Resolving a token conflict in antlr

Question

I have a Token OR:'OR'; that I use for evaluating a boolean expression( a==b OR a==c) I have another rule for parsing state abbreviation that are in a char list AZ,AK,OR,GA... What I am finding is that antlr has error on the state list thinking OR should be an `or` token rather then ``` stateName : CHAR CHAR (','|EOF) ->^(STATE CHAR+) ; ``` how would I go about resolving this ambiguity? here are some of the rules I am trying to parse - THEN STATE_LICENSE AL,AK,AS,AZ,AR,CT,DE,DC,FM,FL,GA,GU,HI,ID,IL,IN,IA,KS,KY,LA,ME,MH,MD,MA,MI,MN,MS,MO,MT,NE,NV,NH,NJ,NM,NY,NC,ND,MP,OH,OK,OR,PW,PA - IF 1198 == "x" OR 1190 != "x" THEN DISABLE 800 - IF 801 >= "1000000" THEN DISPLAY_ERROR "It's+too+expensive.+Go+and+get+cheaper+one+!!!" Here is the gramar that I am using ``` grammar PointFieldRule; options { //language = 'CSharp3'; output=AST; ASTLabelType=CommonTree; } tokens{ STATE; } rule : ifExpression? actionExpression EOF! ; ifExpression :'IF'! logicalConditionExpression ; logicalConditionExpressio…

Accepted Answer

The lexer creates tokens independently from the parser. So it doesn't matter if the parser might "need" two `CHAR` tokens at a given point, if the lexer "sees" the text `"OR"`, it will always create a `BigOR` token. There's nothing you can do about that.

In your case, you can simply let `stateName` match two `CHAR` tokens, or a single `OR` token like this:

```
stateName   
 : name (','|EOF) ->^(STATE name)
 ;

name
 : CHAR CHAR
 | BigOR
 ;
```

Parsing input `"THEN STATE_LICENSE AL,OR,PA"` will result in the following AST:

Note that the `OR` is a single token, unlike the others, whose type are `CHAR` and have their chars separated. If you want your `OR` node to behave like that too, do something like this:

```
name
 : CHAR CHAR
 | BigOR     -> CHAR[""+$BigOR.text.charAt(0)] CHAR[""+$BigOR.text.charAt(1)]
 ;
```

resulting in:

Or if you want the two separate chars to be concatenated, do:

```
name
 : (CHAR CHAR | BigOR) -> CHAR[$text]
 ;
```

resulting in:

Resolving a token conflict in antlr

Solution

Problem