (:)
; [(_ ([x:id : τ e_x] ...) e)
; #:
(define-syntax (mylet stx)
(syntax-parse stx #:datum-literals (:)
[(_ ([x:id e_x] ...) e)
#:with (e_x+ ...) (stx-map expand/df #'(e_x ...))
#:with (τ ...) (stx-map typeof #'(e_x+ ...))
#:with (lam (x+ ...) e+) (with-extended-type-env #'([x τ] ...)
(expand/df #'(λ (x ...) e)))
#:with τ_body (typeof #'e+)
(⊢ (syntax/loc stx (let ([x+ e_x+] ...) e+)) #'τ_body)]))
(define-syntax (myapp stx)
(syntax-parse stx #:literals (→)
[(_ e_fn e_arg ...)
#:with (e_fn+ e_arg+ ...) (stx-map expand/df #'(e_fn e_arg ...))
#:with (→ τ ... τ_res) (typeof #'e_fn+)
; #:when (andmap assert-type (syntax->list #'(e_arg+ ...)) (syntax->list #'(τ ...)))
#:when (stx-andmap assert-type #'(e_arg+ ...) #'(τ ...))
(⊢ (syntax/loc stx (#%app e_fn+ e_arg+ ...)) #'τ_res)]))