NAME
Tiny::YAML - YAML::Tiny Done Right
PREAMBLE
Don't even look at this yet. It's a super early release and will be
bootstrapping for a while.
This module uses a real grammar to parse/load YAML.
Stay tuned...
TODO - Funny rant about the shortcomings of YAML::Tiny
SYNOPSIS
Assuming "file.yaml" like this:
---
rootproperty: blah
section:
one: two
three: four
Foo: Bar
empty: ~
Read and write "file.yaml" like this:
use Tiny::YAML;
# Open the config
my $data = Tiny::YAML::LoadFile( 'file.yaml' );
# Get a reference to the first document
my $config = $data->[0];
# Or read properties directly
my $root = $data->[0]->{rootproperty};
my $one = $data->[0]->{section}->{one};
my $Foo = $data->[0]->{section}->{Foo};
# Change data directly
$data->[0]->{newsection} = { this => 'that' }; # Add a section
$data->[0]->{section}->{Foo} = 'Not Bar!'; # Change a value
delete $data->[0]->{section}; # Delete a value
# Save the document back to the file
Tiny::YAML::DumpFile( 'file.yaml' );
To create a new YAML file from scratch:
# Create a new object with a single hashref document
my $data = Dump( { wibble => "wobble" } );
# Add an arrayref document
push @$data, [ 'foo', 'bar', 'baz' ];
# Save both documents to a file
$data->( 'data.yaml' );
Then "data.yaml" will contain:
---
wibble: wobble
---
- foo
- bar
- baz
DESCRIPTION
"Tiny::YAML" is a perl class for reading and writing YAML-style files,
written with as little code as possible, reducing load time and memory
overhead.
Most of the time it is accepted that Perl applications use a lot of
memory and modules. The "Tiny::" family of modules is specifically
intended to provide an ultralight and zero-dependency alternative to
many more-thorough standard modules.
This module is primarily for reading human-written files (like simple
config files) and generating very simple human-readable files. Note that
I said *human- readable* and not *geek-readable*. The sort of files that
your average manager or secretary should be able to look at and make
sense of.
Tiny::YAML does not generate comments, it won't necessarily preserve the
order of your hashes, and it will normalise if reading in and writing
out again.
It only supports a very basic subset of the full YAML specification.
Usage is targeted at files like Perl's META.yaml, for which a small and
easily- embeddable module is extremely attractive.
Features will only be added if they are human readable, and can be
written in a few lines of code. Please don't be offended if your request
is refused. Someone has to draw the line, and for Tiny::YAML that
someone is me.
If you need something with more power move up to YAML (7 megabytes of
memory overhead) or YAML::XS (6 megabytes memory overhead and requires a
C compiler).
To restate, Tiny::YAML does *not* preserve your comments, whitespace, or
the order of your YAML data. But it should round-trip from Perl
structure to file and back again just fine.
FUNCTIONS
Tiny::YAML implements a number of functions to add compatibility with
the YAML API. These should be a drop-in replacement.
"Dump"
my $string = Dump(list-of-Perl-data-structures);
Turn Perl data into YAML. This function works very much like
Data::Dumper::Dumper().
It takes a list of Perl data structures and dumps them into a
serialized form.
It returns a character string containing the YAML stream. Be sure to
encode it as UTF-8 before serializing to a file or socket.
The structures can be references or plain scalars.
Dies on any error.
"Load"
my @data_structures = Load(string-containing-a-YAML-stream);
Turn YAML into Perl data. This is the opposite of Dump.
Just like Storable's thaw() function or the eval() function in
relation to Data::Dumper.
It parses a character string containing a valid YAML stream into a
list of Perl data structures representing the individual YAML
documents. Be sure to decode the character string correctly if the
string came from a file or socket.
my $last_data_structure = Load(string-containing-a-YAML-stream);
For consistency with YAML.pm, when Load is called in scalar context,
it returns the data structure corresponding to the last of the YAML
documents found in the input stream.
Dies on any error.
