An iCalendar format lirbary.

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Yukari Hafner <shinmera@tymoon.eu>


Yukari Hafner <shinmera@tymoon.eu>



About iClendar

This is a library implementing the iCalendar file format specification according to RFC5545.

No, the name is not a typo.

How To

After loading the library, you can assemble calendar components like you would create any other class instance:

(make-instance 'iclendar:calendar
  :product "iClendar"
  :components (list (make-instance 'iclendar:event
                      :start (iclendar:make-date :year 2018 :month 8 :date 12)
                      :description "Today iClendar is released.")))

If you forget a required property, or use an invalid value, it will signal an error informing you of what's wrong. iClendar is very strict in its data constraints, which should mean that it is not possible to generate invalid data using it.

Once you have your objects assembled, you can serialise them to stream, string, or file using serialize:

(iclendar:serialize *)
;    PRODID:iClendar^M
;    VERSION:2.0^M
;    DTSTAMP:20180812T154447Z^M
;    DTSTART:20180812^M
;    UID:CCDF2E5C-D741-AD74-1F3B-A9DC01397D8D^M
;    DESCRIPTION:Today iClendar is released.^M

The Return/CR characters have been visualised as ^M here.

The iCalendar format allows you to associate metadata parameters with various properties. iClendar supports this by wrapping each property value of a component in an appropriate property instance. This instance holds both the actual value and the metadata parameters. Thus, adding metadata to a property merely requires setting the property's value, and then accessing it like so:

(iclendar:description (first (iclendar:components *)))

This will return an instance of description, one of the mentioned containers. You can now set the metadata slots on it:

(setf (iclendar:language *) "DE")

Once this is done, the serialisation will include the metadata parameter in its output:

(iclendar:serialize ***)
;    PRODID:iClendar^M
;    VERSION:2.0^M
;    DTSTAMP:20180812T161148Z^M
;    DTSTART:20180812^M
;    UID:EA6DA4AE-DAC4-ADAC-8807-1969E0E0D4AD^M
;    DESCRIPTION;LANGUAGE="DE":Today iClendar is released.^M

Parameters are, just like property values, strictly type checked.

A special note must be made for properties that contain multiple values. In that case, the slot on the component will return a list of property instances. Pushing to that slot, or setting its value in any way, will automatically ensure that it contains a list of the appropriate property instances. For example, you can easily add comments like this:

(push "Ha ha what a story, Mark" (iclendar:comments (first (iclendar:components *))))

You can also remove multiple-value property values in the same way you would handle a list. Properties that are not multiple-value can be unset as normal by using slot-makunbound.

Parsing iCalendar

Currently iClendar does not support parsing ics files.

Extension / Internal Organisation


Each of the following classes is a subclass of serializable-class, which merely keeps an identifier class slot that corresponds to the iCalendar format's identifier. For instance, the calendar's identifier is VCALENDAR.


Parameters are modelled as subclasses of a parameter-direct-slot class and thus describe custom slot types. These slot types are then used in property definitions, where they ensure that the parameter metadata has the correct type. You can define new parameters using define-parameter, or by simply individually adding them to the x-parameters slot on a property instance.


Properties are modelled as classes that have a value slot, and a slot for each of the supported parameters. They also contain a slot called x-parameters with a table for custom, non-standard parameters. You can define new property types with define-property, which takes :type and :parameters extra options to define that behaviour.

You can get an alist of all parameters of a property using parameters.


A component contains a number of properties, potential sub-components, and a slot called x-properties for extraneous, non-standard properties. Each property is modelled as a slot that maintains relational constraints of the property within the component. You can define additional components with define-component. A slot in a component definition is turned into a property-slot if the initarg :property is present. If it is, the initarg's value must be the name of a property subclass. A property-slot also takes the :constraint initarg, which describes whether it is :required, :optional, or :multiple value. The constraint may also be one of (not NAME) or (and NAME) if the property may not be or must be set alongside another.

You can get a list of all properties of a component using properties.


Serialisation of components, properties, and their types is handled by the generic function serialize-object. The stream that is passed to it should automatically ensure the proper line-folding behaviour iCalendar expects, and make sure terpri calls produce the proper CRLF output. When writing to this stream, Returns are ignored, and Linefeeds are turned into "content new lines", meaning the literal characters \ and n.

When writing textual values to the stream, you should output the string using serialize-object as well, so that it can properly escape backslashes, semi-colons, and commas.

Typically, if you merely create new parameters, properties, and components, you will not need to touch any of these functions as the standard behaviour is generic enough to cover your bases. However, if you add a new value type, you will most definitely need to add an appropriate serialize-object method for it.

Dependencies (4)

  • cl-base64
  • closer-mop
  • documentation-utils
  • trivial-gray-streams

Dependents (0)

    • GitHub
    • Quicklisp