DSL Quest: A WAT Safari - PuppetConf 2013

Nick’s DSL Quest:
WAT Safari
Nick Fagerlund
Technical Writer | Puppet Labs
@nfagerlund
Friday, August 23, 13

puppetconf.com #puppetconf
So okay,there I was.

When I first got here,we
had this “language
tutorial.”

It was a bit of
a mess.
(“Additional language
features…?”)

The Puppet language
accreted over time.

(And so did the docs.)

So I had a good/bad idea.

Here’s what I found.

$subj
=
{t
=>
'r',
u
=>
'e'}
notice(str2bool("$subj"))
T to the R

$subj
=
{t
=>
'r',
u
=>
'e'}
notice(str2bool("$subj"))
true
T to the R

@notify
{'one
tag':

tag
=>
'one',
}
@notify
{'two
tags':

tag
=>
['one',
'two'],

#before
=>
Notify['three
tags']
}

@notify
{'three
tags':

tag
=>
['one',
'two',
'three'],

noop
=>
undef,
}

Let’s talk about collectors

Notify
<|
tag
==
'one'
|>
Notice:
Compiled
catalog
for
magpie.lan
in
environment

production
in
0.11
seconds
Notice:
one
tag
Notice:
/Stage[main]//Notify[one
tag]/message:
defined

'message'
as
'one
tag'
Notice:
three
tags
Notice:
/Stage[main]//Notify[three
tags]/message:
defined

'message'
as
'three
tags'
Notice:
two
tags
Notice:
/Stage[main]//Notify[two
tags]/message:
defined

'message'
as
'two
tags'

Notify
<|
'one'
==
tag
|>
Error:
Could
not
parse
for
environment
production:
Syntax

error
at
'one';
expected
'|>'
at
/Users/nick/Documents/
manifests/collector-‐search.pp:29
on
node
magpie.lan

Notify
<|
tag
==
['one',
'two']
|>
Notice:
Compiled
catalog
for
magpie.lan
in
environment

production
in
0.09
seconds
Notice:
one
tag
Notice:
/Stage[main]//Notify[one
tag]/message:
defined

'message'
as
'one
tag'
Notice:
three
tags
Notice:
tags]/message:
defined

'message'
as
'three
tags'
Notice:
two
tags
Notice:
tags]/message:
defined

'message'
as
'two
tags'
Notice:
Finished
catalog
run
in
0.17
seconds

Notify
<|
tag
!=
['one',
'two']
|>
Notice:
Compiled
catalog
for
magpie.lan
in
environment

production
in
0.09
seconds
Notice:
three
tags
Notice:
tags]/message:
defined

'message'
as
'three
tags'
Notice:
two
tags
Notice:
tags]/message:
defined

'message'
as
'two
tags'
Notice:
Finished
catalog
run
in
0.18
seconds

CONCLUSION:
“==” != “==”

class
class
{

notify
{'hey
it
worked':}
}
include
class
Results
Classy

class
class
{

notify
{'hey
it
worked':}
}
include
class
Error:
Could
not
parse
for
environment

production:
Syntax
error
at
'class'
at
/
Users/nick/Documents/manifests/
class_class.pp:6
on
node
magpie.lan
Classy

class
class
{

notify
{'hey
it
worked':}
}
include
"class"
Classy

class
class
{

notify
{'hey
it
worked':}
}
include
"class"
Notice:
Compiled
catalog
for
magpie.lan
in
environment

production
in
0.09
seconds
Notice:
hey
it
worked
Notice:
/Stage[main]/Class/Notify[hey
it
worked]/message:

defined
'message'
as
'hey
it
worked'
Notice:
Finished
catalog
run
in
0.19
seconds
Classy

class
parent
{

define
doessomething
{
notice("parentvar
is
set,
in
the

parent::doessomething
define")
}

class
whoa
{
notice("Okay
that
works
w/
classes
too")
}

$otherparentvar
=
"haha
whoa"
}
search('parent')
doessomething{'something':}
include
whoa
notice($otherparentvar)
#
This
one
doesn't
work
though,
because

it
attaches
the
NAMESPACE,
not
the
scope.
Search???

