Fix comments in REPL - fixes #78

Before this change, entering a comment in the REPL caused the REPL to
read the comment indefinitely effectively breaking it.

After this change the behaviour is the same as pypy.  The cpython
behaviour is slightly different printing a '...' after a comment line.
This is rather illogical and difficult to emulate properly.

Author: ncw

repl/repl.go

@@ -82,9 +82,13 @@ func (r *REPL) Run(line string) {
 		// FIXME detect EOF properly!
 		errText := err.Error()
 		if strings.Contains(errText, "unexpected EOF while parsing") || strings.Contains(errText, "EOF while scanning triple-quoted string literal") {
-			r.continuation = true
-			r.previous += string(line) + "\n"
-			r.term.SetPrompt(ContinuationPrompt)
+			stripped := strings.TrimSpace(toCompile)
+			isComment := len(stripped) > 0 && stripped[0] == '#'
+			if !isComment {
+				r.continuation = true
+				r.previous += string(line) + "\n"
+				r.term.SetPrompt(ContinuationPrompt)
+			}
 			return
 		}
 	}

repl/repl_test.go

@@ -67,6 +67,14 @@ func TestREPL(t *testing.T) {
 
 	r.Run("if")
 	rt.assert(t, "compileError", NormalPrompt, "Compile error: \n  File \"<string>\", line 1, offset 2\n    if\n\n\nSyntaxError: 'invalid syntax'")
+
+	// test comments in the REPL work properly
+	r.Run("# this is a comment")
+	rt.assert(t, "comment", NormalPrompt, "")
+	r.Run("a = 42")
+	rt.assert(t, "comment continuation", NormalPrompt, "")
+	r.Run("a")
+	rt.assert(t, "comment check", NormalPrompt, "42")
 }
 
 func TestCompleter(t *testing.T) {