/** Simple statically-typed programming language with functions and variables
 *  taken from "Language Implementation Patterns" book.
 */
grammar Hello;

file:    ((functionDecl | varDecl | stat )';')+   ;

varDecl
    :  ID ':' TYPE  ('<-' expr)?
    ;
TYPE :   'Float' | 'Int' | 'Void' | 'Bool' ;

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

formalParameters
    :   formalParameter (',' formalParameter)*
    ;
formalParameter
    :   ID ':' TYPE
    ;

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

stat:   block
    |   varDecl
    |   'if' expr 'then' stat ('else' stat)?

    |   expr '<-' expr ';' // assignment
    |   expr          // func call
    ;


expr:   ID '(' exprList? ')'    # Call
    |   expr '*' expr           # Mult
    |   expr PLUS expr          # Add
    |   expr MINUS expr           # Sub
    |   expr LT expr            # Less
    |   expr '=' expr          # Equal
    |   ID                      # Var
    |   INT                     # Int
    |   '(' expr ')'            # Parens
    ;

exprList : expr (',' expr)* ;   // arg list
ID  :   LETTER (LETTER | [0-9])* ;
fragment
LETTER : [a-zA-Z] ;

INT :   [0-9]+ ;

WS  :   [ \t\n\r]+ -> skip ;

PLUS: '+';
MINUS: '-';
LT: '<';
SL_COMMENT
    :   '//' .*? '\n' -> skip
    ;