The Schemes were tested to see what happens when force is applied to a non-promise:
force returns its argument: Racket, Gauche, Gambit, Chicken, Kawa, NexJ, STklos, TinyScheme, RScheme, XLisp, UMB, Oaklisp, SXM
force signals an error: MIT, Bigloo, Scheme48/scsh, Guile, SISC, Chibi, SCM, Chez, Vicare, Larceny, Ypsilon, Mosh, IronScheme, SigScheme, Scheme 9, Dream, BDC, Schemik, Elk, VX, Sizzle, Spark, Inlab, Owl Lisp, Sagittarius
force does not exist: KSi, Shoe, S7, Rep, Llava, FemtoLisp, Dfsch
See also: Disjoint promises.