Module Float.Class
Excluding nan the floating-point "number line" looks like:
             t                Class.t    example
           ^ neg_infinity     Infinite   neg_infinity
           | neg normals      Normal     -3.14
           | neg subnormals   Subnormal  -.2. ** -1023.
           | (-/+) zero       Zero       0.
           | pos subnormals   Subnormal  2. ** -1023.
           | pos normals      Normal     3.14
           v infinity         Infinite   infinity