( Procedures with Setters

Info Catalog ( Procedure Properties ( Procedures and Macros ( Macros
 23.4 Procedures with Setters
 A "procedure with setter" is a special kind of procedure which normally
 behaves like any accessor procedure, that is a procedure which accesses
 a data structure.  The difference is that this kind of procedure has a
 so-called "setter" attached, which is a procedure for storing something
 into a data structure.
    Procedures with setters are treated specially when the procedure
 appears in the special form `set!' (REFFIXME).  How it works is best
 shown by example.
    Suppose we have a procedure called `foo-ref', which accepts two
 arguments, a value of type `foo' and an integer.  The procedure returns
 the value stored at the given index in the `foo' object.  Let `f' be a
 variable containing such a `foo' data structure.(1)
      (foo-ref f 0)       => bar
      (foo-ref f 1)       => braz
    Also suppose that a corresponding setter procedure called `foo-set!'
 does exist.
      (foo-set! f 0 'bla)
      (foo-ref f 0)       => bla
    Now we could create a new procedure called `foo', which is a
 procedure with setter, by calling `make-procedure-with-setter' with the
 accessor and setter procedures `foo-ref' and `foo-set!'.  Let us call
 this new procedure `foo'.
      (define foo (make-procedure-with-setter foo-ref foo-set!))
    `foo' can from now an be used to either read from the data structure
 stored in `f', or to write into the structure.
      (set! (foo f 0) 'dum)
      (foo f 0)          => dum
  -- Scheme Procedure: make-procedure-with-setter procedure setter
  -- C Function: scm_make_procedure_with_setter (procedure, setter)
      Create a new procedure which behaves like PROCEDURE, but with the
      associated setter SETTER.
  -- Scheme Procedure: procedure-with-setter? obj
  -- C Function: scm_procedure_with_setter_p (obj)
      Return `#t' if OBJ is a procedure with an associated setter
  -- Scheme Procedure: procedure proc
  -- C Function: scm_procedure (proc)
      Return the procedure of PROC, which must be either a procedure
      with setter, or an operator struct.
  -- Scheme Procedure: setter proc
      Return the setter of PROC, which must be either a procedure with
      setter or an operator struct.
    ---------- Footnotes ----------
    (1) Working definitions would be:
      (define foo-ref vector-ref)
      (define foo-set! vector-set!)
      (define f (make-vector 2 #f))
Info Catalog ( Procedure Properties ( Procedures and Macros ( Macros
automatically generated byinfo2html