CODEWITHSUNDEEP
antlrantlr4visitor-pattern
László Halász
László Halász

Reputation: 438

Antlr visitor method is never called

I tried to create a simple language, which can evaluate if/else if/else statements and some arithmetic operations with predefined constans. The definition is the following:

grammar test;

ifStatement
:
    ifPart elseIfPart* elsePart
;

ifPart
:
    'if (' logicalExpression ') then ' retVal=basicElement
;

elseIfPart
:
    ' else if (' logicalExpression ') then ' retVal=basicElement
;

elsePart
:
    ' else ' retVal=basicElement
;

logicalExpression 
:
    logicalExpression ' and ' logicalExpression #andLogicalExpression
    |logicalExpression ' or ' logicalExpression #orLogicalExpression
    | compareExpression #compareLogicalExpression
    | '(' logicalExpression ')' #parensLogicalExpression
;

compareExpression
:
    basicElement '' basicElement #gt
    | basicElement '=' basicElement #eq
;


basicElement
:
    operation
    | atomicElement
;

operation
:
    operation op=('*'|'/') operation #mulDiv |
    operation op=('+'|'-') operation #addSub |
    atomicElement #atomic |
    '(' operation ')' #operationParens
;

atomicElement
:
    INT #decimal
    | 'resVal1' #reservedVariable
    | 'resVal2' #reservedVariable
;

INT
:
    [-]?[0-9]+('.'[0-9]+)? 
;

WS
:
    [ \t\r\n]+ -> skip
; // skip spaces, tabs, newlines

I generated a Visitor and a created a test sentence, which is the following:

    if (3+3=6 or 12*3=37) then 10*10 else 4+1

It returns 5, which is wrong. After some debugging I saw that the visitOrLogicalExpression method is never called, instead of it the visitCompareLogicalExpression is called two times. What is wrong with my language definition?

Thank You in advance!

Upvotes: 0

Views: 266

Answers (1)

László Halász
László Halász

Reputation: 438

The language definition was ok. I could fix the mentioned problem by modifying the Visitor class.

In the visitIfPart and visitElseIfPart methods (which process the subtrees of the if and else if nodes) I had to change the visitChildren(ctx.logicalExpression()) method to visitLogicalExpression(ctx.logicalExpression()), thus my code was able to catch the compound logical expressions.

Upvotes: 1

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