class
parent
{

define
doessomething
{
notice("parentvar
is
set,
in
the

parent::doessomething
define")
}

class
whoa
{
notice("Okay
that
works
w/
classes
too")
}

$otherparentvar
=
"haha
whoa"
}
search('parent')
doessomething{'something':}
include
whoa
notice($otherparentvar)
#
This
one
doesn't
work
though,
because

it
attaches
the
NAMESPACE,
not
the
scope.
It
dumps
a
random
namespace
into
the
local

namespace???
Search???

(This is still in Puppet 3.2.)
(photo via http://
weheartit.com/entry/
68358166)

[
Notify['first'],
Notify['second']
]
It’s
an
array
of
resource
references,
right?
Have you seen this syntax?

Notify[
'first',
'second'
]
???
How about this one?

Notify[
['first',
'second']
]
(Okay,
it
ends
up
being
the
same
as
the
last
one
for
some

reason.)
How about this one?

#
OK
require
=>
Notify['first',
'second']
require
=>
[
Notify['first'],
Notify['second']
]
Notify['first',
'second']
-‐>
Notify['third']
#
BAD
[
Notify['first'],
Notify['second']
]
-‐>

Notify['third']
?????!!
They all look kind of similar?

#
OK
Notify['first',
'second']
{

message
=>
'Adding
a
message
to
these.'
}
#
BAD
[
Notify['first'],
Notify['second']
]
{

message
=>
'Adding
a
message
to
these.'
}
?????!!
They all look kind of similar?

So,these are two
completely different
syntaxes. (I named the
non-array one “multi-
references.)

class
bar
{

notice("From
class
bar")
}
class
foo::bar
{

notice("From
class
foo::bar")
}
class
foo
{

include
bar
}
include
foo
Include bar... but only as a last
resort

class
bar
{

notice("From
class
bar")
}
class
foo::bar
{

notice("From
class
foo::bar")
}
class
foo
{

include
bar
}
include
foo
Notice:
Scope(Class[Foo::Bar]):
From
class
foo::bar
(this
is
bug
#2053.)
Include bar... but only as a last
resort

#
Is
the
==
operator
case-‐sensitive?
NO
notice(
'eat'
==
'EAt'
)
#
Is
the
'in'
operator
case-‐sensitive?
YES
notice(
'eat'
in
'EAten'
)
Notice:
Scope(Class[main]):
true
Notice:
Scope(Class[main]):
false
Case sensitivity training

ANYWAY

#
The
$is_virtual
fact
is
false
on
this
machine
if
$is_virtual
{

notice("Guess
this
is
a
virtual
machine!")
}
Falseness is truth

#
The
$is_virtual
fact
is
false
on
this
machine
if
$is_virtual
{

notice("Guess
this
is
a
virtual
machine!")
}
Notice:
Scope(Class[main]):
Guess
this
is
a
virtual

machine!
Falseness is truth

(Use the str2bool()
function from
puppetlabs/stdlib)

This,of course,escalated
quickly.

Code
Results
What IS truth,anyway?

$x
=
5
$y
=
3
notice("Value
of
x
is
${x}")
You’ve
seen
this
before.
Express yourself

$x
=
5
$y
=
3
notice("Five
by
three
is
${$x
*
$y}")
Express yourself

$x
=
5
$y
=
3
notice("Five
by
three
is
${$x
*
$y}")
Notice:
Scope(Class[main]):
Five
by
three
is
15
Express yourself

$mystring
=
"Nothing
in
particular"
notice("But
it
was
${$mystring
=~
/thing/}")
Notice:
Scope(Class[main]):
But
it
was
true
Express yourself
Whoa

notice("This
time
with
an
in
statement:
Is
there

a
thing
in
nothing?
${"thing"
in
$mystring}
so

yeah")
Notice:
Scope(Class[main]):
This
time
with
an
in

statement:
Is
there
a
thing
in
nothing?
true
so
yeah
Express yourself

notice("There's
a
function
operand
in
here:

