use constant FOOBAR => "a" x 3;

##</code><code>##

BEGIN { my $x = "a" x 3; *::FOOBAR = sub () { $x } }

##</code><code>##

$ perl -MO=Concise,BEGIN,-main -e'use constant FOOBAR => "a" x 3; print FOOBAR' | grep -C 3 '"a'
14             <$> const[PV "constant"] sM ->15
15             <$> const[PV "FOOBAR"] sM/BARE ->16
18             <2> repeat[t1] sKM/2 ->19                  # <---
16                <$> const[PV "a"] s ->17                # <---
17                <$> const[IV 3] s ->18                  # <---
19             <$> method_named[PV "import"] ->1a
BEGIN 5:
-e syntax OK
--
4i    <;> nextstate(main 102 -e:1) v:{ ->4j
4l    <@> print vK ->4m
4j       <0> pushmark s ->4k
4k       <$> const[PV "aaa"] s ->4l


##</code><code>##

$ perl -MO=Concise -e'use constant FOOBAR => scalar <STDIN>; print FOOBAR'
abc
6  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 102 -e:1) v:{ ->3
5     <@> print vK ->6
3        <0> pushmark s ->4
4        <$> const[PV "abc\n"] s ->5     # <---