clisp converting between infix, postfix, prefix (i'm trying if statements)

Question

I'm using CLISP and am trying

(if ( = (first '(+ 2 3)) + ) 10 20) //10 and 20 are just placeholders

I am trying to create a program that converts between infix, postfix, and prefix. I believe that my first step should be finding the symbols +, -, *, and / in the string. There will be no parentheses in the input. So, i am trying to search for each symbol systematically. the advantage of my approach is the ability to prioritize * over + etc.

I have a general idea of my approach, but any thoughts would be nice. my first idea is:

(append (rest '(+ 2 3)) (list (first '(+ 2 3))))

and yes, i plan on using recursion.

i have solved my own question. using "eq" instead of "=" helped. — Ankit Ahuja, May 07 '12 at 19:43

score 0 · Accepted Answer · edited May 23 '17 at 11:56

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some more googling brought me to What's the difference between eq, eql, equal, and equalp in Common Lisp? so i decided to implement "eq" instead of "=" and it worked just as expected.

edited May 23 '17 at 11:56

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answered May 09 '12 at 00:40

Ankit Ahuja

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Typically, you want to use EQL instead of EQ, except for the (very few) cases where you actually want to use EQ. – Vatine May 10 '12 at 03:57

clisp converting between infix, postfix, prefix (i'm trying if statements)

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