[Grace-core] fixing REPL's

[Kim Bruce]

Andrew,

Sounds good to me, but I thought you were the one concerned about interpreting REPLs.  If it is all just sitting in a general (completed) object, then it shouldn't be a problem.  Of course we do need a way of stepping through an execution, but that's a bit off to the side.

Kim



On May 2, 2013, at 10:34 AM, Andrew P Black <andrew.p.black at gmail.com> wrote:

> I'm not impressed by the "nested scopes" idea for a dynamic language like Grace.  And we don't have teletypes any more, so we should be re-thinking "REPL", which implies that we do.  I like to think of a "play space" in which the student can edit and execute code.
> 
> It seems much more reasonable to me to treat the contents of the "play" window as a grace program, make it editable and executable, and make the semantics identical to what would be in a file.
> 
> In particular, the Grace equivalent of
> 
> Prelude> let sqr x = x * x
> Prelude> let sqq x = (sqr x) + 1
> Prelude> sqq 5
> 26
> 
> would be
> 
> 	method sqr(x) { x * x }
> 	method sqq(x) = { sqr(x) + 1 }
> 
> and that sqr(x) on the second line means self.sqr(x) — it's supposed to be dynamically bound.   So if the student re-defined sqr(x), she will expect the behaviour of sqq to change.
> 
> This can be made clear to the student by letting them EDIT the code in the "play" window, i.e., change the definition of method sqr rather than typing another one.
> 
> 	Andrew
> 
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