complex realpart &optional imagpart => complex
complex---a rational or a complex.
complex returns a number whose real part is realpart and whose imaginary part is imagpart.
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)