2

I know it is possible to switch between the default and hidden token channels in an ANTLR grammar, but lets say I want a third channel. How can I define a new token channel in the gramar? For instance, lets say I want a channel named ALTERNATIVE.

icktoofay
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Matthew Sowders
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  • For anyone coming here in 2022 (I have 4.10) and being nonplussed about why the "channel name" trick as described in the ANTLR book is not accepted ("foo is not a recognized channel name" says ANTLR) see https://github.com/antlr/antlr4/issues/1555 - Custom channel names are no longer allowed in combined grammars (so use integers instead) and in lexer grammars, the syntax to define them is now `channels { FOO }`. – David Tonhofer Oct 29 '22 at 09:30

2 Answers2

2

They're just final int's in the Token class , so you could simply introduce an extra int in your lexer like this:

grammar T;

@lexer::members {
  public static final int ALTERNATIVE = HIDDEN + 1;
}

// parser rules ...

FOO
  :  'foo' {$type=ALTERNATIVE;}
  ;

// other lexer rules ...

A related Q&A: How do I get an Antlr Parser rule to read from both default AND hidden channel

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Bart Kiers
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1

For the C target you can use 

//This must be assigned somewhere
@lexer::context {
  ANTLR3_UINT32 defaultChannel;
}

TOKEN : 'blah' {$channel=defaultChannel;};

This gets reset after every rule so if you want a channel assignment to persist across rules you may have to override nextTokenStr().