Code added.

.gitignore

@@ -10,3 +10,6 @@
 
 # virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
 hs_err_pid*
+/target
+/rule-compiler.iml
+/.idea

pom.xml

@@ -0,0 +1,75 @@
+<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>
+
+  <groupId>me.ivanyu</groupId>
+  <artifactId>rule-compiler</artifactId>
+  <version>1.0-SNAPSHOT</version>
+  <packaging>jar</packaging>
+
+  <name>rule-compiler</name>
+  <url>http://maven.apache.org</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.11</version>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>com.fasterxml.jackson.core</groupId>
+      <artifactId>jackson-annotations</artifactId>
+      <version>2.3.0</version>
+    </dependency>
+    <dependency>
+      <groupId>com.fasterxml.jackson.core</groupId>
+      <artifactId>jackson-databind</artifactId>
+      <version>2.3.3</version>
+    </dependency>
+    <dependency>
+      <groupId>com.fasterxml.jackson.core</groupId>
+      <artifactId>jackson-core</artifactId>
+      <version>2.3.1</version>
+    </dependency>
+
+    <dependency>
+      <groupId>org.antlr</groupId>
+      <artifactId>antlr4-runtime</artifactId>
+      <version>4.3</version>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.antlr</groupId>
+        <artifactId>antlr4-maven-plugin</artifactId>
+        <version>4.3</version>
+        <executions>
+          <execution>
+            <goals>
+              <goal>antlr4</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.1</version>
+        <configuration>
+          <source>1.7</source>
+          <target>1.7</target>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

src/main/antlr4/me/ivanyu/RuleSetGrammar.g4

@@ -0,0 +1,92 @@
+grammar RuleSetGrammar;
+
+/* Lexical rules */
+
+IF   : 'if' ;
+THEN : 'then';
+
+AND : 'and' ;
+OR  : 'or' ;
+
+TRUE  : 'true' ;
+FALSE : 'false' ;
+
+MULT  : '*' ;
+DIV   : '/' ;
+PLUS  : '+' ;
+MINUS : '-' ;
+
+GT : '>' ;
+GE : '>=' ;
+LT : '<' ;
+LE : '<=' ;
+EQ : '=' ;
+
+LPAREN : '(' ;
+RPAREN : ')' ;
+
+// DECIMAL, IDENTIFIER, COMMENTS, WS are set using regular expressions
+
+DECIMAL : '-'?[0-9]+('.'[0-9]+)? ;
+
+IDENTIFIER : [a-zA-Z_][a-zA-Z_0-9]* ;
+
+SEMI : ';' ;
+
+// COMMENT and WS are stripped from the output token stream by sending
+// to a different channel 'skip'
+
+COMMENT : '//' .+? ('\n'|EOF) -> skip ;
+
+WS : [ \r\t\u000C\n]+ -> skip ;
+
+
+/* Parser rules */
+
+rule_set : single_rule* EOF ;
+
+single_rule : IF condition THEN conclusion SEMI ;
+
+condition : logical_expr ;
+conclusion : IDENTIFIER ;
+
+logical_expr
+ : logical_expr AND logical_expr # LogicalExpressionAnd
+ | logical_expr OR logical_expr  # LogicalExpressionOr
+ | comparison_expr               # ComparisonExpression
+ | LPAREN logical_expr RPAREN    # LogicalExpressionInParen
+ | logical_entity                # LogicalEntity
+ ;
+
+comparison_expr : comparison_operand comp_operator comparison_operand
+                    # ComparisonExpressionWithOperator
+                | LPAREN comparison_expr RPAREN # ComparisonExpressionParens
+                ;
+
+comparison_operand : arithmetic_expr
+                   ;
+
+comp_operator : GT
+              | GE
+              | LT
+              | LE
+              | EQ
+              ;
+
+arithmetic_expr
+ : arithmetic_expr MULT arithmetic_expr  # ArithmeticExpressionMult
+ | arithmetic_expr DIV arithmetic_expr   # ArithmeticExpressionDiv
+ | arithmetic_expr PLUS arithmetic_expr  # ArithmeticExpressionPlus
+ | arithmetic_expr MINUS arithmetic_expr # ArithmeticExpressionMinus
+ | MINUS arithmetic_expr                 # ArithmeticExpressionNegation
+ | LPAREN arithmetic_expr RPAREN         # ArithmeticExpressionParens
+ | numeric_entity                        # ArithmeticExpressionNumericEntity
+ ;
+
+logical_entity : (TRUE | FALSE) # LogicalConst
+               | IDENTIFIER     # LogicalVariable
+               ;
+
+numeric_entity : DECIMAL              # NumericConst
+               | IDENTIFIER           # NumericVariable
+               ;

src/main/java/me/ivanyu/CompilerApplication.java

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+package me.ivanyu;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import me.ivanyu.compiler.Compiler;
+import me.ivanyu.pojos.RuleSet;
+
+public class CompilerApplication {
+    public static void main(String[] args) {
+        Compiler compiler = new Compiler();
+        RuleSet ruleSet = compiler.compile("if -(A + 2) > 0.5 then be_careful;");
+
+       // JSON serialization
+        ObjectMapper mapper = new ObjectMapper();
+        mapper.enable(SerializationFeature.INDENT_OUTPUT);
+
+        String jsonString = null;
+        try {
+            jsonString = mapper.writeValueAsString(ruleSet);
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        }
+        System.out.println(jsonString);
+    }
+}

src/main/java/me/ivanyu/compiler/Compiler.java

@@ -0,0 +1,25 @@
+package me.ivanyu.compiler;
+
+import me.ivanyu.RuleSetGrammarLexer;
+import me.ivanyu.RuleSetGrammarParser;
+import me.ivanyu.pojos.RuleSet;
+import org.antlr.v4.runtime.ANTLRInputStream;
+import org.antlr.v4.runtime.CommonTokenStream;
+import org.antlr.v4.runtime.TokenStream;
+
+public class Compiler {
+    public RuleSet compile(String inputString) {
+        ANTLRInputStream input = new ANTLRInputStream(inputString);
+        RuleSetGrammarLexer lexer = new RuleSetGrammarLexer(input);
+        TokenStream tokens = new CommonTokenStream(lexer);
+        RuleSetGrammarParser parser = new RuleSetGrammarParser(tokens);
+
+        TreeBuilder treeBuilder = new TreeBuilder();
+        parser.addParseListener(treeBuilder);
+        parser.setErrorHandler(new ExceptionThrowingErrorHandler());
+
+        parser.rule_set();
+
+        return treeBuilder.getRuleSet();
+    }
+}

src/main/java/me/ivanyu/compiler/ExceptionThrowingErrorHandler.java

@@ -0,0 +1,22 @@
+package me.ivanyu.compiler;
+
+import org.antlr.v4.runtime.*;
+
+/**
+ * Error handler which throws exception on any parsing error.
+ */
+public class ExceptionThrowingErrorHandler extends DefaultErrorStrategy {
+    @Override
+    public void recover(Parser recognizer, RecognitionException e) {
+        throw new RuntimeException(e);
+    }
+
+    @Override
+    public Token recoverInline(Parser recognizer) throws RecognitionException {
+        throw new RuntimeException(new InputMismatchException(recognizer));
+    }
+
+    @Override
+    public void sync(Parser recognizer) throws RecognitionException {
+    }
+}