isnumeric(varchar) by psql

Hello,

Does psql provide a function isnumeric(varchar) to check if a varchar 
can be converted to a numeric field?

E.g.,    x     | isnumeric
----------+-----------          | f .        | f .0       | t 0.       | t 0        | t 1        | t 123      | t
123.456 | t abc      | f 1..2     | f 1.2.3.4  | f 1x234    | f 1.234e-5 | t
 

Thanks a lot
Emi
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Found examples users created by self. If psql provides similar one already?