add rspec for parser

spec/zodiac/parser_spec.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require './spec/spec_helper'
+require './src/zodiac/parser'
+
+describe Zodiac::Parser do
+  describe '.parse' do
+    context 'when empty program' do
+      it 'returns empty program' do
+        parser = described_class.new('')
+
+        actual = parser.parse
+        expected = { kind: 'PROGRAM', value: [] }
+
+        expect(actual).to eq(expected)
+      end
+    end
+  end
+end

src/zodiac/parser.rb

@@ -197,13 +197,19 @@ def initialize(raw_string)
       @tokens = []
     end
 
-    def parse; end
+    def parse
+      parse_program
+    end
 
     private
 
     # PROGRAM		: COMPSTMT
     def parse_program
-      { kind: 'PROGRAM', value: parse_compstmt }
+      cmp_stmts = []
+
+      cmp_stmts << parse_compstmt while @cur_index < @raw_string.length
+
+      { kind: 'PROGRAM', value: cmp_stmts }
     end
 
     # COMPSTMT	: STMT (TERM EXPR)* [TERM]