$ perl -MO=Deparse,-p -le " $a= 1 && 2; print $a; "
BEGIN { $/ = "\n"; $\ = "\n"; }
($a = 2);
print($a);
-e syntax OK

$ perl -MO=Deparse,-p -e "  $a && $b = 3; "
Can't modify logical and (&&) in scalar assignment at -e line 1, near "3;"
-e had compilation errors.
(($a && $b) = 3);


##</code><code>##


2012         /* FALL THROUGH */
2013     default:
2014       nomod:
2015         if (flags & OP_LVALUE_NO_CROAK) return NULL;
2016         /* grep, foreach, subcalls, refgen */
2017         if (type == OP_GREPSTART || type == OP_ENTERSUB
2018          || type == OP_REFGEN    || type == OP_LEAVESUBLV)
2019             break;
2020         yyerror(Perl_form(aTHX_ "Can't modify %s in %s",
2021                      (o->op_type == OP_NULL && (o->op_flags & OPf_SPECIAL)
2022                       ? "do block"
2023                       : (o->op_type == OP_ENTERSUB
2024                         ? "non-lvalue subroutine call"
2025                         : OP_DESC(o))),
2026                      type ? PL_op_desc[type] : "local"));