add test for uninitialized vars

FossilOrigin-Name: 9b734dc92b4bca6a25fde30f556565d5a48a64f9a9531c89f2927f6674e82a70

ruby/lib/lox.rb

@@ -40,9 +40,7 @@ module Lox
 
     def run(src)
       super
-    rescue Lox::ParseError => e
-      STDERR.puts e.message
-    rescue Lox::RuntimeError => e
+    rescue Lox::ParseError, Lox::RuntimeError => e
       STDERR.puts e.message
     end
 

ruby/lib/lox/environment.rb

@@ -14,11 +14,13 @@ module Lox
     def get(token)
       name = token.lexeme
 
-      @values.fetch(name) {
-        raise RuntimeError.new(token, "Undefined variable '#{name}'.") if @enclosing.nil?
-
+      if @values.has_key?(name)
+        @values[name]
+      elsif @enclosing
         @enclosing.get(token)
-      }
+      else
+        raise RuntimeError.new(token, "Undefined variable '#{name}'.")
+      end
     end
 
     def assign(name, value)
@@ -26,15 +28,11 @@ module Lox
 
       if @values.has_key?(lexeme)
         @values[lexeme] = value
-        return
-      end
-
-      unless @enclosing.nil?
+      elsif @enclosing
         @enclosing.assign(name, value)
-        return
+      else
+        raise RuntimeError.new(name, "Undefined variable '#{lexeme}'.")
       end
-
-      raise RuntimeError.new(name, "Undefined variable '#{lexeme}'.")
     end
   end
 end

ruby/test/lox/test_interpreter.rb

@@ -150,13 +150,19 @@ class TestInterpreter < Lox::Test
     SRC
   end
 
+  def test_uninitialized_vars_are_nil
+    assert_interpreted <<~EXPECTED.chomp, <<~SRC
+      nil
+    EXPECTED
+      var a;
+      print a;
+    SRC
+  end
+
   private
 
   def assert_interpreted(expected, src)
-    output = with_stdout {
-      stmts = Lox::Parser.new(@scanner.scan(src)).parse!
-      @interpreter.interpret(stmts)
-    }
+    output = interpret(src)
     assert_equal expected, output
   end
 
@@ -175,4 +181,11 @@ class TestInterpreter < Lox::Test
     output
   end
 
+  def interpret(src)
+    with_stdout {
+      stmts = Lox::Parser.new(@scanner.scan(src)).parse!
+      @interpreter.interpret(stmts)
+    }
+  end
+
 end