On Mar 7, 2007, at 2:31 PM, AndrevanTonder wrote:
On Wed, 7 Mar 2007, William D Clinger wrote:
AndrevanTonder wrote:
Granted, but what does this have to do with being an interpreter
or not?
"Pure" is the operative word.
[...]
Maybe I do not understand what is meant by "pure".
A pure interpreter here (I guess) is one that does not perform *any*
work (other than reading the program perhaps) on the program prior to
evaluating it. So, for example, an (impure?) interpreter may
"compile" a reference to a variable X to one of the following:
- if X is an identifier-syntax, call the transformer and re-expand
the residual expression.
- if X is a global reference, mark it as such.
- if X is a lexical variable, compute its position in the lexical
environment.
and so on. A "pure" interpreter, on the other hand, does none of
this business prior to evaluation (it just interprets source-level s-
expressions; plain and simple). I'm actually surprised to see this
used in anything other than a homework assignment for junior-level
course on programming languages.
Aziz,,,
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