parse functions using antlr4

[Santosh Kumar]

<code>

/** Simple statically-typed programming language with functions and variables

 *  taken from "Language Implementation Patterns" book.

 */

grammar Cymbol;

file:   (functionDecl | varDecl)+ ;

varDecl

    :   type ID ('=' expr)? ';'

    {/* System.out.print("var "+$ID.text+":"+$type.text+ " at line: " + $ID.line +";"); */}

    {/* System.out.println(" at pos: " + $ID.pos +";"); */}

    {/* System.out.println(" start: " + $start.getText() +";"); */ }

    {/* System.out.println(" stop: " + $stop.getText() +";"); */ }

    ;

type:   'float' | 'int' | 'void' ; // user-defined types

functionDecl

    :   type ID '(' formalParameters? ')' block // "void f(int x) {...}"

    { System.out.print("function: "+$type.text+" "+ $ID.text + " ( "+$formalParameters.text + " )" ) ; }

     {System.out.println(" block: " + $block.text +" ");}

    

     {/* System.out.print(" start: "+$type.text+" "+ $ID.text + " ( "+$start.getText() + " )" ) ;*/}

    {/* System.out.print(" at line: " + $ID.line +";");*/}

    {/*System.out.println(" at pos: " + $ID.pos +";");*/}

    ;

formalParameters

    :   formalParameter (',' formalParameter)*

    {  System.out.println(" -> formalParameter: "  +" " + $formalParameter.text  +";"); }

    ;

formalParameter

    :   type ID

    {  System.out.print(" formalParameter: "+$type.text+" "+ $ID.text + "\n") ; }

    ;

block:  '{' stat* '}' ;   // possibly empty statement block

stat:   block

    |   varDecl

    |   'if' expr 'then' stat ('else' stat)?

    |   'return' expr? ';' 

    |   expr '=' expr ';' // assignment

    |   expr ';'          // func call

    ;

expr:   ID '(' exprList? ')'    // func call like f(), f(x), f(1,2)

    |   ID '[' expr ']'         // array index like a[i], a[i][j]

    |   '-' expr                // unary minus

    |   '!' expr                // boolean not

    |   expr '*' expr

    |   expr ('+'|'-') expr

    |   expr '==' expr          // equality comparison (lowest priority op)

    |   ID                      // variable reference

    |   INT

    |   '(' expr ')'

    ;

exprList : expr (',' expr)* ;   // arg list

ID  :   LETTER (LETTER | [0-9])* ;

fragment

LETTER : [a-zA-Z] ;

INT :   [0-9]+ ;

WS  :   [ \t\n\r]+ -> skip ;

SL_COMMENT

    :   '//' .*? '\n' -> skip

    ;

</code>

<input>

int g = 9;        // a global variable

int   fact(int x, int j) { // factorial function

    if x==0 then return 1;

    return x * fact(x-1);

}

</input>

The output is not according to expectations. It concatenates int and x giving intx. How to fix this.

Thanks