Dear members of the list,
I'm implementing language for science computations similar to Matlab. I found
Parrot to be the best
solution for that. Syntax of Matlab (which I'm trying to be compatible to)
isn't quite logical and
consistent, so I've faced some problems expressing it grammar in Perl 6 rules.
1. The language's control structures ('if', 'while', etc.) always ends with
keyword 'end'. It's
prohibited to use this reserved word for other purposes... except indexing!
It's allowed to use
it in array subscript to represent length of corresponding array dimension.
For example,
if <condition>
<block of code>
end
but
array(1, end - 3, 5) = 1
I didn't find any language's implementation in Parrot which handle similar
"feature". Currently
I can see only one way to implement this. In grammar, remove 'end' from
keywords list, and deny
single 'end' statement, so 'end' would be a normal identifier, but not a
single statement.
rule statement
{
<!statement_end>
[
| <statement_if> {*} #= statement_if
| <statement_while> {*} #= statement_while
# other types of statements here
]
}
token statement_end
{
'end' <.sep>
# <sep> is statement terminator token
}
In other cases, such as usual expressions, I could deny using of 'end'
identifier later in NQP.
I don't think this is a sane solution of my problem (I also understand that
this using of
keyword is not quite sane too). Is there a better way? Please let me know.
2. Due to Matlab compatibility the language also has inconsistent use of
whitespace. In most cases
whitespace is not important and can be easily ignored by <ws> rule. But
there is an exception
--- array constructor where it's used as delimiter between elements.
For example,
[ 1 2 3 ] three elements
[ 1 -2 3 ] still three elements
[ 1-2 3 ] two elements
[ 1- 2 ] one element
[ 1 - 2 ] again, one element
How whitespace matching behavior can be changed (for example, switched from
one meaning to
another inside and outside of expressions in array constructor) to parse
such a weird
constructions?
--
Igor V. Burago
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