${
fqdn_rand(30)
+
'90'
}
so
yeah")
WELL,
at
least
THAT
one
doesn’t
work.
Express yourself

notice("Variable
with
doubled
sigil:
${
$x}
so

yeah")
notice("Singular
sigil,
but
with
wacky
spacing:

${

x}
so
yeah")
Notice:
Scope(Class[main]):
Variable
with
doubled
sigil:

5
so
yeah
Notice:
Scope(Class[main]):
Singular
sigil,
but
with

wacky
spacing:
5
so
yeah
Express yourself

notice("Yo
dawg,
I
heard
you
like
${"strings,
so

I
put
a
string
in
your"}
string")
Sorry
for
partying
like
it’s
200X,
but
anyway
yeah,
that

totally
works.
Express yourself

#
What
about
this?

notice("Twenty
by
eighty
is
${
20
*
80
}
so

yeah")
Error:
left
operand
of
*
is
not
a
number
Express yourself

notice("Twenty
by
eighty
is
${
'20'
*
'80'
}
so

yeah")
Notice:
Scope(Class[main]):
Twenty
by
eighty
is
1600
so

yeah
Express yourself

And at this point I was like

(It turns out the first bareword in an
interpolation block gets silently
turned into a variable,so 20 became
$20,which would be a regex capture
variable except we weren’t inside a
conditional so it was undef???)

So then I was like

yeah

file
{'file1':

path
=>
'/tmp/file1',

ensure
=>
file,

alias
=>
['othername',
'fourthname'],
}
file
{'file2':

path
=>
'/tmp/file2',

ensure
=>
file,

before
=>
File['othername'],
}
Let’s talk about aliases

file
{'file1':

path
=>
'/tmp/file1',

ensure
=>
file,

alias
=>
['othername',
'fourthname'],
}
file
{'file2':

path
=>
'/tmp/file2',

ensure
=>
file,

before
=>
File['othername'],
}
This
works
fine.

file
{'file1':

alias
=>
['othername',
'fourthname'],
}
file
{'file2':}
File['file2']
-‐>
File['othername']
Error:
Could
not
find
resource
'File[othername]'
for

relationship
from
'File[file2]'
on
node
magpie.lan
So
it
works
in
metaparameters,
but
not
in
chaining

statements.

Okay!

@file
{'file1':

path
=>
'/tmp/file1',

ensure
=>
file,

alias
=>
['othername',
'fourthname'],
}
realize
File['othername']
Nope!

@file
{'file1':

path
=>
'/tmp/file1',

ensure
=>
file,

alias
=>
['othername',
'fourthname'],
}
realize
File['/tmp/file1']
Nope!

@file
{'file1':

path
=>
'/tmp/file1',

ensure
=>
file,

alias
=>
['othername',
'fourthname'],
}
File
<|
alias
==
'fourthname'
|>
PURRS
LIKE
A
KITTEN!

Anyway,what did I learn?
(In the larger sense,not in
the str2bool({t => ‘r’,u =>
‘e’}) sense.)

Do science to it.

Long-lived systems get
weird.

Talk to the old-timers.

WAT brings us together!

(Pause here for general
theory of the social capital
of WAT in engineering
cultures.)

And venting about WAT
can keep your morale up.
Because c’mon.
That’s pretty funny.

https://
github.com/
nfagerlund/
evil-made-
manifest
(photo via http://
taterpie.tumblr.com/
post/56826040138/
thats-an-awesome-
shot)

Thank You
Nick Fagerlund
Technical Writer | Puppet Labs
@nfagerlund
Collaborate. Automate. Ship.

Follow us on Twitter @puppetlabs
youtube.com/puppetlabsinc
slideshare.net/puppetlabs
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DSL Quest: A WAT Safari - PuppetConf 2013

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