allow arbitrary number of dashes in type rules

closes #23

turnstile/examples/stlc.rkt

@@ -30,11 +30,11 @@
 (define-typed-syntax λ #:datum-literals (:)
   [(λ ([x:id : τ_in:type] ...) e) ≫
    [([x ≫ x- : τ_in.norm] ...) ⊢ [e ≫ e- ⇒ τ_out]]
-   --------
+   -------
    [⊢ [_ ≫ (λ- (x- ...) e-) ⇒ (→ τ_in.norm ... τ_out)]]]
   [(λ (x:id ...) e) ⇐ (~→ τ_in ... τ_out) ≫
    [([x ≫ x- : τ_in] ...) ⊢ [e ≫ e- ⇐ τ_out]]
-   --------
+   ---------
    [⊢ [_ ≫ (λ- (x- ...) e-) ⇐ _]]])
 
 (define-typed-syntax #%app

turnstile/turnstile.rkt

@@ -58,7 +58,13 @@
            (for-meta -1 (submod ".." typecheck+) (except-in macrotypes/typecheck #%module-begin))
            (for-meta -2 (except-in macrotypes/typecheck #%module-begin)))
   (define-syntax-class ---
-    [pattern (~datum --------)])
+    [pattern dashes
+             #:do [(define str-dashes (symbol->string (syntax->datum #'dashes)))]
+             #:fail-unless (for/and ([d (in-string str-dashes)])
+                             (char=? #\- d))
+                           "expected a separator consisting of dashes"
+             #:fail-unless (>= (string-length str-dashes) 3)
+                           "expected a separator of three or more dashes"])
   (define-syntax-class elipsis
     [pattern (~literal ...)])