syntax for creating empty n-dimensional arrays

[simeonschaub]

These currently throw an error:

julia> [;]
ERROR: syntax: unexpected ";"
Stacktrace:
 [1] top-level scope
   @ none:1

julia> [;;]
ERROR: syntax: unexpected ";"
Stacktrace:
 [1] top-level scope
   @ none:1

julia> [;;;]
ERROR: syntax: unexpected ";"
Stacktrace:
 [1] top-level scope
   @ none:1

I think it would make sense for them to return an empty vector/0×0 matrix/0×0×0 array respectively.

[BioTurboNick]

I don't have time to implement it myself right now, but I looked into it:

[;] makes it into parse-cat and then the token stream is sent into parse-eq to determine the first value. The error originates inside parse-eq. Perhaps just need to check if the first value is a semicolon? Could set first to null, send it into parse-array. I'm not sure what parse-array would do when first is null, but I'm guessing it might generate (or could be made to generate) the syntax vect, ncat 2, ncat 3, with no contents. Then expand-ncat in julia-syntax.scm may need to check if a is null, or the helper functions all need to be made aware of the potential for a could be null (hasrows-flatten, is-1d). is-1d should return true, which would lower into hvncat(2), hvncat(3), which with #41197 will produce the desired output.

[StefanKarpinski]

Nice idea. This would "only" leave us with no literal syntax for empty zero-dimensional arrays, but fortunately there is no such thing!