starlark: API additions for improved debugging (#76)

This change adds a number of small features to improve debugging.
The actual debugger API will come in a later change.

- Thread.Name : an optional string field that describes the purpose of
  the thread, for use in debugging.
- (*Program).Filename: a method that reports the file of the program.
  Also, a String method that returns the same thing.
  Also, a test that it reports the correct location even for
  an empty file (a special case of the previous implementation).
- (*Frame).Local(i int): a method to return the value of a local
  variable of an active frame, such as one might use in debugger's
  stack trace.
- ExprFunc: creates a starlark.Function from a given expression,
  such as one might use in a debugger REPL.

1 files changed, 1 insertions, 1 deletions

diff --git a/repl/repl.go b/repl/repl.go
index feccbe4..f90313e 100644
--- a/repl/repl.go
+++ b/repl/repl.go
@@ -215,7 +215,7 @@ func MakeLoad() func(thread *starlark.Thread, module string) (starlark.StringDic
 			cache[module] = nil
 
 			// Load it.
-			thread := &starlark.Thread{Load: thread.Load}
+			thread := &starlark.Thread{Name: "exec " + module, Load: thread.Load}
 			globals, err := starlark.ExecFile(thread, module, nil, nil)
 			e = &entry{globals, err}