Floating point constants have the syntax
[-]?[0-9]+(.[0-9]+)?([eE]([-]?)[0-9]+)?
where the decimal point is a literal and at least one of the fractional and exponent clauses must be present:
1.0
12.3
1e3 # 1000.0
1E-3 # 0.001
Float constants have type float64::Float.