Re: sfx: baby steps of an html templating engine based on skribillo's skribe reader and sxml

[Amirouche Boubekki]

Le 2015-07-30 13:55, Amirouche Boubekki a écrit :
> Héllo,
>
>
> I've been lurking around skribillo and artanis. I don't really like
> the rails-like syntax
> of artanis, even if it has its use-cases and I wanted to hack on
> something "small", so
> I've put together sfx.
>
> The code of skribe reader is included in sfx.scm. So the only
> dependency is guile (2.0.11) and
> guile-reader that you can install using `guix package -i guile-reader`.
>
> This bare template language has the following features:
>
> - wanna be simpler sxml syntax
> - templates with custom environment
> - external libraries loading inside the template
>
>
> # Wanna be simpler sxml syntax
>
> Skribe reader (implemented with guile-reader) provide a handy syntax to
> both define keywords and quasiquote. In an sxml context those features
> are used to implemented attributes and text nodes.
>
> ## attributes
>
> Attributes in sxml are defined as follow:
>
>   (div (@ (id "shell")) "This the main area")
>
> Instead of requiring the nesting of `(attribute-name attribute-value)` 
> sfx use
> the simpler keyword syntax `:keyword`. The above snippet becomes:
>
>   (div (@ :id "shell") "This the main area")
>
> I'm not sure it's worth the trouble of diverting from sxml standard.
> That said, it looks
> more like plain xml.
>
> ## text nodes
>
> Text nodes can be defined as
>
>   (p [héllo hacker])
>
> This is looks the same as the default reader. It becomes handy when
> you include an
> inline element inside the text node:
>
>   (p [héllo ,(b [hacker])
>
> `,()` is a special syntax of skribe reader which provides `(unquote)`
> inside [bracket] `quasiquote`.
>
> With the default guile reader, this must be written as:
>
>   (p "héllo " (b "hacker"))
>
> This is looks verbose and prone to error. One must not forget the space 
> in the
> string before the `(b)` element.
>
>
> # templates with custom environment
>
> Right now this part of the template language is not really
> userfriendly. But you can pass custom
> variables to the template but those must be parameters. In the example
> sfx.scm (which includes
> example use of the procedures) the environment in which the template
> is evaled is defined as follow:
>
>   (define value (make-parameter 42))
>   (define amirouche (make-person "amirouche" 30))
>   (define env (let ((value value)
>                     (amirouche amirouche))
>                 (the-environment)))
>
>
> Then `value` can be echo'ed inside the template using the unquote
> syntax `,()`, e.g.
>
>    (p [Here is a lucky number for you «,(value)»])
>
> As you can see the previous snippet, there is also a `<record>` record
> inside the environment.
> One can (maybe) provide in the environment the required procedures to
> echo the correct
> fields but this is verbose. Instead sfx use `(use-modules)` inside the
> template definition
> file. This is presented in the following and last part.
>
> # external libraries loading inside the template
>
> Currently it's (only) possible to do `(use-modules)` inside the
> template file. The template
> file looks like the following:
>
> ```
> (use-modules (person))
>
> `(html
>   (body
>     (p [My name is ,(person-name amirouche)])))
> ```
>
> I could not make procedure definition work inside the template, this
> my be linked to the way
> I eval the template. It's shame because for quick and dirty hacks it
> can be handy like defining
> mini-templates inside the big template.
>
>
>
>
>
> This is my second try at this and having a look at the code of haunt
> [1] was helpful.
>
> Hope this helps!
>
>
> [1] https://git.dthompson.us/haunt.git

Sorry for the double posting. This mail is not a duplicate.

I though that the implementation `extend` would be more involving.

`extend` is the dual of `include`. Given a base template `base.sfx` you 
define placeholders
say `,(main)` and `,(sidebar)` and the rest is the "shell" of the 
application ie. the part of
GUI that is always the same over the application.

If `index.sfx` inherit `base.sfx` the context in which `base.sfx` is 
rendered is the same as the context
used to render `ìndex.sfx` plus the variables defined/passed in 
`ìndex.sfx` to `base.sfx`.

In the following example, `title` and `intro` are evaled and then added 
to `(current-module)` environment
with which `base.sfx` is rendered.

   (extend "base.sfx"
           (current-module)
           `((title `(h1 [Héllo again hacker!!]))
             (intro "This is a little presentation of sfx template 
language")))

I don't how to make `(current-module)` disappear but it's also more 
explicit. I'm not sure.

`extend` implement a pattern similar to inheritance in OOP.

I attach complete code with an example. There is small doc in the header 
of the file.

sfx.scm
Description: Text document

base.sfx
Description: Text document

index.sfx
Description: Text document