How a variety of Schemes represent complex numbers:
Exact, inexact, and mixed complex number representations, where inexact and mixed numbers that are = are nevertheless distinct in the sense of eqv?: Gambit, Chibi. (Also CLISP, Pure.)
Exact, inexact, and mixed complex number representations, where inexact and mixed numbers that are = are the same in the sense of eqv?: MIT, STklos.
Exact and inexact complex number representations only (mixed complex numbers become inexact): Racket, Chicken with the numbers egg, Scheme48/scsh, Kawa, Chez, Vicare, Larceny, Ypsilon, IronScheme, Spark, Wraith. (Also ABCL, Allegro CL, Clozure CL, CMUCL, ECL, GNU CL, LispWorks, SBCL, Scieneer CL.)
Inexact complex number representations only: Gauche, Guile, SISC, SCM, KSi, Scheme 7, UMB, Stalin. (Also Fortran, C/C++, Python, etc.)
Exact complex number representations only: Owl Lisp (which has no inexact numbers).
No complex numbers: plain Chicken, Bigloo, Ikarus, NexJ, SigScheme, Shoe, TinyScheme, Scheme 9, Dream, RScheme, BDC, XLisp, Rep, Schemik, Elk, VX, Oaklisp, Llava, SXM, Sizzle, FemtoLisp, Dfsch, Inlab.
Mosh has a bug whereby numbers that are = are always eqv? even if they differ in exactness; it supports exact, inexact, and mixed complex number representations, but doesn't differentiate exact from inexact properly.
See also NumericTower.