CODEWITHSUNDEEP
macrosracket
user3855664
user3855664

Reputation: 69

In a custom Racket language, how can I define a recursive macro?

I am trying to create a recursive macro in a custom Racket language. However, while the macro expands properly with #lang racket, it fails when implemented with my new language.

For example, here is the recursive definition of a simple macro f which expands to its last argument:

;; my-lang.rkt
#lang racket

(provide #%datum
         #%module-begin
         define-syntax
         (for-syntax syntax-case
                     syntax
                     raise-syntax-error
                     #%app
                     quote
                     #%datum))

#lang s-exp "my-lang.rkt"

(define-syntax (f stx)
  (syntax-case stx ()
    [(_ x) #'x]
    [(_ x xs ...) #'(f xs ...)]
    [_ (raise-syntax-error 'f "bad syntax" stx)]))


(f 1 2 3) ; =>  f: bad syntax in: (f 2 3)

Why isn't (f 2 3) matched and expanded?

Upvotes: 2

Views: 135

Answers (1)

soegaard
soegaard

Reputation: 31147

Add ... to the provided identifiers.

#lang racket
(provide #%datum
         #%module-begin
         define-syntax

         (for-syntax syntax-case
                     syntax
                     raise-syntax-error
                     #%app
                     quote
                     quote-syntax
                     ...
                     #%datum))

Upvotes: 1

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