Hi Lindsay,
> I am surprised that 'prog works. Why, in this context, does it treat it's
> argument as 'data'?
Because there is no difference between code and data ;)
I think it becomes easily understandable, if you consider what 'prog' does:
(prog (foo) (bar))
Viewed as code, it *executes* first (foo), then (bar), and returns whatever
(bar) returned.
But in fact 'prog' is nothing more than a function which *evaluates* its
arguments in the normal way (here (foo) and (bar)), and which happens to return
the value of the last argument.
So for a single-argument case (prog (foo)) you have the identity function.
: (prog 123)
-> 123
: (prog (+ 3 4))
-> 7
> Given (NIL NIL NIL ("s" "p" "a" "a" "a" "c" "e" "s" ",") ....
>
> : (prog NIL)
> -> NIL
>
> : (prog ("s" "p" "a" "a" "a" "c" "e" "s" ","))
> !? ("s" "p" "a" "a" "a" "c" "e" "s" ",")
> "s" -- Undefined
Here 'prog' is called with a single argument, and expects the CAR to be a
function.
> ? (prog '("s" "p" "a" "a" "a" "c" "e" "s" ","))
> -> ("s" "p" "a" "a" "a" "c" "e" "s" ",")
This is fine, as the single argument is (quote "s" "p" ...) where 'quote' is a
function.
♪♫ Alex
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