Hi all,
while talking about 'set' and 'setq', let me clarify another issue. Quite often
I see here - or in IRC - expressions like
(mapc 'set '(A B C) (1 2 3))
or
(mapcar 'inc (4 5 6))
While this certainly works, it is actually wrong, or at least unnecessary.
The mapping functions want a *functional* first argument. If you look up in the
reference (under "Evaluation", doc/ref.html#ev), it says that a function is
either a number (a function pointer) or a cell (with parameter(s) in the CAR and
a 'prg' body in the CDR).
However, the above expressions pass a *symbol* to the mapping functions. So just
(mapc set '(A B C) (1 2 3))
or
(mapcar inc (4 5 6))
would be fine, because the first arguments are evaluated, resulting in proper
numbers.
The quoted calls (resulting in symbols) happen to work just due to a lucky
coincidence:
When PicoLisp evaluates a function call, it tries to be tolerant. Instead of
throwing an error when hitting a symbol, it *evaluates* that symbol (or any
expressions in general which show up, until it gets to a proper function. For
example
(de square (N)
(* N N) )
(setq
F 'square )
L '(line square circle) )
: (F 7)
-> 49
: ((cadr L) 7)
-> 49
: ((val (cadr L)) 7)
-> 49
One more note: In case of *message* calls on objects you *must* pass a symbol.
They need a symbol to locate the right method in the class hierarchy
(mapc 'lose> (collect 'key '+Cls))
so here the quote is correct.
- Alex
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