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List:       puppet-dev
Subject:    [Puppet-dev] Booleans, 'if', and similar pursuits.
From:       luke () madstop ! com (Luke Kanies)
Date:       2006-07-21 22:35:40
Message-ID: 44C156BC.9090604 () madstop ! com
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So, I've got a feature request in to myself to add an 'if' keyword, 
because I keep doing statements like this:

define mything(useit = false) {
   case $useit {  false: {}
     default: { ... }
   }
}

It would be tons cleaner like this:

define mything(useit = false) {
   if $useit { ... }
}

If I add this, though, I almost have to add, at the same time, at least 
the ability to negate the test with '!', and probably an '||' operator 
and a '&&' operator.  This is enough complexity (since almost no 
statements in Puppet currently have values) that I'm considering this a 
relatively large stand-alone project in the parser, not just a quick 
additional statement type.

This gets me thinking about booleans, though, and about -- other 
problems aside -- how nice cfengine's class booleans are.  Puppet has 
just started to be able to manipulate a global boolean dictionary called 
'tags', which are basically equivalent to cfengine's classes, but they 
require separate functions to manipulate:

   tag(mytag)
   tagged(mytag)

I'm thinking about creating a top-level boolean type that maps to these 
tags, and then just using a different sigil, like '@' or '~'.  As I 
create more complex configurations in Puppet, and I start to think about 
how to really use these tags, I realize that it's pretty verbose to try 
to use them right now, what with needing the case statement and the 
function.  Compare this cfengine code:

files:
   hostname:: /my/file ...

To this Puppet code:

case tagged($hostname) {
   true: {
     file { "/my/file": ... }
   }
}

Admittedly, a large part of the verbosity there is gratuitous curly 
braces, and I should be fixing that anyway, but I don't like the 
explicit mention of "true" here.

I'm thinking maybe something like this:

if @hostname {
   file { "/my/file": ... }
}

And when curlies become largely optional (i.e., when I become a better 
grammar writer), that would be even cleaner.  I used to think curlies 
looked so clean...

-- 
Sapolsky's First Law:
     Think logically, but orthogonally.
---------------------------------------------------------------------
Luke Kanies | http://reductivelabs.com | http://madstop.com


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