From ad19de6be6b9a9d620d94e3f162dcee1bfda2cf7 Mon Sep 17 00:00:00 2001 From: JJ Date: Wed, 23 Oct 2024 18:10:03 -0700 Subject: restructure code, put implementations into broadly categorical folders --- stlc-hor.rkt | 154 ----------------------------------------------------------- 1 file changed, 154 deletions(-) delete mode 100644 stlc-hor.rkt (limited to 'stlc-hor.rkt') diff --git a/stlc-hor.rkt b/stlc-hor.rkt deleted file mode 100644 index ad568c9..0000000 --- a/stlc-hor.rkt +++ /dev/null @@ -1,154 +0,0 @@ -#lang racket -(require "lib.rkt") -(require "base.rkt") -(provide (all-defined-out)) - -;; The Simply-Typed Lambda Calculus with higher-order references - -;; Whether the system is *predicative* or *impredicative*. -;; The predicative system disallows quantification over references. -;; The impredicative system allows so by tweaking level rules. -(define impredicative? #f) - -;; Checks an expression for syntactic well-formedness. -(define (stlc-hor/expr? expr) - (match expr - [x #:when (symbol? x) #t] - [n #:when (natural? n) #t] - [(or `(new ,e) `(! ,e)) (stlc-hor/expr? e)] - [(or `(set ,e1 ,e2) `(,e1 ,e2)) (and (stlc-hor/expr? e1) (stlc-hor/expr? e2))] - [`(λ (,x : ,t) ,e) (and (symbol? x) (stlc-hor/type? t) (stlc-hor/expr? e))] - [_ #f])) - -;; Checks a type for syntactic well-formedness. -(define (stlc-hor/type? type) - (match type - [t #:when (symbol? t) #t] - [`(,t1 → ,k ,t2) (and (natural? k) (stlc-hor/type? t1) (stlc-hor/type? t2))] - [_ #f])) - -;; Checks a value for syntactic well-formedness. -(define (stlc-hor/value? value) - (match value - [x #:when (symbol? x) #t] - [n #:when (natural? n) #t] - [`(,v1 ,v2) (and (stlc-hor/value? v1) (stlc-hor/value? v2))] - [`(λ ,x ,e ,env) (and (symbol? x) (stlc-hor/expr? e) (dict? env))] - [_ #f])) - -;; Interprets an expression down to a value, in a given context. -(define (interpret expr) - (interpret/core (desugar expr) #hash() (make-hash))) -(define/contract (interpret/core expr Γ Σ) - (-> stlc-hor/expr? dict? dict? stlc-hor/value?) - (match expr - [r #:when (dict-has-key? Σ r) r] - [x #:when (dict-has-key? Γ x) (dict-ref Γ x)] - [f #:when (symbol? f) f] - - [`(new ,e) - (let ([r (gensym)]) - (dict-set! Σ r e) r)] - [`(! ,e) - (let ([r (interpret/core e Γ Σ)]) - (if (dict-has-key? Σ r) - (interpret/core (dict-ref Σ r) Γ Σ) - (err (format "attempting to deref unknown reference ~a" r))))] - [`(set ,e1 ,e2) - (let ([r (interpret/core e1 Γ Σ)]) - (if (dict-has-key? Σ r) (dict-set! Σ r (interpret/core e2 Γ Σ)) - (err (format "attempting to update unknown reference ~a" r)))) - 'sole] - - [`(λ ,x ,e) `(λ ,x ,e ,Γ)] - [`(,e1 ,e2) - (match (interpret/core e1 Γ Σ) - [`(λ ,x ,e1 ,env) - (interpret/core e1 (dict-set env x (interpret/core e2 Γ Σ)) Σ)] - [e1 (err (format "attempting to interpret arg ~a applied to unknown expression ~a" e2 e1))])])) - -;; Checks an expression against some type, in a given context. -(define (check expr with) - (check/core (desugar expr) with #hash())) -(define/contract (check/core expr with Γ) - (-> stlc-hor/expr? stlc-hor/type? dict? boolean?) - (match expr - [`(new ,e) - (match with - [`(Ref ,t) (check/core e t Γ)] - [_ #f])] - [`(! ,e) - (check/core e `(Ref ,with) Γ)] - - [`(λ (,x : ,t) ,e) - (match with - [`(,t1 → ,k ,t2) - (and (equal? t t1) (check/core e t2 (dict-set Γ x t)) - (if impredicative? - (> k (level-expr e (dict-set Γ x t1))) - (>= k (level-expr e (dict-set Γ x t1)))))] - [_ #f])] - - [_ (equal? (infer/core expr Γ) with)])) - -;; Infers a type from some expression, in a given context. -(define (infer expr) - (infer/core (desugar expr) #hash())) -(define/contract (infer/core expr Γ) - (-> stlc-hor/expr? dict? stlc-hor/type?) - (match expr - ['sole 'Unit] - [n #:when (natural? n) 'Nat] - [x #:when (dict-has-key? Γ x) (dict-ref Γ x)] - [f #:when (symbol? f) - (err (format "attempting to infer type of free variable ~a" f))] - - [`(new ,e) `(Ref ,(infer/core e Γ))] - [`(! ,e) - (match (infer/core e Γ) - [`(Ref ,t) t] - [t (err "attempting to deref term not of Ref type!")])] - [`(set ,e1 ,e2) - (match (infer/core e1 Γ) - [`(Ref ,t) - (if (check/core e2 t Γ) 'Unit - (err (format "attempting to update ~a: ~a with term ~a: ~a of differing type" - e1 t e2 (infer/core e2 Γ))))] - [t (err (format "attempting to update non-reference ~a: ~a" e1 t))])] - - [`(λ (,x : ,t1) ,e) - (let ([t2 (infer/core e (dict-set Γ x t1))] - [k (level-expr e (dict-set Γ x t1))]) - `(,t1 → ,(if impredicative? (+ k 1) k) ,t2))] - [`(,e1 ,e2) - (match (infer/core e1 Γ) - [`(,t1 → ,k ,t2) - (if (check/core e2 t1 Γ) t2 - (err (format "inferred argument type ~a does not match arg ~a of type ~a" - t1 e2 (infer/core e2 Γ))))] - [t (err (format "expected → type on application body, got ~a" t))])])) - -;; Get the level associated with a type. This is known at compile time. -(define/contract (level-type type) - (-> stlc-hor/type? natural?) - (match type - [(or 'Unit 'Nat) 0] - [`(Ref ,t) - (let ([k (level-type t)]) - (if (and impredicative? (zero? k)) 0 (+ 1 k)))] - [`(,t1 → ,k ,t2) - (if (and (>= k (level-type t1)) (>= k (level-type t2))) k - (err (format "annotated level ~a is less than inferred levels of ~a and ~a!" - k t1 t2)))] - [t (err (format "attempting to infer the level of unknown type ~a" t))])) - -;; Get the level of an arbitrary expression. This is not known until runtime. -(define/contract (level-expr expr Γ) - (-> stlc-hor/expr? dict? natural?) - (match expr - ['sole 0] - [n #:when (natural? n) 0] - [x #:when (dict-has-key? Γ x) (level-type (dict-ref Γ x))] - [(or `(new ,e) `(! ,e) `(λ (,_ : ,_) ,e)) (level-expr e Γ)] - [(or `(set ,e1 ,e2) `(,e1 ,e2)) (max (level-expr e1 Γ) (level-expr e2 Γ))] - [x #:when (symbol? x) 0])) ; local variables, not in Γ -- cgit v1.2.3-70-g09d2