In article <199601052019.OAA01671@europa.cs.rice.edu>,
Shriram Krishnamurthi <email@example.com> wrote:
>Paul Wilson wrote:
>> (John Ellis?) did a Lisp shell several years ago, where any
>> unbound function name was assumed to be an indication that
>> the programmer meant to call a UNIX program. [...]
>I thought (I'm about 800 miles from my Scsh docs ...) Olin explicitly
>wrote about this in his document (in the Tao section?). I agree with
>Olin on this front. One of the reasons I would even be interested in
>this command system is to integrate the two environments cleanly. To
>then make commands dependent on the environment strikes me as a stride
>in the wrong direction.
>To resolve the situation, I could live with the language _defaulting_
>in the other direction (ie, unless stated otherwise, the Unix
>namespace is used), but even this strikes me as undesirable.
>Personally, I know that if I could combine the two environments, most
>of what I run would, in fact, be from the Scheme environment (much of
>it, undoubtedly, chaining off eventually to something from Unix), and
>the number of actual raw Unix commands I would use would be few.
I'd say that if there's a terse/Scheme split along the lines Olin
recommends, the terse mode should default to running UNIX programs,
but the Scheme mode should not.
Either way, there should be a clean abstraction of how this works,
and a clean way of toggling it.
For example, suppose we represent the UNIX environment as a Scheme
module, with the funny property that it defaults to looking things
up as UNIX programs in the UNIX path, if it can't find a normal
There could be a "with" form that brings a module into scope, and
exiting that form would make the module inaccessible again.
That way, in a local segment of your program, you can switch on
the default-to-unix property, without the unsafety of that mode
infecting your whole program.
(foo bar) ; will not see a UNIX foo program if we forgot to define foo
(if (file-exists? "foo")
(rm foo)) ; will see the UNIX rm command, backquote its args
(display "couldn't find foo, so couldn't delete it")))
(quux baz) ; UNIX is out of scope again now
or in tersified, reduced-parens syntax, something like
if file-exists? "foo"
then rm foo
else display "couldn't find foo, so couldn't delete it"
| Paul R. Wilson, Comp. Sci. Dept., U of Texas @ Austin (firstname.lastname@example.org)
| Papers on memory allocators, garbage collection, memory hierarchies,
| persistence and Scheme interpreters and compilers available via ftp from
| ftp.cs.utexas.edu, in pub/garbage (or http://www.cs.utexas.edu/users/wilson/)