Bigloo supports two kinds of enumerated types: the
structures and
the
records. They offer similar facilities. Structures were
pre-existing to records and they are maintained mainly for backward
compatiblity. Recors are compliant with the Scheme request for
implementation 9.
There is, in Bigloo, a new class of objects:
structures, which are equivalent to C
struct.
| define-struct name field... | bigloo syntax |
This form defines a structure with name name, which is a symbol,
having fields field... which are symbols or lists, each
list being composed of a symbol and a default value. This form creates
several functions: creator, predicate, accessor and assigner functions. The
name of each function is built in the following way:
- Creator:
make-name
- Predicate:
name?
- Accessor:
name-field
- Assigner:
name-field-set!
Function make-name accepts an optional argument. If
provided, all the slots of the created structures are filled with it. The
creator named name accepts as many arguments as the number of
slots of the structure. This function allocates a structure and fills
each of its slots with its corresponding argument.
If a structure is created using make-name and no initialization
value is provided, the slot default values (when provided) are used
to initialize the new structure. For instance, the execution of the program:
(define-struct pt1 a b)
(define-struct pt2 (h 4) (g 6))
(make-pt1)
=> #{PT1 () ()}
(make-pt1 5)
=> #{PT1 5 5}
(make-pt2)
=> #{PT2 4 6}
(make-pt2 5)
=> #{PT2 5 5}
|
|
| struct? obj | bigloo procedure |
Returns #t if and only if obj is a structure.
|
Bigloo supports records has specified by SRFI-9. This section is a copy
of the SRFI-9 specification by Richard Kelsey. This SRFI describes
syntax for creating new data types, called record types. A predicate,
constructor, and field accessors and modifiers are defined for each
record type. Each new record type is distinct from all existing types,
including other record types and Scheme's predefined types.
| define-record-type expression... | syntax |
The syntax of a record-type definition is:
<record-type-definition> ==> (define-record-type <type-name>
(<constructor-name> <field-tag> ...)
<predicate-name>
<field-spec> ...)
<field-spec> ==> (<field-tag> <accessor-name>)
| (<field-tag> <accessor-name> <modifier-name>)
<field-tag> ==> <identifier>
<accessor-name> ==> <identifier>
<predicate-name> ==> <identifier>
<modifier-name> ==> <identifier>
<type-name> ==> <identifier>
|
Define-record-type is generative: each use creates a new record
type that is distinct from all existing types, including other record
types and Scheme's predefined types. Record-type definitions may only
occur at top-level (there are two possible semantics for `internal'
record-type definitions, generative and nongenerative, and no consensus
as to which is better).
an instance of define-record-type is equivalent to the following
definitions:
<type-name>
is bound to a representation of the record type itself. Operations on
record types, such as defining print methods, reflection, etc. are left
to other SRFIs.
<constructor-name>
is bound to a procedure that takes as many arguments as the
re are <field-tag>s in the (<constructor-name> ...) subform
and returns a new <type-name> record. Fields whose tags are listed
with <constructor-name> have the corresponding argument as their
initial value. The initial values of all other fields are unspecified.
<predicate-name>
is a predicate that returns #t when given a value returned by
<constructor-name> and #f for everything else.
- Each
<accessor-name> is a procedure that takes a record of
type <type-name> and returns the current value of the corresponding
field. It is an error to pass an accessor a value which is not a record
of the appropriate type.
- Each
<modifier-name> is a procedure that takes a record of
type <type-name> and a value which becomes the new value of the
corresponding field; an unspecified value is returned. It is an error
to pass a modifier a first argument which is not a record of the appropriate
type.
Records are disjoint from the types listed in Section 4.2 of R5RS.
Seting the value of any of these identifiers has no effect on the
behavior of any of their original values.
The following
(define-record-type pare
(kons x y)
pare?
(x kar set-kar!)
(y kdr))
|
defines kons to be a constructor, kar and kdr to be
accessors, set-kar! to be a modifier, and pare? to be a
predicate for pares.
(pare? (kons 1 2)) => #t
(pare? (cons 1 2)) => #f
(kar (kons 1 2)) => 1
(kdr (kons 1 2)) => 2
(let ((k (kons 1 2)))
(set-kar! k 3)
(kar k)) => 3
|
|