Add syntax/parse/lib/function-header library.

racket/collects/syntax/parse/lib/function-header.rkt

@@ -0,0 +1,26 @@
+#lang racket/base
+
+(require "../../parse.rkt"
+         "../experimental/template.rkt")
+
+(provide (all-defined-out))
+
+(define-syntax-class function-header
+  (pattern ((~or header:function-header name:id) . args:args)
+           #:attr params
+           (template ((?@ . (?? header.params ()))
+                      . args.params))))
+
+(define-syntax-class args
+  (pattern (arg:arg ...)
+           #:attr params #'(arg.name ...))
+  (pattern (arg:arg ... . rest:id)
+           #:attr params #'(arg.name ... rest)))
+
+(define-splicing-syntax-class arg
+  #:attributes (name)
+  (pattern name:id)
+  (pattern [name:id default])
+  (pattern (~seq kw:keyword name:id))
+  (pattern (~seq kw:keyword [name:id default])))
+