/// <summary>
/// Apply the primitive to the arguments, giving a result.
/// As a convenience for primitives, they are allowed to return either
/// a result or a Evaluator. If they return an evaluator, it means the result
/// is not yet ready, and that a new evaluator was created and returned. When
/// that evaluator has a result, it will put in into ReturnedResult and return to the
/// caller evaluator provided to it.
/// If there is a result available immediately, this returns it by storing it
/// in ReturnedResult and returning to the caller.
/// </summary>
/// <param name="args">The arguments to the primitive.</param>
/// <param name="env">The application environment.</param>
/// <param name="returnTo">The evaluator to return to. This can be different from caller if this is the last step in evaluation</param>
/// <param name="caller">The calling Evaluator.</param>
/// <returns>The next evaluator to execute.</returns>
internal override Evaluator Apply(SchemeObject args, Environment env, Evaluator returnTo, Evaluator caller)
{
// First check the number of arguments
#if Check
this.CheckArgTypes(args, caller);
#endif
#if Diagnostics
returnTo.IncrementCounter(this + ":apply");
#endif
// Execute the operation
var res = this.operation(args, env, returnTo);
// See if the operation returns a result or another evaluator
var evaluator = res as Evaluator;
if (evaluator != null)
{
return evaluator;
}
// Operation returned a result -- just return this
// to the caller.
returnTo.ReturnedExpr = (SchemeObject)res;
return returnTo;
}
