bug#19670: 24.4; pcase-let bug?

[Stefan Monnier]

> It seems to make more sense for pcase-let to signal an error or bind X
> to nil. WDYT?

Signaling an error would be fine.  But it significantly increases the
macro-expanded code size (i.e. it's a lot less efficient).
Defaulting to binding all vars to nil in case of match failure seems
like an even more surprising behavior than what we have now.

The current pcase-let (and pcase-dolist) is meant as a "destructuring"
operation: it doesn't *check* anything, it just accesses subelements of
a structure.


        Stefan