How do you substitute AA but not AAA, AAAA, AAAAA etc.?

Andreas Larsen

    ignore sub A' A' A;
    sub A' A by A.alt;
    sub A A' by A.alt;

Doesn't work for AAAA, AAAAAA etc

Erwin Denissen

lookup ChainingContext1 {
  ignore context (A.alt) A (A);
  ignore context (A) A;
  context A (A);
  sub 0 Ligature1;
}

lookup Ligature1 {
  sub A -> A.alt;
}

Georg Seifert

What is the desired result?

Rainer Erich Scheichelbauer

The marked subrun (A' A') in the ignore statement differs from the subrun (A') in the sub statements. So the ignore does not apply to subs.

Kent Lew

If you only want to change the first two in a sequence, but not any subsequent repetitions, then this should work:

feature calt {
    ignore sub A.alt A.alt A';
    ignore sub A A';
    sub A' A by A.alt;
    sub A.alt A' by A.alt;
    } calt;

But if you want to change two and only two, and not any member of a longer sequence, then you need to add another ignore sub:

feature calt {
    ignore sub A.alt A.alt A';
    ignore sub A A';
    ignore sub A' A A;
    sub A' A by A.alt;
    sub A.alt A' by A.alt;
    } calt;

Andreas Larsen

@ everyone: Sorry, I should have been clearer:) 

What I want is:
A A -> A.alt A.alt
A A A -> A A A
A A A A -> A A A A
etc.

so not e.g. 
A A A -> A.alt A.alt A
A A A A -> A.alt A.alt A A

Inspired by the answers I've played around a bit and not the prettiest solution but this seem to work:

ignore sub A' A A;
ignore sub A A' A;
ignore sub A A A';
sub A' A by A.alt;
sub A A' by A.alt;

Georg Seifert

that shouldn't work. The last substitution is not possible as the first A is already substituted to A.alt by the time this line will be applied.

Andreas Larsen

@Georg Seifert Sorry, typo. Should be

ignore sub A' A A;
ignore sub A A' A;
ignore sub A A A';
sub A' A by A.alt;
sub A.alt A' by A.alt;

Nick Shinn

feature calt {

lookup first {

sub A A' by A.alt ;

} first;

lookup second {

sub A A.alt' A by A ;

} second;

} calt;

attar

You have to understand that substitutions are done one after the other, so when the first substitution is done subsequent substitutions need to be aware of what was previously changed.

Andreas Larsen

@Adrien Tétar Yep, I know - I typed it wrong:) Did you see my updated reply to Georg?

Andreas Larsen

@Nick Shinn Looks elegant but wouldn't that result in:

A A -> A A.alt

and not

A A -> A.alt A.alt

or am I missing something?

attar

I see it now, it should work.

Andreas Larsen

@Adrien Tétar Cheers. Figured that, since we posted at the same time:)

Kent Lew

Basically the same as my second example.

Andreas Larsen

@Kent Lew it sure is. I'm new to this...