Framework cannot handle languages with simple list of terminals

[akeep]

@LeifAndersen reported that a nanopass language with a simple list of expressions does not handle creating a list with no elements in it, even though this should be handled without a problem.

@LeifAndersen has a solution in the nanopass/nanopass-framework-racket, however, things have drifted enough that I'll need to adapt the solution a bit.

Here is the example:

(define-language Lsrc 
  (terminals
    (symbol (s))) 
  (Expr (e) 
    s
    (e* ...)))

(with-output-language (Lsrc Expr) `()) => '()

But should produce an Expr with an empty list in it.

[amirouche]

How to workaround that problem?

[akeep]

If you wan this syntax, there really isn't a work around for this. You can always add a keyword in the language:

(define-language Lsrc
  (terminals
    (symbol (s)))
  (Expr (e)
    s
    (list e* ...)))

For instance, will produce the expected language form in all cases:

> (with-output-language (Lsrc Expr) `(list a b c))
#[#{Lsrc:list:Expr.6 dykr8jd2wmthrm6w7m6embc8t-26} 2 (a b c)]
> (with-output-language (Lsrc Expr) `(list))
#[#{Lsrc:list:Expr.6 dykr8jd2wmthrm6w7m6embc8t-26} 2 ()]