Added if statement

src/main/antlr4/de/hsrm/compiler/Klang/Klang.g4

@@ -8,27 +8,47 @@ block
   : statement*
   ;
 
+braced_block
+  : OBRK statement* CBRK
+  ;
+
 statement
   : print
+  | if_statement
   ;
 
 print
   : PRINT expression SCOL
   ;
 
+if_statement
+  : IF expression THEN braced_block (ELSE braced_block)?
+  ;  
+
 expression
   : atom MULT atom #multiplicationExpression
   | atom op=(ADD | SUB) atom #additiveExpression
   | atom MOD atom #moduloExpression
   | SUB atom #unaryNegateExpression
+  | atom #atomExpression
   ;
 
 atom
   : INTEGER_LITERAL #intAtom
   ;
 
+/*
+  if 5 = 5 then whatever else whatever
+ */
+
 PRINT: 'print';
+IF: 'if';
+THEN: 'then';
+ELSE: 'else';
+
 SCOL: ';';
+OBRK: '{';
+CBRK: '}';
 
 MULT: '*';
 ADD: '+';