Could a "slang" resolve this?

For some meanings of "resolve", I guess it could.
Though again there's a reason for why things are the way they are:

Allowing infix < without preceding space would conflict with the postcircumfix < > construct which is used in Perl 6 for indexing/slicing associative data structures (like hashes) with string keys.
As in %stuff<key> but not limited to explicit hash variables, i.e. it can follow arbitrary expressions:

$ perl6
> ('xx'..'zz').classify(*.substr(1))<z>
xz yz zz
> {aa => 11, bb => 22, cc => 33, dd => 44}<cc>
33
> %(<aa bb cc dd> Z=> (11, 22 ... *))<cc>
33
> sub foo { return {bar => 42} }
> foo<bar>
42

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I believe in the general case, the compiler simply replaces ...<key> with ...{'key'}, causing the { } postcircumfix operator to be dispatched on the return-value object of the preceding expression at run-time (or die with a run-time error if the operator is not defined for that object's type).

The problem with code like 1<2 is that (as far as I understand it) as soon as the parser sees the opening angle bracket sticking to the right of an expression, it assumes it found an instance of the < > postcircumfix and tries to parse the following text accordingly.
If the actual text there does not match that expectation, the parser aborts with a syntax error. In this case, the error handling code is smart enough to look at the surroundings and figure out that you probably meant to use the < infix operator (numeric comparison) there, so it prints that instead of a generic a "syntax error".

Now in theory the parser could be written so it would try both possibilities (postcircumfix < > and infix <) when it sees an angle bracket after an expression like that, and continue parsing both variants until one of them hits a syntax error down the road and can be eliminated.
But I'm pretty sure that would violate the design principle of keeping the Perl 6 grammar as deterministic and "self-clocking" as possible, which seems to be very important to Larry Wall (and for which authors of slangs/macros or of Perl 6 syntax highlighters / IDEs etc. will probably be grateful).

So if you want your slang to only change the meaning of those simple cases (< between two number literals) which the compiler's error handling code can already detect anyway, that would probably be reasonably safe, but if you also want expressions like $number<5 to be interpreted as numeric comparisons, that would likely lead to all kinds of parsing difficulties.

In reply to Re^2: Porting (old) code to something else by smls
in thread Porting (old) code to something else by Tux

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