If-then-else had to be invented

Re:If-then-else had to be invented by kazinator on Sunday December 13, 2020 @09:18PM (#25412796)

The historical truth is that Lisp had COND first; IF was added later. Also, LAMBDA before LET.

MacCarthy writes, in History of Lisp:

I invented conditional expressions in connection with a set of chess legal move routines I wrotein FORTRAN for the IBM704 at M.I.T. during1957-58. This program did not use list processing. The IF statement provided in FORTRAN1 and FORTRAN2 was very awkward to use, and it was natural to invent a function XIF(M, N1, N2) whose value was N1 or N2 according to whether the expression M was zero or not.

Yet, no such thing was added to Lisp, initially. The 1960 Lisp 1 Programmer's Manual only lists COND.

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Re:If-then-else had to be invented by samatman on Monday December 14, 2020 @04:55PM (#25423915)

An interesting historical note, but it says nothing about the relative 'primitiveness' of COND vs IF.

It's not uncommon at all in mathematics to build a system with certain axioms, and then improve them later, when it's realized that simpler axioms can be used to build more complex constructs.

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Re:If-then-else had to be invented by kazinator on Monday December 14, 2020 @11:24PM (#25426986)

Either one of cond and if can be primitive and the other one a macro.

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