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6.6.17 Records

   A record type is a first class object representing a user-defined data type. A
   record is an instance of a record type.

   Note that in many ways, this interface is too low-level for every-day use. Most
   uses of records are better served by SRFI-9 records. See [12]SRFI-9 Records.

   Scheme Procedure: record? obj[13] ¶
          Return #t if obj is a record of any type and #f otherwise.

          Note that record? may be true of any Scheme value; there is no promise
          that records are disjoint with other Scheme types.

   Scheme Procedure: make-record-type type-name field-names [print] [#:parent=#f]
          [#:uid=#f] [#:extensible?=#f] [#:opaque?=#f]
          [#:allow-duplicate-field-names?=#t][14] ¶
          Create and return a new record-type descriptor.

          type-name is a string naming the type. Currently it's only used in the
          printed representation of records, and in diagnostics. field-names is a
          list of elements of the form (immutable name), (mutable name), or name,
          where name are symbols naming the fields of a record of the type.
          Duplicates are not allowed among these symbols, unless
          allow-duplicate-field-names? is true.

(make-record-type "employee" '(name age salary))

          The optional print argument is a function used by display, write, etc, for
          printing a record of the new type. It's called as (print record port) and
          should look at record and write to port.

          Pass the #:parent keyword to derive a record type from a supertype. A
          derived record type has the fields from its parent type, followed by
          fields declared in the make-record-type call. Record predicates and field
          accessors for instance of a parent type will also work on any instance of
          a subtype.

          Allowing record subtyping has a small amount of overhead. To avoid this
          overhead, prevent extensibility by passing #:extensible? #f. By default,
          record types in Guile are not extensible.

          Generally speaking, calling make-record-type returns a fresh record type;
          it generates new record types. However sometimes you only want to define a
          record type if one hasn't been defined already. For a nongenerative record
          type definition, pass a symbol as the #:uid keyword parameter. If a record
          with the given uid was already defined, it will be returned instead. The
          type name, fields, parent (if any), and so on for the previously-defined
          type must be compatible.

          R6RS defines a notion of "opaque" record types. Given an instance of an
          opaque record type, one cannot obtain a run-time representation of the
          record type. See [15]rnrs records procedural, for full details. The
          #:opaque? flag is used by Guile's R6RS layer to record this information.
          The default is determined by whether the parent type, if any, was opaque.

          Fields are mutable by default, meaning that record-modifier will return a
          procedure that can update a record in place. Specifying a field using the
          form (immutable name) instead marks a field as immutable.

   Scheme Procedure: record-constructor rtd[16] ¶
          Return a procedure for constructing new members of the type represented by
          rtd. The result will be a procedure accepting exactly as many arguments as
          there are fields in the record type.

   Scheme Procedure: record-predicate rtd[17] ¶
          Return a procedure for testing membership in the type represented by rtd.
          The returned procedure accepts exactly one argument and returns a true
          value if the argument is a member of the indicated record type; it returns
          a false value otherwise.

   Scheme Procedure: record-accessor rtd field-name[18] ¶
          Return a procedure for reading the value of a particular field of a member
          of the type represented by rtd. The returned procedure accepts exactly one
          argument which must be a record of the appropriate type; it returns the
          current value of the field named by the symbol field-name in that record.

          If field-name is a symbol, it must be a member of the list of field-names
          in the call to make-record-type that created the type represented by rtd.
          If multiple fields in rtd have the same name, record-accessor returns the
          first one.

          If field-name is an integer, it should be an index into
          (record-type-fields rtd). This allows accessing fields with duplicate
          names.

   Scheme Procedure: record-modifier rtd field-name[19] ¶
          Return a procedure for writing the value of a particular field of a member
          of the type represented by rtd. The returned procedure accepts exactly two
          arguments: first, a record of the appropriate type, and second, an
          arbitrary Scheme value; it modifies the field named by the symbol
          field-name in that record to contain the given value. The returned value
          of the modifier procedure is unspecified. The symbol field-name is a field
          name or a field index, as in record-modifier.

   Scheme Procedure: record-type-descriptor record[20] ¶
          Return a record-type descriptor representing the type of the given record.
          That is, for example, if the returned descriptor were passed to
          record-predicate, the resulting predicate would return a true value when
          passed the given record. Note that it is not necessarily the case that the
          returned descriptor is the one that was passed to record-constructor in
          the call that created the constructor procedure that created the given
          record.

   Scheme Procedure: record-type-name rtd[21] ¶
          Return the type-name associated with the type represented by rtd. The
          returned value is eqv? to the type-name argument given in the call to
          make-record-type that created the type represented by rtd.

   Scheme Procedure: record-type-fields rtd[22] ¶
          Return a list of the symbols naming the fields in members of the type
          represented by rtd. The returned value is equal? to the field-names
          argument given in the call to make-record-type that created the type
          represented by rtd.
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References

   1. http://www.gnu.org/software/guile/manual/html_node/index.html
   2. http://www.gnu.org/software/guile/manual/html_node/Concept-Index.html
   3. http://www.gnu.org/software/guile/manual/html_node/index.html#SEC_Contents
   4. http://www.gnu.org/software/guile/manual/html_node/Data-Types.html
   5. http://www.gnu.org/software/guile/manual/html_node/Structures.html
   6. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d9-Records.html
   7. http://www.gnu.org/software/guile/manual/html_node/Structures.html
   8. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d9-Records.html
   9. http://www.gnu.org/software/guile/manual/html_node/Data-Types.html
  10. http://www.gnu.org/software/guile/manual/html_node/index.html#SEC_Contents
  11. http://www.gnu.org/software/guile/manual/html_node/Concept-Index.html
  12. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d9-Records.html
  13. http://www.gnu.org/software/guile/manual/html_node/Records.html#index-record_003f
  14. http://www.gnu.org/software/guile/manual/html_node/Records.html#index-make_002drecord_002dtype
  15. http://www.gnu.org/software/guile/manual/html_node/rnrs-records-procedural.html
  16. http://www.gnu.org/software/guile/manual/html_node/Records.html#index-record_002dconstructor
  17. http://www.gnu.org/software/guile/manual/html_node/Records.html#index-record_002dpredicate
  18. http://www.gnu.org/software/guile/manual/html_node/Records.html#index-record_002daccessor
  19. http://www.gnu.org/software/guile/manual/html_node/Records.html#index-record_002dmodifier
  20. http://www.gnu.org/software/guile/manual/html_node/Records.html#index-record_002dtype_002ddescriptor
  21. http://www.gnu.org/software/guile/manual/html_node/Records.html#index-record_002dtype_002dname
  22. http://www.gnu.org/software/guile/manual/html_node/Records.html#index-record_002dtype_002dfields
  23. http://www.gnu.org/software/guile/manual/html_node/Structures.html
  24. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d9-Records.html
  25. http://www.gnu.org/software/guile/manual/html_node/Data-Types.html
  26. http://www.gnu.org/software/guile/manual/html_node/index.html#SEC_Contents
  27. http://www.gnu.org/software/guile/manual/html_node/Concept-Index.html