YAML::PP - YAML 1.2 processor
WARNING: This is highly experimental.
Here are a few examples of what you can do right now:
use YAML::PP; my $ypp = YAML::PP->new; my @documents = $ypp->load_string($yaml); my @documents = $ypp->load_file($filename); my $yaml = $ypp->dump_string($data1, $data2); $ypp->dump_file($filename, $data1, $data2); # The loader offers JSON::PP::Boolean, boolean.pm or # perl 1/'' (currently default) for booleans my $ypp = YAML::PP->new(boolean => 'JSON::PP'); my $ypp = YAML::PP->new(boolean => 'boolean'); my $ypp = YAML::PP->new(boolean => 'perl'); # Legacy interface use YAML::PP qw/ Load Dump LoadFile DumpFile /; my @documents = Load($yaml); my @documents = LoadFile($filename); my $yaml = = Dump(@documents); DumpFile($filename, @documents);
Some utility scripts:
# Load YAML into a data structure and dump with Data::Dumper yamlpp5-load < file.yaml # Load and Dump yamlpp5-load-dump < file.yaml # Print the events from the parser in yaml-test-suite format yamlpp5-events < file.yaml # Create ANSI colored YAML yamlpp5-highlight < file.yaml # Parse and emit events directly without loading yamlpp5-parse-emit < file.yaml
This is Yet Another YAML Framework. For why this project was started, see "WHY".
The parser aims to parse YAML 1.2. See http://yaml.org/.
YAML 1.2
You can check out all current parse and load results from the yaml-test-suite here: https://perlpunk.github.io/YAML-PP-p5/test-suite.html
The Lexer is reading the YAML stream into tokens. This makes it possible to generate syntax highlighted YAML output.
Note that the API to retrieve the tokens will change.
The Parser retrieves the tokens from the Lexer. The main YAML content is then parsed with the Grammar.
The Constructor creates a data structure from the Parser events.
The Loader combines the constructor and parser.
The Dumper will delegate to the Representer
The Representer will create Emitter events from the given data structure.
The Emitter creates a YAML stream.
Still TODO:
Flow style is partially implemented.
Not yet working: Implicit flow collection keys, implicit keys in flow sequences, content directly after the colon, empty nodes, explicit keys
If you have valid YAML that's not parsed, or the other way round, please create an issue.
You will see line and column numbers in the error message. The column numbers might still be wrong in some cases.
The error messages need to be improved.
Currently loaded as single characters without validating
The Constructor now supports all three YAML 1.2 Schemas, Failsafe, JSON and Core.
You can choose the Schema, however, the API for that is not yet fixed. Currently it looks like this:
my $ypp = YAML::PP->new(schema => ['JSON']); # default is 'Core' for now
The Tags !!seq and !!map are still ignored for now.
!!seq
!!map
It supports:
Like in modules like YAML, the Constructor will use references for mappings and sequences, but obviously not for scalars.
You can choose between 'perl' (1/'', currently default), 'JSON::PP' and 'boolean'.pm for handling boolean types. That allows you to dump the data structure with one of the JSON modules without losing information about booleans.
'perl'
'JSON::PP'
'boolean'
Numbers are created as real numbers instead of strings, so that they are dumped correctly by modules like JSON::PP or JSON::XS, for example.
See "NUMBERS" for an example.
TODO:
Mapping Keys in YAML can be more than just scalars. Of course, you can't load that into a native perl structure. The Constructor will stringify those keys with Data::Dumper instead of just returning something like HASH(0x55dc1b5d0178).
HASH(0x55dc1b5d0178)
Example:
use YAML::PP; use JSON::PP; my $ypp = YAML::PP->new; my $coder = JSON::PP->new->ascii->pretty->allow_nonref->canonical; my $yaml = <<'EOM'; complex: ? ? a: 1 c: 2 : 23 : 42 EOM my $data = $yppl->load_string($yaml); say $coder->encode($data); __END__ { "complex" : { "{'{a => 1,c => 2}' => 23}" : 42 } }
Tags are completely ignored.
I would like to generate a complete parse tree, that allows you to manipulate the data structure and also dump it, including all whitespaces and comments. The spec says that this is throwaway content, but I read that many people wish to be able to keep the comments.
The Dumper should be able to dump strings correctly, adding quotes whenever a plain scalar would look like a special string, like true, or when it contains or starts with characters that are not allowed.
true
Most strings will be dumped as plain scalars without quotes. If they contain special characters or have a special meaning, they will be dumped with single quotes. If they contain control characters, including <"\n">, they will be dumped with double quotes.
It will recognize JSON::PP::Boolean and boolean.pm objects and dump them correctly.
TODO: Correctly recognize numbers which also have a string flag, like:
my $int = 23; say "int: $int"; # $int will now also have a PV flag
The layout is like libyaml output:
key: - a - b - c --- - key1: 1 key2: 2 key3: 3 --- - - a1 - a2 - - b1 - b2
my $ypp = YAML::PP->new; # load booleans via boolean.pm my $ypp = YAML::PP->new( boolean => 'boolean' ); # load booleans via JSON::PP::true/false my $ypp = YAML::PP->new( boolean => 'JSON::PP' ); # use YAML 1.2 Failsafe Schema my $ypp = YAML::PP->new( schema => ['Failsafe'] ); # use YAML 1.2 JSON Schema my $ypp = YAML::PP->new( schema => ['JSON'] ); # use YAML 1.2 Core Schema my $ypp = YAML::PP->new( schema => ['Core'] ); # Die when detecting cyclic references my $ypp = YAML::PP->new( cyclic_refs => 'fatal' ); # Other values: # warn - Just warn about them and replace with undef # ignore - replace with undef # allow - Default my $ypp = YAML::PP->new( boolean => 'JSON::PP', schema => ['JSON'], cyclic_refs => 'fatal', );
my $doc = $ypp->load_string("foo: bar"); my @docs = $ypp->load_string("foo: bar\n---\n- a");
Input should be utf-8 decoded.
