Questions

  • Homework questions?
  • Anyone else gotten started on the one from yesterday?
  • Look for test code

Parameter Passing Conventions

Today we implement 4, 4 interpreters, which exhibit different parameter-passing conventions.

Preludes: Boxes

> (box 'cat)
#&cat
> (define b (box 'cat))
> b
#&cat
> (unbox b)
cat
> b
#&cat
> (set-box! b 'dog)
> b
#&dog
>

All problems in computer science can be solved by another level of indirection. – David Wheeler

Call-by-value interpreter, revisited

We will at first revisit this interpreter, and a short-circuit line. This is for a derivation, not initially motivated in and of itself. But you could imagine wanting this, if you know this situation happens often.

Call-by-reference interpreter

Notice!

> (define b (box 'cat))
> (define c (box (unbox b)))
> (eqv? b c)
#f

Call-by-name interpreter

Call-by-need interpreter

                Strict evalutation   Non-strict evaluation   Passes new box    CBV (the standard)      Passes same box   CBReference          CBName   ----------------- -------------------- -----------------------

And our call-by-need interpreter is a variation on the CBName one, that uses the side-effect for efficiency.

See the lecture notes deriving these four interpreters to refresh and recapitulate.

Updated: