bug#21701: Fwd: cl-typecase broken (was 25.0.50; ert explainer for equal can't handle negative numbers)

[Stefan Monnier <monnier@iro.umontreal.ca>]

> However, "(format "%c" (+ (max-char) 1))" raises the error

> The question is if `cl-typecase', `format', and `characterp' should have
> the same definition on what a character is.

characterp corresponds to `base-char', at least if we want cl-*
functions to follow the Common-Lisp semantics.

> If not, then ERT must be modified to handle this, e.g. by using
> `base-char' rather than `character'.

That's indeed what should be done if ERT needs this to be a plain
character that can inserted in a string.  Common-Lisp's `character'
includes not just characters but also "characters with modifiers" such
as ?\M-\H-é, which can't appear in a string and are rejected by
`characterp'.


        Stefan