GDB history and convenience vars working

Test case:

(gdb) p 55
$1 = 55
(gdb) set $tst = $1 - 13
(gdb) p $test
$2 = void
(gdb) p $tst
$3 = 42
(gdb) p $15546
History has not yet reached $15546.
(gdb) cp $1
55
(gdb) cp $test
unknown convenience variable $test
(gdb) cp $tst
42
(gdb) cp $15546
History has not yet reached $15546.
(gdb) cp my-switch($1:$tst)
unknown convenience variable $TST
(gdb) set $TST=$tst
(gdb) cp my-switch($1:$tst)
MY-SWITCH/MY-REC(55:42)  :  ' ' <repeats 42 times>
(gdb) cp my-switch($15546:$tst)
History has not yet reached $15546.

--> all "working" / raising nice error (thinking of it again you likely want to replace those with ConditionalRaise and the appropriate Return value...