"DumpFile(filepath, list)"
Writes the YAML stream to a file with UTF-8 encoding instead of just
returning a string.
Dies on any error.
"LoadFile(filepath)"
Reads the YAML stream from a UTF-8 encoded file instead of a string.
Dies on any error.
TINY YAML SPECIFICATION
This section of the documentation provides a specification for "Tiny
YAML", a subset of the YAML specification.
It is based on and described comparatively to the YAML 1.1 Working Draft
2004-12- 28 specification, located at
<
http://yaml.org/spec/current.html>.
Terminology and chapter numbers are based on that specification.
1. Introduction and Goals
The purpose of the Tiny YAML specification is to describe a useful
subset of the YAML specification that can be used for typical
document-oriented use cases such as configuration files and simple data
structure dumps.
Many specification elements that add flexibility or extensibility are
intentionally removed, as is support for complex data structures, class
and object-orientation.
In general, the Tiny YAML language targets only those data structures
available in JSON, with the additional limitation that only simple keys
are supported.
As a result, all possible Tiny YAML documents should be able to be
transformed into an equivalent JSON document, although the reverse is
not necessarily true (but will be true in simple cases).
As a result of these simplifications the Tiny YAML specification should
be implementable in a (relatively) small amount of code in any language
that supports Perl Compatible Regular Expressions (PCRE).
2. Introduction
Tiny YAML supports three data structures. These are scalars (in a
variety of forms), block-form sequences and block-form mappings.
Flow-style sequences and mappings are not supported, with some minor
exceptions detailed later.
The use of three dashes "---" to indicate the start of a new document is
supported, and multiple documents per file/stream is allowed.
Both line and inline comments are supported.
Scalars are supported via the plain style, single quote and double
quote, as well as literal-style and folded-style multi-line scalars.
The use of explicit tags is not supported.
The use of "null" type scalars is supported via the ~ character.
The use of *bool* type scalars is not supported.
However, serializer implementations should take care to explicitly
escape strings that match a *bool* keyword in the following set to
prevent other implementations that do support *bool* accidentally
reading a string as a boolean
true|false|null
The use of anchors and aliases is not supported.
The use of directives is supported only for the %YAML directive.
3. Processing Tiny YAML Information
Processes
The YAML specification dictates three-phase serialization and
three-phase deserialization.
The Tiny YAML specification does not mandate any particular
methodology or mechanism for parsing.
Any compliant parser is only required to parse a single document at
a time. The ability to support streaming documents is optional and
most likely non-typical.
Because anchors and aliases are not supported, the resulting
representation graph is thus directed but (unlike the main YAML
specification) *acyclic*.
Circular references/pointers are not possible, and any Tiny YAML
serializer detecting a circular reference should error with an
appropriate message.
Presentation Stream
Tiny YAML reads and write UTF-8 encoded files. Operations on strings
expect or produce Unicode characters not UTF-8 encoded bytes.
Loading Failure Points
Tiny YAML parsers and emitters are not expected to recover from, or
adapt to, errors. The specific error modality of any implementation
is not dictated (return codes, exceptions, etc.) but is expected to
be consistent.
4. Syntax
Character Set
Tiny YAML streams are processed in memory as Unicode characters and
read/written with UTF-8 encoding.
The escaping and unescaping of the 8-bit YAML escapes is required.
The escaping and unescaping of 16-bit and 32-bit YAML escapes is not
required.
Indicator Characters
Support for the "~" null/undefined indicator is required.
Implementations may represent this as appropriate for the underlying
language.
Support for the "-" block sequence indicator is required.
Support for the "?" mapping key indicator is *not* required.
Support for the ":" mapping value indicator is required.
Support for the "," flow collection indicator is *not* required.
Support for the "[" flow sequence indicator is *not* required, with
one exception (detailed below).
Support for the "]" flow sequence indicator is *not* required, with
one exception (detailed below).
Support for the "{" flow mapping indicator is *not* required, with
one exception (detailed below).
