Adding grammar file and pom.xml

Demo.g4

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+grammar Demo;
+
+program: programPart+;
+
+programPart: statement #MainStatement
+           | functionDefinition #ProgPartFunctionDefinition
+           ;
+
+statement : println ';'
+          | print ';'
+          | varDeclaration ';'
+          | assignment ';'
+          | branch
+          ;
+
+branch : 'if' '(' condition=expression ')' onTrue=block 'else' onFalse=block ;
+
+block : '{' statementList '}' ;
+
+expression: left=expression '/' right=expression #Div
+          | left=expression '*' right=expression #Mult
+          | left=expression '-' right=expression #Minus
+          | left=expression '+' right=expression #Plus
+          | left=expression operator=('<' | '<=' | '>' | '>=') right=expression #Relational
+          | left=expression operator='&&' right=expression #And
+          | left=expression operator='||' right=expression #Or
+          | number=NUMBER #Number
+          | txt=STRING #String
+          | varName=IDENTIFIER #Variable
+          | functionCall #FuncCallExpression
+          ;
+
+varDeclaration: 'int' varName=IDENTIFIER ;
+
+assignment: varName=IDENTIFIER '=' expr=expression ;
+
+println: 'println(' argument=expression ')' ;
+
+print: 'print(' argument=expression ')' ;
+
+functionDefinition: 'int' funcName=IDENTIFIER '(' params=parameters')' '{' statements=statementList 'return' retValue=expression ';' '}' ;
+
+statementList : (statement)* ;
+
+parameters:
+          | declarations+=varDeclaration (',' declarations+=varDeclaration)*
+          ;
+
+functionCall: funcName=IDENTIFIER '(' args=expressionList ')';
+
+expressionList:
+              | expressions+=expression (',' expressions+=expression)*
+              ;
+
+// Terminals
+IDENTIFIER: [A-Za-z][A-Za-z0-9]*;
+NUMBER: [0-9]+;
+WHITESPACE: [ \t\n\r]+ -> skip;
+STRING: '"' .*? '"';

pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <properties>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+    </properties>
+
+    <groupId>org.example</groupId>
+    <artifactId>antlr-compiler</artifactId>
+    <packaging>pom</packaging>
+    <version>1.0-SNAPSHOT</version>
+    <modules>
+        <module>parser</module>
+        <module>compiler</module>
+    </modules>
+
+    <dependencies>
+        <!-- https://mvnrepository.com/artifact/org.antlr/antlr4 -->
+        <dependency>
+            <groupId>org.antlr</groupId>
+            <artifactId>antlr4</artifactId>
+            <version>4.7.1</version>
+        </dependency>
+    </dependencies>
+
+</project>