Reader macro facility - proof of concept

gistfile1.scm

;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Simple PEG Lisp grammar:
;;;;;;;;;;

(syntax (Expression <- (/ Atom List)))

(syntax (Atom <- (/ Number Symbol)))

(syntax (Number <- "[0-9]+")
  `(,(car Number)
    (,(string->number (caadr Number)))))

(syntax (Symbol <- "[a-zA-Z0-9_]+")
  `(,(car Symbol)
    (,(string->symbol (caadr Symbol)))))

(syntax (List <- (: "\\(") (* Expression) (: "\\)"))
  `(,(car List)
    ,(cdr List)))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Let's extend it with a simple reader macro:
;; args -> expression ===> (lambda args expression)
;;;;;;;;;;

(syntax (Lambda <- (/ Symbol List) (: "->") Expression)
  `(,(car Lambda)
    ((lambda ,(caadr Lambda) ,(cadadr Lambda)))))

;; Interaction with other rules clearly visible:
(syntax (Expression <- (/ Lambda Atom List)))

(Expression "(let ((sq (x) -> (* x x))) (sq 23))")
;; Parses to: (let ((sq (lambda (x) (* x x)))) (sq 23))