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== Outdated egg!

This is an egg for CHICKEN 3, the unsupported old release.  You're almost certainly looking for [[/eggref/4/hart|the CHICKEN 4 version of this egg]], if it exists.

If it does not exist, there may be equivalent functionality provided by another egg; have a look at the [[https://wiki.call-cc.org/chicken-projects/egg-index-4.html|egg index]]. Otherwise, please consider porting this egg to the current version of CHICKEN.

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== hart

The {{hart}} egg provides an SXML-inspired syntax for HTML generation.

== Authors

[[Graham Fawcett]]

== Requirements

* [[http://code.call-cc.org/legacy-eggs/3/vector-lib.html|vector-lib]]

== Examples

<enscript highlight=scheme>
(use hart)
(define people '((Fred fred@example.net 25) (Mary mary@example.net 33)))
(hart (html (head (title "People"))
            (body (h1 (fmt: "A list of ~a people" (length people)))
                  (if: (null? people)
                       (h2 "No people!")
                       (ol (for: ((name email age) people)
                             (li (a (@ (href (conc "mailto:" email)))
                                    (text: name))
                                 (fmt: ", who is ~a years old." age))))))))
</enscript>

which produces

<enscript highlight=html>
<html><head><title>People</title></head><body>
<h1>A list of 2 people</h1>
<ol><li><a href="mailto:fred@example.net">Fred</a>, who is 25 years old.</li>
<li><a href="mailto:mary@example.net">Mary</a>, who is 33 years old.</li>
</ol></body></html>
</enscript>

== Syntax

[syntax] (hart hart-expr ...)
 [syntax] (hart->string hart-expr ...)

Compiles hart-expr, an expression in the Hart syntax. In short, Hart is SXML syntax plus a set of "keyword expressions" which handle flow-control, iteration, escaping, etc.

(hart) outputs to (current-output-port) and returns an undefined value. (hart->string) returns a string value.

Multiple expressions can be passed to (hart) and (hart->string): there is an implicit (let: () ...) enclosing the expressions (see let: below).

=== Keyword expressions

[syntax] (if: expr hart-true hart-false)
 [syntax] (when: expr hart-true*)
 [syntax] (unless: expr hart-false*)

These are like their Scheme counterparts, except hart-true and hart-false are expressions in Hart syntax.

[syntax] (for: (iter-expr list-or-vec) . hart-body)

A looping construct. The iter-expr is a match-expression which is matched to each successive value in list-or-vec. Hart-body is a list of Hart expressions, evaluated for each value of iter-expr.

[syntax] (let: let-forms . hart-body)
 [syntax] (let*: let-forms . hart-body)
 [syntax] (letrec: let-forms . hart-body)

Like a (let ...) expression, but hart-body is a list of Hart expressions.

=== Formatting keywords

[syntax] (raw: . expr)

The Scheme expressions (not Hart!) are evaluated to strings and outputted, without HTML/XML escaping.

[syntax] (text: . exprs) or (t: . exprs)

The Scheme expressions are evaluated to strings, HTML-escaped, and outputted.

[syntax] (fmt: format-string . args)

The result of (apply format format-string args) is HTML-escaped and outputted.

[syntax] (scheme: . exprs)

The Scheme expressions are evaluated. If they produce output, that output will be inserted into the HTML.

== Attributes

Note that attributes (such as the "href" in an A tag) are of the form (name value), where "name" is a string or symbol, and "value" is a Scheme expression (literal or otherwise). No escaping is done on these expressions at the current time. 
=== Optional Attributes

An attribute whose value evaluates to #f will be omitted from the HTML output. This provides a mechanism for specifying optional attributes.

== Utility functions

[procedure] (hart-html-escape string)

A fast, basic HTML-escaping routine.

== History

* Version 1.3.0 (2008-03-15): 'syntax-case' support [Kon Lovett]
* Version 1.2.1 (2008-02-22): bugfix release (removed bad build dependency)
* Version 1.2 (2008-02-20): bugfix in hart.setup; added -O1 optimization
* Version 1.1.2 (February 2008): bugfix releae

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