Errors in parsed code produce confusing error messages

[jandrewb]

The following code produces a confusing error message:

var foo = 100; foo();

Actual: 'TypeError: 100 is not a function' Expected: 'TypeError: foo is not a function'

The only problem is that the error message uses the value of 'foo' rather than its name. Fixing this would make debugging parsed code much less confusing.

[cpcallen]

I'm interested in improving error messages in JS Interpreter (or rather: in a heavily modified fork of it I maintain). If you have any insight into how other interpreters produce better error messages in cases like this I would be most interested in knowing more.