An HTML templating engine using Plump.

About Clip

Clip is an attempt at a templating library that allows you to write templates in a way that is both accessible to direct webdesign and flexible. The main idea is to incorporate transformation commands into an HTML file through tags and attributes. Clip is heavily dependant on Plump and lQuery.

How To

Load Clip through ASDF or Quicklisp.

(ql:quickload :clip)

To process a template, simply call PROCESS:

(clip:process #p"my-template.ctml")

You may also pass in pure strings or plump nodes. Most likely you will want to include some kind of data in your template. Data in Clip is managed through a central CLIPBOARD. The additional arguments you pass to PROCESS are entered into the initial clipboard like a plist (key and value alternating).

Depending on the current tag environment and how the template is processed at the time these values can come into play. Most of the time, entering the name as passed into PROCESS in the template as an attribute value will then evaluate to the according value using RESOLVE-VALUE. In the case of a symbol this then delegates to CLIP, which returns the value stored in the clipboard.

The value returned by PROCESS is the node you passed into it. You can parse this back into a string using PLUMP:SERIALIZE or lQuery's WRITE-TO-FILE.

Standard Tags

    This tag expands its attributes and then calls PROCESS-NODE on itself again. This is useful to generate attributes to be expanded.
  • C:IF
    Looks for either a TEST attribute or a C:TEST tag as one of its direct children. If the test as by RESOLVE-VALUE is non-NIL, all children of the C:THEN tag are spliced in place of the IF block. Otherwise the same is done for the C:ELSE block. If neither C:THEN or C:ELSE blocks are found as direct children of the C:IF, the C:IF is simply removed from the DOM.
    Looks for one attribute called OVER and then works like the ITERATE attribute processor using the value of the OVER attribute.
  • C:LET
    Creates a new clipboard environment with all the tag attributes bound in the following manner: The attribute key is put into the clipboard directly and associated with the value of RESOLVE-VALUE of the attribute value. Acts like SPLICE.
  • C:NOOP
    This tag only processes its attributes, but none of its children.
    Splices all nodes within it into the parent's child list at the position of itself (essentially replacing it with its children).
    Same as WHEN, but inverted.
    Binds the clipboard to the resolved-value of its VALUE attribute. Acts like SPLICE.
  • C:WHEN
    Looks for a TEST attribute and if the value of it as by RESOLVE-VALUE is non-NIL, acts like SPLICE. Otherwise it removes itself including its children from the DOM.

If you specify attributes that are not known on a standard tag, a warning of type UNKNOWN-ATTRIBUTE is signalled. If you do not specify a required attribute on a standard tag, an error of type MISSING-ATTRIBUTE is signalled.

Standard Attributes

  • AS
    Simply changes that node's tag-name to the value of this attribute.
    Inserts the value of *TARGET-COUNT* as the attribute value. This is useful to follow processing order during debugging.
  • EVAL
    Simply calls EVAL on the value of READ-FROM-STRING of the attribute value.
    The value (as by RESOLVE-VALUE) is used as an iteration list or vector. The first node within the node this attribute belongs to is copied once for each item in the iteration list and processed with that item used as the clipboard.
    Calls lQuery functions on the node as if by ($ node ..). Note that only lQuery functions are available, not its macros.
  • FILL
    The attribute value is read as a plist, the keys of which designate other attribute names and the values are resolved to the objects to use. For each named attribute, its value is modified by replacing {thing} by the result of clip on the respective object's field thing.

Extending Clip

You can define new tag and attribute processors with the macros DEFINE-TAG-PROCESSOR and DEFINE-ATTRIBUTE-PROCESSOR. For tag processors you will usually want to make sure to call PROCESS-ATTRIBUTES and PROCESS-CHILDREN to ensure that tags and attributes within are properly processed. To retrieve values most of the time you need to use RESOLVE-VALUE (or its shorthand RESOLVE-ATTRIBUTE) unless you want to whip up your own system for one reason or another. All tags that you define will automatically be prefixed with C: in order to help highlighting template tags and ensure that there are no collisions with existing tags.

Editor Support

The Emacs extension Web-Mode(version 9.0.77+) provides syntax highlighting for Clip templates. In order for it to recognise the templates, use the .ctml file extension. A huge thanks goes to Bois Francois-Xavier for adding the support.


These are short tutorials to help explaining the effects of each tag and to illustrate some basic templating techniques. The examples will only work with Clip>=0.5.1 and lQuery>=3.1.1 .

