Add if-else statements

grammar.coffee

@@ -37,7 +37,11 @@ module.exports = compiler.grammar
     if_statement: -> seq(
       keyword("if"),
       "(", err(@expression), ")",
-      @statement)
+      @statement,
+      optional(seq(
+        keyword("else"),
+        @statement
+      )))
 
     switch_statement: -> seq(
       keyword("switch"),

grammar_test/statements.txt

@@ -23,6 +23,36 @@ if (a.b) {
       (expression_statement (function_call
         (identifier) (arguments (identifier)))))))
 
+============================================
+If-else statements
+============================================
+
+if (x)
+  y();
+else if (a)
+  b();
+
+if (a) {
+  c();
+  d();
+} else {
+  e();
+}
+
+----
+
+(program
+  (if_statement (identifier)
+    (expression_statement (function_call (identifier)))
+    (if_statement (identifier)
+      (expression_statement (function_call (identifier)))))
+  (if_statement (identifier)
+    (statement_block
+      (expression_statement (function_call (identifier)))
+      (expression_statement (function_call (identifier))))
+    (statement_block
+      (expression_statement (function_call (identifier))))))
+
 ============================================
 For statements
 ============================================