From a14c9600d3838595fafe7f3fb3b99fef8492a012 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Mon, 2 Oct 2023 19:28:13 +0200
Subject: Documentation work.

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+@node YAOS Primitives
+@section Primitives
+
+What Scheme lacks is a proper object system. This library solves that
+problem @emph{once and for all}!
+
+The records created through this library are all immutale, where each
+field becomes a multiple dispatch procedure, whence called with a
+single argument returns the value of that field, and when called with
+two values (first one being the object, second being the new value)
+returns a new instance of the object, with the field in question
+replaced.
+
+@defmac define-type (name type-parameters ...) fields ...
+Introduce a new type, disjoint from all previously defined types.
+
+@c Each field is either a symbol, or a list where the first element is a
+@c symbol, and the remaining elements are alternating keywords and
+@c values, as per @ref{Field Parameters}. All fields are optional by
+@c default, but can be made non-optional through its type parameter.
+
+@c The example below creates a new type called @var{type}, with a custom
+@c printer which always displays the string ``TYPE''. It has two fields,
+@c @var{x}, which must be an integer, and @var{y}, which can have any
+@c type, but gets the value ``Hello'' in none is given.
+@c @example
+@c (define-type (type #:printer (lambda (r p) (display "TYPE" p)))
+@c   (x #:type integer?)
+@c   (y #:default "Hello"))
+@c @end example
+
+@var{type-parameters} is a key-value list, where the valid keys are
+
+@deffn {Type Parameter} #:constructor (λ (primitive-constructor type-validator))
+The defaulct constructor for these types simply takes a keyword-value
+list, validates each argument in regard to the defined types, and
+constructs a final object. However; sometimes a more advanced
+constructor is needed, which can be added through this parameter.
+
+The custom constructor is called with two values:
+
+@itemize
+@item the types primitive (and usually hidden) constructor,
+which takes as many arguments as there are fields, in the order given
+in define-type, and
+@item the type validator procedure, which also takes all arguments,
+but instead either returns an undefined value if everything is fine,
+or throws @code{'wrong-type-arg} otherwise.
+@end itemize
+The procedure should then return a new procedure, which will be bound
+as the constructor for the type. Note that default values are current
+disregarded with custom constructors.
+
+A custom constructor for the type above might look like
+@example
+(lambda (primitive-constructor type-check)
+  (lambda* (#:key x y)
+    (type-check x y)
+    (primitive-constructor x y)))
+@end example
+@end deffn
+
+@deffn {Type Parameter} #:printer (λ (record port))
+Use a custom printer for the type.
+@end deffn
+
+Each field declares a part of the record, along with relevant metadata
+about that field. The most basic declaration is a bare symbol, which
+adds a field which can hold anything. However, a list with the target
+name as its first element can instead be given, with the tail
+containing keyword arguments as follows
+
+@deffn {Field Parameter} default value
+Value the field should get if not given.
+@end deffn
+
+@deffn {Field Parameter} type type-clause
+A type predicate that the field must obey. See @ref{type-clause} for details.
+
+Each type introduces a number of bindings, which are@footnote{
+@var{<name>} here refers to the name of the type
+}:
+@end deffn
+
+@defun @var{<name>} [kv-args ...]
+Type constructor. Takes key-value arguments. Where the keys are the
+names of the fields.
+@end defun
+
+@defun @var{<name>}? x
+Type predicate.
+@end defun
+
+And for each field @var{<field>}:
+
+@defun @var{<field>} object [value]
+Accessor for the given filed.
+Returns the current value if called with only an object, and returns a
+new object with @var{field} set to @var{value} if called with two values.
+
+The updating version checks the type if #:type was given on creation.
+@end defun
+
+@end defmac
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