imagpart - a real.

complex - a rational or a complex.

If realpart is a rational and imagpart is the rational number zero, the result of complex is realpart, a rational. Otherwise, the result is a complex.

If either realpart or imagpart is a float, the non-float is converted to a float before the complex is created. If imagpart is not supplied, the imaginary part is a zero of the same type as realpart; i.e., (coerce 0 (type-of realpart)) is effectively used.

Type upgrading implies a movement upwards in the type hierarchy lattice. In the case of complexes, the type-specifier must be a subtype of (upgraded-complex-part-type type-specifier). If type-specifier1 is a subtype of type-specifier2, then (upgraded-complex-element-type 'type-specifier1) must also be a subtype of (upgraded-complex-element-type 'type-specifier2). Two disjoint types can be upgraded into the same thing.

 (complex 0)  0
 (complex 0.0)  #C(0.0 0.0)
 (complex 1 1/2)  #C(1 1/2)
 (complex 1 .99)  #C(1.0 0.99)
 (complex 3/2 0.0)  #C(1.5 0.0)