diff options
| -rw-r--r-- | guix/records.scm | 33 |
1 files changed, 32 insertions, 1 deletions
diff --git a/guix/records.scm b/guix/records.scm index cd887b77ce..93c52f0ffa 100644 --- a/guix/records.scm +++ b/guix/records.scm @@ -46,7 +46,38 @@ (lambda (s) "Define the given record type such that an additional \"syntactic constructor\" is defined, which allows instances to be constructed with named -field initializers, à la SRFI-35, as well as default values." +field initializers, à la SRFI-35, as well as default values. An example use +may look like this: + + (define-record-type* <thing> thing make-thing + thing? + (name thing-name (default \"chbouib\")) + (port thing-port + (default (current-output-port)) (thunked))) + +This example defines a macro 'thing' that can be used to instantiate records +of this type: + + (thing + (name \"foo\") + (port (current-error-port))) + +The value of 'name' or 'port' could as well be omitted, in which case the +default value specified in the 'define-record-type*' form is used: + + (thing) + +The 'port' field is \"thunked\", meaning that calls like '(thing-port x)' will +actually compute the field's value in the current dynamic extent, which is +useful when referring to fluids in a field's value. + +It is possible to copy an object 'x' created with 'thing' like this: + + (thing (inherit x) (name \"bar\")) + +This expression returns a new object equal to 'x' except for its 'name' +field." + (define (make-syntactic-constructor type name ctor fields thunked defaults) "Make the syntactic constructor NAME for TYPE, that calls CTOR, and expects all of FIELDS to be initialized. DEFAULTS is the list of |