perl -MO=Deparse -e '%a=("a",1,"b",2); print "ok" if exists $a{a} && 1+exists $a{b}'
# (%a) = ('a', 1, 'b', 2);
# print 'ok' if exists $a{'a'} and 1 + exists($a{'b'});
# NOTE above interesting and _misleading_ choice of parens, _plus_ translation to 'and'

perl -MO=Deparse -e '%a=("a",1,"b",2); print "ok" if exists($a{a} && 1+exists $a{b})'
# exists argument is not a HASH or ARRAY element at -e line 1.
# NOTE same error of course w/o Deparse, also when I move ')' behind '1'.

##</code><code>##

perl -MO=Deparse -e 'sub f {warn join "\n",@_,"",""};%a=("a",1,"b",2); print "ok" if f $a{a} && 5+f $a{b}'
# print 'ok' if f $a{'a'} && 5 + f($a{'b'});
# output 2 6 (* with sub f ($), it's 1 2)

perl -MO=Deparse -e 'sub f {warn join "\n",@_,"",""};%a=("a",1,"b",2); print "ok" if f($a{a} && 5+f $a{b})'
# print 'ok' if f $a{'a'} && 5 + f($a{'b'});
# output 5 2

perl -MO=Deparse -e 'sub f {warn join "\n",@_,"",""};%a=("a",1,"b",2); print "ok" if f($a{a} && 5)+f $a{b}'
# print 'ok' if f($a{'a'} && 5) + f($a{'b'});

perl -e 'sub f {warn join "\n",@_,"",""};%a=("a",1,"b",2); print "ok" if f($a{a}) && 5+f($a{b})'
# output 1 2

perl -e 'sub f {warn join "\n",@_,"",""};%a=("a",1,"b",2); print "ok" if f $a{a} and 5+f $a{b}'
# output 1 2