Merge 81396ae into e873795

Author: countvajhula

qi-lib/flow.rkt

@@ -0,0 +1,46 @@
+#lang racket/base
+
+(provide literal
+         subject
+         clause
+         starts-with)
+
+(require syntax/parse
+         racket/string)
+
+(define-syntax-class literal
+  (pattern
+   (~or* expr:boolean
+         expr:char
+         expr:string
+         expr:bytes
+         expr:number
+         expr:regexp
+         expr:byte-regexp
+         ;; We'd like to treat quoted forms as literals as well. This
+         ;; includes symbols, and would also include, for instance,
+         ;; syntactic specifications of flows, since flows are
+         ;; syntactically lists as they inherit the elementary syntax of
+         ;; the underlying language (Racket). Quoted forms are read as
+         ;; (quote ...), so we match against this
+         ((~datum quote) expr:expr)
+         ((~datum quasiquote) expr:expr)
+         ((~datum quote-syntax) expr:expr)
+         ((~datum syntax) expr:expr))))
+
+(define-syntax-class subject
+  #:attributes (args arity)
+  (pattern
+   (arg:expr ...)
+   #:with args #'(arg ...)
+   #:attr arity (length (syntax->list #'args))))
+
+(define-syntax-class clause
+  (pattern
+   expr:expr))
+
+(define-syntax-class (starts-with pfx)
+  (pattern
+   i:id #:when (string-prefix? (symbol->string
+                                (syntax-e #'i)) pfx)))
+