Updating a node with values

 "<span lquery=\"(text text) (add-class class)\" />"
 :text "Hi!" :class "clip-text")

Explanation: The LQUERY attribute allows you to perform lQuery operations on the node it is an attribute of. In this case, the TEXT function sets the text of the node to the value of TEXT, which we told Clip to be "Hi!". Similarly for ADD-CLASS. Any non-keyword symbol within the template is automatically resolved to a field on the current clipboard. You may think of the clipboard as a form of lexical environment for the template, which we currently set to have the variables TEXT and CLASS bound. The default CLIPBOARD object is special in the sense that it does not differentiate between accessing it with keywords, symbols or strings and is case-insensitive. This makes it easier to access in templates.

Please see the lQuery documentation for all possible node manipulation functions.

Populating from a list

 "<ol iterate=\"todo-list\"><li lquery=\"(text *)\"></li></ol>"
 :todo-list '("Write tutorials" "Make tiramisu" "Visit grandma"))

The ITERATE attribute goes over the list or vector of elements its attribute-value resolves to and uses each item as the current clipboard for the iteration element. Since in this case these values themselves are direct strings we cannot retrieve further values from them and instead need to use * to refer to the entire clipboard.


 "<ul iterate=\"users\">
  <li><c:if test=\"anonymous\"><c:then>Username Hidden</c:then><c:else lquery=\"(text username)\"/></c:if></li>
 :users '((:username "Some Guy" :anonymous T) (:username "Some Other Guy" :anonymous NIL) (:username "You" :anonymous NIL)))

Clip offers a couple of constructs to perform conditionals. These constructs are C:WHEN C:UNLESS and C:IF, after their CL equivalents. Each take an attribute called TEST that has to resolve to a non-NIL value to be taken as true. In the case of C:IF, three special local child tags are used: C:THEN, C:ELSE and C:TEST. The C:TEST tag can be used as an alternative to the test attribute. The other two should be self-explanatory. Note that none of the child-tags or attributes of an unchosen branch are processed.


 "<c:using value=\"num\">
  <c:let orig=\"*\" double=\"(* * 2)\" square=\"(expt * 2)\" root=\"(sqrt *)\">
    <span lquery=\"(text (list orig double square root))\" />
 :num 2)

In order to manipulate the clipboard bindings you can use the C:USING and C:LET special tags. C:USING replaces the clipboard environment with what the value of its VALUE attribute resolves to. C:LET on the other hand creates a new CLIPBOARD object, setting the specified symbol/value pairs from its attributes.

Clipboard Stack

 "<ul iterate=\"articles\">
    <header><div class=\"author\" lquery=\"(text (** :author))\">AUTHOR</div></header>
    <section class=\"content\" lquery=\"(text *)\">CONTENT</section>
 :author "Max Mastermind" :articles '("Whoa I am blogging!!" "I don't know what to write, sadface."))

Sometimes you need to refer to values in clipboards outside of the current binding. No worries, this is easy to do as the clipboards are organised using a stack. You can reach clipboards higher up in the stack using the asterisk symbols. Each asterisk more is one clipboard higher. Using the asterisk symbol as a variable returns the clipboard directly, using it as a function call is akin to doing (CLIP ** 'thing). In order to avoid clashing with the * multiplication function, the asterisk function shorthand is only active for two or more asterisks.

Function References

(defun seconds () (decode-universal-time (get-universal-time)))
 "<time lquery=\"(text (seconds))\">TIME</time>")

Whenever you require to use functions within clip documents, you need to be aware of the current value of *package*. As values that are resolved are first parsed using read, they are influenced by *package*. You can of course use fully qualified symbol names, but often times it is useful to bind the variable to the package you need to reduce verbosity.

You must also be aware of the special resolving for symbols used as function calls within standard resolvings. As mentioned in the previous section, symbols only consisting of asterisks are specially handled. Additionally, the symbols cl:quote, cl:function, cl:or, cl:and, cl:if, cl:when, and cl:unless are handled to work like their usual macro/special equivalents. Any other symbol is treated as follows: If a function's symbol with the same symbol-name is externalised from the clip package, the clip function is used. If not, the function named by the symbol in the symbol's package is used. This is done so that, no matter your package, you will always have access to functions like clip and clipboard. As an unfortunate side-effect of a symbol not knowing whether it was fully qualified or not, this means that even if you use the full symbol name with package in your template, as long as the name is external in clip, the clip function is used instead. You will have to use a combination of funcall and #' to circumvent this limitation..

Further Reading

Package Index