turnstile is a grammar language created in 2017 by Stephen Chang and Alex Knauth and Ben Greenman and Milo Turner and Michael Ballantyne.
| #2601on PLDB | 7Years Old |
Turnstile aims to help Racket programmers create typed languages. It does so with extensions of Racket’s macro-definition forms that facilitate implementation of type rules alongside normal macro code. As a result, the macros implementing a new language directly type check the program during expansion, obviating the need to create and call out to a separate type checker. Thus, a complete typed language implementation remains a series of macro definitions that may be imported and exported in the standard way that Racket programmers are accustomed to.
#lang turnstile
(provide → Int λ #%app #%datum + ann)
(define-base-type Int)
(define-type-constructor → #:arity > 0)
(define-primop + : (→ Int Int Int))
; [APP]
(define-typed-syntax (#%app e_fn e_arg ...) ≫
[⊢ e_fn ≫ e_fn- ⇒ (~→ τ_in ... τ_out)]
#:fail-unless (stx-length=? #'[τ_in ...] #'[e_arg ...])
(format "arity mismatch, expected ~a args, given ~a"
(stx-length #'[τ_in ...]) #'[e_arg ...])
[⊢ e_arg ≫ e_arg- ⇐ τ_in] ...
--------
[⊢ (#%app- e_fn- e_arg- ...) ⇒ τ_out])
; [LAM]
(define-typed-syntax λ #:datum-literals (:)
[(_ ([x:id : τ_in:type] ...) e) ≫
[[x ≫ x- : τ_in.norm] ... ⊢ e ≫ e- ⇒ τ_out]
-------
[⊢ (λ- (x- ...) e-) ⇒ (→ τ_in.norm ... τ_out)]]
[(_ (x:id ...) e) ⇐ (~→ τ_in ... τ_out) ≫
[[x ≫ x- : τ_in] ... ⊢ e ≫ e- ⇐ τ_out]
---------
[⊢ (λ- (x- ...) e-)]])
; [ANN]
(define-typed-syntax (ann e (~datum :) τ:type) ≫
[⊢ e ≫ e- ⇐ τ.norm]
--------
[⊢ e- ⇒ τ.norm])
; [DATUM]
(define-typed-syntax #%datum
[(_ . n:integer) ≫
--------
[⊢ (#%datum- . n) ⇒ Int]]
[(_ . x) ≫
--------
[#:error (type-error #:src #'x
#:msg "Unsupported literal: ~v" #'x)]])| Feature | Supported | Example | Token |
|---|---|---|---|
| Comments | ✓ | ; A comment | |
| Line Comments | ✓ | ; A comment | ; |
| Semantic Indentation | X |