2.28.4 Terminology and conventions.

A compare procedure is a Scheme–procedure of two arguments returning an exact integer in {-1, 0, +1} such that the valid input values are ordered according to some total order. A compare procedure, together with a set of Scheme values to which it is applicable, represents a compare function.

A comparison is either an expression applying a compare procedure to two values, or the result of such an expression.

Each operation (macro or procedure) processing the value of a comparison checks if the value is indeed an exact integer in the set {-1, 0, +1}. If this is not the case, an error is signalled.

Compare procedures expecting certain types of argument should raise an error in case the arguments are not of this type. For most compare procedures specified in this SRFI, this behavior is required. A compare procedure compare can be used for type-checking value x by evaluating (compare x x), in case that is desired. This is useful in procedures like chain<? which guarantee to check each argument unconditionally.