YML – Why a Markup Language?!
Well, it's the idea not to need to define a grammar first when you want to use a Domain Specific Language. For that purpose, YML is being translated into XML. Let's make an example.
Everything which comes close to a C like language, parses without a grammar definition:
This:
template< class T > T max(T a, T b);
Parses to:
<?xml version='1.0' encoding='UTF-8'?>
<template>
<generic>
<class/>
<T/>
</generic>
<T>
<max>
<parm>
<T/>
<a/>
</parm>
<parm>
<T/>
<b/>
</parm>
</max>
</T>
</template>
Instead of defining grammars, you test out and play around until the results are matching your needs. If the resulting tree does not fit what you're expecting, change it by patching the grammar with decl
:
This:
module A {
interface B {
attribute long n;
};
};
Parses to:
<?xml version='1.0' encoding='UTF-8'?>
<module>
<A>
<interface>
<B>
<attribute>
<long>
<n/>
</long>
</attribute>
</B>
</interface>
</A>
</module>
This does not look like what we want. So we tell YML that we have a module name after the module, an interface name after the interface and type and name after the attribute:
This:
decl module @name;
decl interface @name;
decl attribute @type @name;
module A {
interface B {
attribute long n;
};
};
Parses to:
<?xml version='1.0' encoding='UTF-8'?>
<module name="A">
<interface name="B">
<attribute type="long" name="n"/>
</interface>
</module>
With YML you can:
use a C-like DSL without writing a grammar first
generate code out of any XML based language like SVG using YSLT
define a wiki like language in just a few lines like YHTML does
replace bad designed and complicated XML languages with simpler C-like ones
... and much more.
Just writing down what I wanted to have instead of XML for a sample:
<list name="List of goods">
<head>
<columTitle>
Goods
</columnTitle>
<columnTitle>
Price
</columnTitle>
</head>
<row>
<value>
Beer
</value>
<value>
20
</value>
</row>
<row>
<value>
Wine
</value>
<value>
30
</value>
</row>
</list>
Something like that should be more easy, say, like this:
list "List of goods" {
head title "Goods", title "Price";
row value "Beer", value 20;
row value "Wine", value 30;
}
The latter is what I call an Y language – a language specified in YML. How could this be achieved? Well, what's to do? To have the required information, how to build XML from the script above, we need:
name
, while Goods
is the text value of a tagtitle
shout be written out as columnTitle
How to do that? Let's invent a simple definition language for that information:
decl list(name);
decl title alias columnTitle;
Here you can download the complete list sample.