34 lines
1.2 KiB
Plaintext
34 lines
1.2 KiB
Plaintext
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;--- super if macro
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; This macro allow the following forms:
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; (If a then b) ==> (cond (a b))
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; (If a thenret) ==> (cond (a))
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; (If a then b else c) ==> (cond (a b) (t c))
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; (If a then b b2 ==> (cond (a b b2) (c d d2) (t e))
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; elseif c then d d2
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; else e)
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;
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;
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(defun If macro (lis)
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(prog (majlis minlis revl)
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(do ((revl (reverse lis) (cdr revl)))
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((null revl))
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(cond ((eq (car revl) 'else)
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(setq majlis `((t ,@minlis) ,@majlis)
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minlis nil))
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((or (eq (car revl) 'then) (eq (car revl) 'thenret))
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(setq revl (cdr revl)
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majlis `((,(car revl) ,@minlis) ,@majlis)
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minlis nil))
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((eq (car revl) 'elseif))
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((eq (car revl) 'If)
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(setq majlis `(cond ,@majlis)))
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(t (setq minlis `( ,(car revl) ,@minlis)))))
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; we displace the previous macro, that is we actually replace
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; the if list structure with the corresponding cond, meaning
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; that the expansion is done only once
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(rplaca lis (car majlis))
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(rplacd lis (cdr majlis))
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(return majlis)))
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;--- msg : print a message consisting of strings and values
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