Support for the "}" flow mapping indicator is *not* required, with
one exception (detailed below).
Support for the "#" comment indicator is required.
Support for the "&" anchor indicator is *not* required.
Support for the "*" alias indicator is *not* required.
Support for the "!" tag indicator is *not* required.
Support for the "|" literal block indicator is required.
Support for the ">" folded block indicator is required.
Support for the "'" single quote indicator is required.
Support for the """ double quote indicator is required.
Support for the "%" directive indicator is required, but only for
the special case of a %YAML version directive before the "---"
document header, or on the same line as the document header.
For example:
%YAML 1.1
---
- A sequence with a single element
Special Exception:
To provide the ability to support empty sequences and mappings, support
for the constructs [] (empty sequence) and {} (empty mapping) are
required.
For example,
%YAML 1.1
# A document consisting of only an empty mapping
--- {}
# A document consisting of only an empty sequence
--- []
# A document consisting of an empty mapping within a sequence
- foo
- {}
- bar
Syntax Primitives
Other than the empty sequence and mapping cases described above, Tiny
YAML supports only the indentation-based block-style group of contexts.
All five scalar contexts are supported.
Indentation spaces work as per the YAML specification in all cases.
Comments work as per the YAML specification in all simple cases. Support
for indented multi-line comments is *not* required.
Separation spaces work as per the YAML specification in all cases.
Tiny YAML Character Stream
The only directive supported by the Tiny YAML specification is the %YAML
language/version identifier. Although detected, this directive will have
no control over the parsing itself.
The parser must recognise both the YAML 1.0 and YAML 1.1+ formatting of
this directive (as well as the commented form, although no explicit code
should be needed to deal with this case, being a comment anyway)
That is, all of the following should be supported.
--- #YAML:1.0
- foo
%YAML:1.0
---
- foo
% YAML 1.1
---
- foo
Support for the %TAG directive is *not* required.
Support for additional directives is *not* required.
Support for the document boundary marker "---" is required.
Support for the document boundary market "..." is *not* required.
If necessary, a document boundary should simply by indicated with a
"---" marker, with not preceding "..." marker.
Support for empty streams (containing no documents) is required.
Support for implicit document starts is required.
That is, the following must be equivalent.
# Full form
%YAML 1.1
---
foo: bar
# Implicit form
foo: bar
Nodes
Support for nodes optional anchor and tag properties is *not* required.
Support for node anchors is *not* required.
Support for node tags is *not* required.
Support for alias nodes is *not* required.
Support for flow nodes is *not* required.
Support for block nodes is required.
Scalar Styles
Support for all five scalar styles is required as per the YAML
specification, although support for quoted scalars spanning more than
one line is *not* required.
Support for multi-line scalar documents starting on the header is not
required.
Support for the chomping indicators on multi-line scalar styles is
required.
Collection Styles
Support for block-style sequences is required.
Support for flow-style sequences is *not* required.
Support for block-style mappings is required.
Support for flow-style mappings is *not* required.
Both sequences and mappings should be able to be arbitrarily nested.
Support for plain-style mapping keys is required.
Support for quoted keys in mappings is *not* required.
Support for "?"-indicated explicit keys is *not* required.
Here endeth the specification.
Additional Perl-Specific Notes
For some Perl applications, it's important to know if you really have a
number and not a string.
That is, in some contexts is important that 3 the number is distinctive
from 3 the string.
Because even Perl itself is not trivially able to understand the
difference (certainly without XS-based modules) Perl implementations of
the Tiny YAML specification are not required to retain the
distinctiveness of 3 vs 3.
SUPPORT
Bugs should be reported via the CPAN bug tracker at
"/github.com/ingydotnet/tiny-yaml- pm/issues" in http:
AUTHOR
Ingy döt Net <
[email protected]>
SEE ALSO
YAML::Tiny
YAML
YAML::Syck
Config::Tiny
CSS::Tiny
COPYRIGHT
Copyright 2014 Ingy döt Net
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
