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make-parameter VALUE #!optional GUARDprocedure

Returns a procedure that accepts zero or one argument. Invoking the procedure with zero arguments returns VALUE. Invoking the procedure with one argument changes its value to the value of that argument and returns the new value (subsequent invocations with zero parameters return the new value). GUARD should be a procedure of a single argument. Any new values of the parameter (even the initial value) are passed to this procedure. The guard procedure should check the value and/or convert it to an appropriate form.

This special form is compatible with the definition from the R7RS (scheme base) library.