Fix syntax error messages so that it never shows the underscore varia…

…ble.

TODO

@@ -1,5 +1,3 @@
-* Make stdin work
-* Fix error message resulting of syntax like: require 'date;
 * Make sure the following formatters work: hirb, awesome_print, and looksee
 * Make sure the majority of the utils in utility_belt work
 * Possibly add copy-paste support as an ext

lib/irb/context.rb

@@ -34,6 +34,7 @@ def initialize(object, explicit_binding = nil)
       @line    = 1
       clear_buffer
 
+      @underscore_assigner = __evaluate__("_ = nil; proc { |val| _ = val }")
       @processors = self.class.processors.map { |processor| processor.new(self) }
     end
 
@@ -42,7 +43,8 @@ def __evaluate__(source, file = __FILE__, line = __LINE__)
     end
 
     def evaluate(source)
-      result = __evaluate__("_ = (#{source})", '(irb)', @line - @source.buffer.size + 1)
+      result = __evaluate__(source.to_s, '(irb)', @line - @source.buffer.size + 1)
+      store_result(result)
       puts formatter.result(result)
       result
     rescue Exception => e
@@ -108,6 +110,10 @@ def formatter
     def clear_buffer
       @source = Source.new
     end
+
+    def store_result(result)
+      @underscore_assigner.call(result)
+    end
   end
 end
 

spec/regression/context_spec.rb

@@ -0,0 +1,16 @@
+require File.expand_path('../../spec_helper', __FILE__)
+
+main = self
+
+describe "IRB::Context, when evaluating source" do
+  before do
+    @context = IRB::Context.new(main)
+    def @context.printed;      @printed ||= ''          end
+    def @context.puts(string); printed << "#{string}\n" end
+  end
+
+  it "does not assign the result to the `_' variable in one go, so it doesn't show up in a syntax error" do
+    @context.evaluate("'banana;")
+    @context.printed.should.not.include "_ = ('banana;)"
+  end
+end