opposite of chr(int)

Looking at the string functions on:
http://www.postgresql.org/docs/9.0/static/functions-string.html

I only see chr(int) and not something like int(chr).

reading through the others on that page i do not see a int(chr)

the goal is to tell whether or not a character in a string is an integer or
not

my current workaround is this:

select
case
when substring('wallawa9kl',8,1) = '0' then 'true'
when substring('wallawa9kl',8,1) = '1' then 'true'
when substring('wallawa9kl',8,1) = '2' then 'true'
when substring('wallawa9kl',8,1) = '3' then 'true'
when substring('wallawa9kl',8,1) = '4' then 'true'
when substring('wallawa9kl',8,1) = '5' then 'true'
when substring('wallawa9kl',8,1) = '6' then 'true'
when substring('wallawa9kl',8,1) = '7' then 'true'
when substring('wallawa9kl',8,1) = '8' then 'true'
when substring('wallawa9kl',8,1) = '9' then 'true'
else 'false'
end

just wondering if there is something more compact or if this is an okay
workaround solution.