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I’m new to ACL2 theorem prover. I want to update the value of a variable based on XOR result of three variables. I think “setq” will do that for me.

(setq out (xor (xor a b) c))

However, I get this error:

ACL2 Error in TOP-LEVEL: The symbol SETQ (in package "COMMON-LISP") has neither a function nor macro definition in ACL2. Moreover, this symbol is in the main Lisp package; hence, you cannot define it in ACL2. See :DOC near-misses. Note: this error occurred in the context (SETQ OUT (XOR (XOR A B) C)).

Can't we use main Lisp functions in ACL2? Is there another way to update variable values in ACL2? I have already tried "assign", but I don't want my variable to become global.

mnaseer
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1 Answers1

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ACL2 is an applicative programming language (in fact ACL2 stands for "A Computational Logic for Applicative Common Lisp"), so you cannot mutate values in your code; you can only bind new ones. So perhaps let or let* is what you're looking for.

kini
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