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Comment by lispm | Hacker News Reader

for a specific expression on can also specify the return type using THE:

    (the fixnum (+ a b))

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That’s a hilarious but perfect piece of syntax. Do you know where it originated?

Per: https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node106.html

> Compatibility note: This construct is borrowed from the Interlisp DECL package; Interlisp, however, allows an implicit progn after the type specifier rather than just a single form. The MacLisp fixnum-identity and flonum-identity constructs can be expressed as (the fixnum x) and (the single-float x).

agreed^^ there are macros and libraries to bring a nicer syntax (of course). Exple: https://github.com/lisp-maintainers/defstar

   (defun* (sum -> real) ((a real) (b real))
       (+ a b))

There is DECLARE, PROCLAIM, and DECLAIM. I always interpreted the latter to be a portmanteau of the former two.

Right, though I'm not sure it's easy to infer an ordinary function's return type from this kind of declaration.

Speaking of return types, do you have any idea if any implementation takes a generic function's return type declaration seriously? I believe SBCL currently doesn't, which is unfortunate (defmethods keep clobbering the ftype declaration).

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