Hi

I am at ELS 2024 in Vienna and I saw Andrea Corallo's presentation about
the introduction of the

(defun foo (x)
    *(declare (type (function (integer) float))*
    (+ x 42.0))

declaration.

IMHO (and, I am not afraid to say, of many common lispers) this is
shortsighted and a rather gratuitous departure from what CL does.  With
some potential unintended consequences down the road.

The declaration proposed is for the *signature* of the function as a
whole.  Using type may prevent ELisp from introducing the usual CL idiom,
as the following one

(let ((x 42) (y -1))
    *(declare (type integer x y))* ; The type declaration refers to names x
and y.
...)

... unless you special case the type declaration with no name(s) following
the type spec.

My suggestion: keep type (and ftype) for doing things the CL way (which was
the PL/I way :) ) and introduce a signature spec to be meaningful only at
the function toplevel.

(defun foo (x)
    *(declare (signature (function (integer) float))*
    (+ x 42.0))

All the best
-- 
Marco Antoniotti, Professor                   tel. +39 - 02 64 48 79 01
DISCo, University of Milan-Bicocca U14 2043   http://dcb.disco.unimib.it
Viale Sarca 336
I-20126 Milan (MI) ITALY