>>570 Ruby

f = -> s {
case s
when /\A(?:0|[1-9]\d*)\z|\A(?:[1-9]\d{0,2})(?:,\d{3})*\z/
:INT
when /\A(?:0?|[1-9]\d*)\.\d+\z/
:FLOAT
else
:INVALID
end
}

%w[123 1,234 1.23 a123 12abc 1.23.435 .142857 1. 0 01 1,234,567 1234,567].each{|s|
puts '%s -> %s' % [s, f[s]]
}

# =>

123 -> INT
1,234 -> INT
1.23 -> FLOAT
a123 -> INVALID
12abc -> INVALID
1.23.435 -> INVALID
.142857 -> FLOAT
1. -> INVALID
0 -> INT
01 -> INVALID
1,234,567 -> INT
1234,567 -> INVALID