: string>number ( str -- n/f )
10 <number-parse> [ @first-char ] require-next-digit ;
+: ?string>number ( str -- n/str ? )
+ dup string>number [ nip t ] [ f ] if* ;
+
: base> ( str radix -- n/f )
<number-parse> [ @first-char-no-radix ] require-next-digit ;