Thread: Re: [Webmacro-devel] #templet directive (Page 2)

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I don't think the "to" option is worthwhile.  You can accomplish the same
thing with a simple #setblock:

#setblock $var { #eval $templet using $map }

So that leaves just:

#eval $templet

and

#eval $templet using $map

the first syntax is actually the same as just

$templet

so we might leave that out as well.  Simple is good.

Keats

----- Original Message -----
From: Lane Sharman
To: Keats
Cc: Sebastian Kanthak ; web...@li...
Sent: Thursday, June 26, 2003 12:34 AM
Subject: Re: [Webmacro-devel] #templet directive

Directives are just that. They provide direction and control over the flow.
A Directive is an intrinsic keyword for the WebMacro parser and evaluation
engine.

A property is an operator returning void, null, or an object. In the latter
case, the object's string representation is added to the stream unless we
are talking about assignment: #set $foo = $bar. A property is expanded. A
directive is interpreted.

As to the output directive, I agree that it complicates things. I think we
should stick with directives which enhance the language. Property tools are
the right place to do transformations and evaluations. I think we could use
some that are more utilitarian for those who are creating non-web text and
interacting with data flows as occurs in application integration.

Can we finalize #templet now?

#eval $template using { "foo":"a", "bar":"b" }
#eval $template to $variable using { "foo":"a", "bar":"b" }
#eval $template
#eval $template to $variable

Would be the #eval variations as I see them. The first two create an
explicit context and the last two use the current context. The using ...
option provides a nice way of creating a private context for the templet.
The using ... option implies that the templet cannot update the context of
the invoker.

-Lane

Keats wrote:

I think your inference is falacious.  Many directives write to the output
stream, some use block arguments and some don't.  The #include directive
writes to the stream without a block arg.  (And of course macros do this,
but that's another issue.)

I do think that a clear distinction between "expansion" -- putting something
into the output stream, and "evaluation" -- performing some computation,
would be helpful, but I can't think of a good way to do this without
radically changing the WM syntax.

It seems like the pattern that we've developed is that you use tools or
functions for basic value transformations -- HTMLEscape, URLEncode,
Math.mod, etc -- and directives for everything else.

Better documentation would probably help here.  Perhaps a taxonomy of
directives, like:

Control flow directives:

#if/#elseif/#else
#foreach
#count

Context altering directives (variable creation):

#set
#setblock
#const/#attribute/#param
#macro
#alternate
#bean
#templet

Text expansion directives:

#include
#eval
#text

Other:

#comment
#type
#profile

Keats

----- Original Message -----
From: "Sebastian Kanthak" <seb...@mu...>
To: "Keats" <ke...@ea...>
Cc: <web...@li...>
Sent: Wednesday, June 25, 2003 3:25 PM
Subject: Re: [Webmacro-devel] #templet directive

Hi,

On Monday 23 June 2003 16:37, Keats wrote:

You could still do this sort of thing with the $Template tool.  People
didn't seem to like the template tool syntax, so I came up with the
directive approach which seems a bit more user friendly.

My approach to the above would be to use a directive for the writer, say
#output

ok, let's forget about the output thing. I only used this as an example.

Like

Brian, I personally do not think think it is necessary, but if Lane has a
need for it, it's ok.

My problem with the #eval-directive is of a more general nature:

In WebMacro we basically have to possibilities to control the result of a
template evaluation:

1) We can insert something into the output stream. This is usually done by

a

property reference $foo.bar

2) We can interact with the template engine and tell it to iterate certain
blocks, chose one depending on a condition, set some properties and so on.

Intuitively I think, that writing something into the output-stream (point

1)

should be done via property references of the form $... and point 2 should

be

done via directives.

Or to put it the other way round: I believe, that directives should not

output

anything by themselves. Of course the "#foreach" directive outputs a lot,

but

that comes from the block inside the directive, not from the directive
itself. The same holds for "#if" and "#set" does not output anything at

all.

This is similar to the distinction between statements and expressions in

most

programming languages. I just realized, that this is how I thought about
directives and property-refernces until now.

In this picture a #templet directive would fit quite nice, because it just
declares a template. However, for evaluating, I would find a $... syntax
nicer.

However, I must admit, that there exists directives (like those declared

from

macros), that do not fit in my own schema, so it is probably broken.

But perhaps we can have some discussion about it: Do we have a consistent
guideline, when to use $... syntax (via tools or macros) and when to use
directives? I do not know of one and this is, where my confusion comes

from.

Sebastian

--
Sebastian Kanthak
PGP/GnuPG: http://www.muehlheim.de/~skanthak/pgp.html

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