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MIT Scheme provides a record abstraction, which is a simple and
flexible mechanism for building structures with named components.
Records can be defined and accessed using the procedures defined in this
section. A less flexible but more concise way to manipulate records is
to use the define-structure special form (see section Structure Definitions).
procedure+: make-record-type type-name field-names
Returns a record-type descriptor, a value representing a new data type, disjoint from all others. The type-name argument must be a string, but is only used for debugging purposes (such as the printed representation of a record of the new type). The field-names argument is a list of symbols naming the fields of a record of the new type. It is an error if the list contains any duplicates. It is unspecified how record-type descriptors are represented.
procedure+: record-constructor record-type [field-names]
Returns a procedure for constructing new members of the type represented
by record-type. The returned procedure accepts exactly as many
arguments as there are symbols in the given list, field-names;
these are used, in order, as the initial values of those fields in a new
record, which is returned by the constructor procedure. The values of
any fields not named in the list of field-names are unspecified.
The field-names argument defaults to the list of field-names in
the call to make-record-type that created the type represented by
record-type; if the field-names argument is provided, it is
an error if it contains any duplicates or any symbols not in the default
list.
procedure+: record-predicate record-type
Returns a procedure for testing membership in the type represented by
record-type. The returned procedure accepts exactly one argument
and returns #t if the argument is a member of the indicated
record type; it returns #f otherwise.
procedure+: record-accessor record-type field-name
Returns a procedure for reading the value of a particular field of a
member of the type represented by record-type. 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. The symbol field-name
must be a member of the list of field names in the call to
make-record-type that created the type represented by
record-type.
procedure+: record-modifier record-type field-name
Returns a procedure for writing the value of a particular field of a
member of the type represented by record-type. 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 must be a member of the list
of field names in the call to make-record-type that created the
type represented by record-type.
For compatibility with old code, record-updater is a synonym for
this procedure.
Returns #t if object is a record of any type and #f
otherwise. Note that record? may be true of any Scheme value; of
course, if it returns #t for some particular value, then
record-type-descriptor is applicable to that value and returns an
appropriate descriptor.
procedure+: record-type-descriptor record
Returns the record-type descriptor representing the type of
record. That is, for example, if the returned descriptor were
passed to record-predicate, the resulting predicate would return
#t when passed 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 record.
procedure+: record-type? object
Returns #t if object is a record-type descriptor; otherwise
returns #f.
procedure+: record-type-name record-type
Returns the type name associated with the type represented by
record-type. The returned value is eqv? to the
type-name argument given in the call to make-record-type
that created the type represented by record-type.
procedure+: record-type-field-names record-type
Returns a list of the symbols naming the fields in members of the type
represented by record-type. The returned value is equal?
to the field-names argument given in the call to
make-record-type that created the type represented by
record-type.(13)
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