Perl does parse the string, in the case of double quotes. (Actually, it has to parse every constant string in the program to find the closing quote, but that's not precisely what you meant):

$ perl -MO=Concise
my $foo = 'bar';
my $baz = "foo${foo}bar\n";

e  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -:1) v ->3
5     <2> sassign vKS/2 ->6
3        <$> const[PV "bar"] s ->4
4        <0> padsv[$foo:1,3] sRM*/LVINTRO ->5
6     <;> nextstate(main 2 -:2) v ->7
d     <2> sassign vKS/2 ->e
-        <1> ex-stringify sK/1 ->c
-           <0> ex-pushmark s ->7
b           <2> concat[t4] sKS/2 ->c
9              <2> concat[t3] sK/2 ->a
7                 <$> const[PV "foo"] s ->8
8                 <0> padsv[$foo:1,3] s ->9
a              <$> const[PV "bar\n"] s ->b
c        <0> padsv[$baz:2,3] sRM*/LVINTRO ->d
- syntax OK
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