Hi, all, do you guys know how to do "and" and "or" in lisp?

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akatsuki521
Posts: 1
Joined: Sun Nov 03, 2013 9:24 am

Hi, all, do you guys know how to do "and" and "or" in lisp?

Post by akatsuki521 » Sun Nov 03, 2013 9:27 am

I mean in the "if" and "cond". How to evaluate multiple conditions? Thx.

edgar-rft
Posts: 226
Joined: Fri Aug 06, 2010 6:34 am
Location: Germany

Re: Hi, all, do you guys know how to do "and" and "or" in li

Post by edgar-rft » Sun Nov 03, 2013 5:10 pm

See Peter Seibel's Practical Common Lisp, Chapter 7: Standard Control Constructs

sylwester
Posts: 133
Joined: Mon Jul 11, 2011 2:53 pm

Re: Hi, all, do you guys know how to do "and" and "or" in li

Post by sylwester » Mon Nov 04, 2013 11:52 am

cond is just a macro that ends up being nested ifs. It has implicit progn so a if where the consequent or alternative needs a progn or if it's more than one predicate simply looks better written as a cond.

Code: Select all

(macroexpand 
 '(cond ((test-predicate-function arg) (consequent1-with-sideeffect)
                             (consequent2-tail-call))
        (test-predicate-value consequent-value1)
        (t (alternative-expression))))

; ==> 

(if (test-predicate-function arg)
    (progn (consequent1-with-sideeffect) 
           (consequent2-tail-call))
    (if test-predicate-value 
        consequent-value1 
        (alternative-expression)))
and and or are macros that end up being nested ifs as well. Just use macroexpand to see the maging. (don't forget to quote the code or else it will try to expand the result)
I'm the author of two useless languages that uses BF as target machine.
Currently I'm planning a Scheme compiler :p

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