incremental definition (was Re: scoops & xscheme)

[William Clinger <uoregon!will@beaver.cs.washington.edu>]

Someone posted an example of unexpected interaction, or lack thereof,
between first class environments and incremental DEFINE (using EVAL) in
XScheme, and asked:

>   When  I  look  how  environments  are  implemented  I  can understand this
>behaviour  but  is  this  still  Scheme?

Neither EVAL nor THE-ENVIRONMENT are part of Scheme, so the fact that XScheme
happens to define procedures with those names that happen not to work the way
someone expects has no bearing on whether it is a real Scheme system.

Most people think it is better to think of incremental definitions as part
of a programming environment instead of a language, since they are primarily
used for debugging.  The programming environment obviously differs from one
implementation to another, so code that depends on the programming environment
is not portable.

William Clinger