my $doc = $ypp->load_file("file.yaml"); my @docs = $ypp->load_file("file.yaml");
UTF-8 decoding will be done automatically
my $yaml = $ypp->dump_string($doc); my $yaml = $ypp->dump_string($doc1, $doc2); my $yaml = $ypp->dump_string(@docs);
Output will be UTF-8 decoded
$ypp->dump_file("file.yaml", $doc); $ypp->dump_file("file.yaml", $doc1, $doc2); $ypp->dump_file("file.yaml", @docs);
File will be written UTF-8 encoded
Compare the output of the following YAML Loaders and JSON::PP dump:
use JSON::PP; use Devel::Peek; use YAML::XS (); use YAML (); $YAML::Numify = 1; # since version 1.23 use YAML::Syck (); $YAML::Syck::ImplicitTyping = 1; use YAML::Tiny (); use YAML::PP; my $yaml = "foo: 23"; my $d1 = YAML::XS::Load($yaml); my $d2 = YAML::Load($yaml); my $d3 = YAML::Syck::Load($yaml); my $d4 = YAML::Tiny->read_string($yaml)->[0]; my $d5 = YAML::PP->new->load_string($yaml); Dump $d1->{foo}; Dump $d2->{foo}; Dump $d3->{foo}; Dump $d4->{foo}; Dump $d5->{foo}; say encode_json($d1); say encode_json($d2); say encode_json($d3); say encode_json($d4); say encode_json($d5); SV = PVIV(0x55bbaff2bae0) at 0x55bbaff26518 REFCNT = 1 FLAGS = (IOK,POK,pIOK,pPOK) IV = 23 PV = 0x55bbb06e67a0 "23"\0 CUR = 2 LEN = 10 SV = PVMG(0x55bbb08959b0) at 0x55bbb08fc6e8 REFCNT = 1 FLAGS = (IOK,pIOK) IV = 23 NV = 0 PV = 0 SV = IV(0x55bbaffcb3b0) at 0x55bbaffcb3c0 REFCNT = 1 FLAGS = (IOK,pIOK) IV = 23 SV = PVMG(0x55bbaff2f1f0) at 0x55bbb08fc8c8 REFCNT = 1 FLAGS = (POK,pPOK,UTF8) IV = 0 NV = 0 PV = 0x55bbb0909d00 "23"\0 [UTF8 "23"] CUR = 2 LEN = 10 SV = PVMG(0x55bbaff2f6d0) at 0x55bbb08b2c10 REFCNT = 1 FLAGS = (IOK,pIOK) IV = 23 NV = 0 PV = 0 {"foo":"23"} {"foo":23} {"foo":23} {"foo":"23"} {"foo":23}
All the available parsers and loaders for Perl are behaving differently, and more important, aren't conforming to the spec. YAML::XS is doing pretty well, but libyaml only handles YAML 1.1 and diverges a bit from the spec. The pure perl loaders lack support for a number of features.
libyaml
I was going over YAML.pm issues end of 216, integrating old patches from rt.cpan.org and creating some pull requests myself. I realized that it would be difficult to patch YAML.pm to parse YAML 1.1 or even 1.2, and it would also break existing usages relying on the current behaviour.
In 2016 Ingy döt Net initiated two really cool projects:
These projects are a big help for any developer. So I got the idea to write my own parser and started on New Year's Day 2017. Without the test suite and the editor I would have never started this.
I also started another YAML Test project which allows to get a quick overview of which frameworks support which YAML features:
https://github.com/yaml/yaml-test-suite
It contains about 230 test cases and expected parsing events and more. There will be more tests coming. This test suite allows to write parsers without turning the examples from the Specification into tests yourself. Also the examples aren't completely covering all cases - the test suite aims to do that.
The suite contains .tml files, and in a seperate 'data' branch you will find the content in seperate files, if you can't or don't want to use TestML.
Thanks also to Felix Krause, who is writing a YAML parser in Nim. He turned all the spec examples into test cases.
This is a tool to play around with several YAML parsers and loaders in vim.
https://github.com/yaml/yaml-editor
The project contains the code to build the frameworks (16 as of this writing) and put it into one big Docker image.
It also contains the yaml-editor itself, which will start a vim in the docker container. It uses a lot of funky vimscript that makes playing with it easy and useful. You can choose which frameworks you want to test and see the output in a grid of vim windows.
Especially when writing a parser it is extremely helpful to have all the test cases and be able to play around with your own examples to see how they are handled.
I was curious to see how the different frameworks handle the test cases, so, using the test suite and the docker image, I wrote some code that runs the tests, manipulates the output to compare it with the expected output, and created a matrix view.
https://github.com/perlpunk/yaml-test-matrix
You can find the latest build at http://matrix.yaml.io
As of this writing, the test matrix only contains valid test cases. Invalid ones will be added.
Copyright 2017 by Tina Müller
This library is free software and may be distributed under the same terms as perl itself.
To install YAML::PP, copy and paste the appropriate command in to your terminal.
cpanm
cpanm YAML::PP
CPAN shell
perl -MCPAN -e shell install YAML::PP
For more information on module installation, please visit the detailed CPAN module installation guide.