Chaining module languages🔗 i

This package is experimental. Later versions may break backward-compatibility.

As an example here is the definition for a no-op language, which simply takes a (possibly improper) list of languages to chain, and calls the next one:

(module the-meta-langracket/base

(provide (rename-out [new-#%module-begin#%module-begin ]))

(require chain-module-begin

(for-syntax racket/base

syntax/parse))

(define-syntax (new-#%module-beginstx)

(syntax-parsestx

[(_ {~ornext-lang:id(next-lang:id. chain₊)}. body)

(define maybe-chain₊(if (attributechain₊)

`(,#'chain₊)

'()))

(define new-form`(,#'chain-module-begin ,#'next-lang,@maybe-chain₊

. ,(transform-body#'body)))

(datum->syntax stxnew-formstxstx)]))

(define-for-syntax (transform-bodybody)

;identity transformation:

body))

This language could then be used as follows:

(module bthe-meta-langtyped/racket

(define x:Number123))

Given two other meta-language built in the same way and provided by meta-two and meta-three, it would be possible to chain the three languages as follows:

(module bthe-lang(meta-twometa-three. typed/racket)

(define x:Number123))

The chain-module-begin macro produces the following syntax:

(#%plain-module-begin

(require lang)

(continue. internal-args))

where (continue. internal-args) fully expands (#%module-begin . body), where #%module-begin is the one provided by lang, and produces the following syntax:

(begin . expanded-body)

An extra scope is added to the whole (begin . expanded-body) form, so that a #%require form within the expanded-body may shadow bindings provided by lang, just as require forms normally have the possibility to shadow bindings provided by the #lang language.