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3-LISP WORKING GUIDE#2: Comparisons

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Issue #2:Arithmetic comparison primitive

Description:3-LISP doesn’t currently provide any easy way of determining the relative magnitudes of numbers.

Status:Unresolved

Last Edited:September 16, 1982 (Jim des Rivières)

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A simple fix would be to add a "less than" primitive, LT. Other kernel procedures can be defined in terms of this one. For example,

(define LE (lambda simple [n m] (or (lt n m) (= n m))))

(define GT (lambda simple [n m] (lt m n)))

(define GE (lambda simple [n m] (le m n)))

(define NEGATIVE (lambda simple [n] (lt n 0)))

It is a little unfortunate that we can’t use "<", ">", "<=", and ">=" to go along with "="; however, "<" and ">" are reserved for notating closures and the like.

It would also be feasible to choose NEGATIVE as the primitive and to define LT, LE, etc. in terms of it:

(define LT (lambda simple [n m] (negative (- n m))))