focal (3) YAML::PP.3pm.gz

Provided by: libyaml-pp-perl_0.021-1_all bug

NAME

       YAML::PP - YAML 1.2 processor

SYNOPSIS

       WARNING: Most of the inner API is not stable yet.

       Here are a few examples of the basic load and dump methods:

           use YAML::PP;
           my $ypp = YAML::PP->new;
           my $yaml = <<'EOM';
           --- # Document one is a mapping
           name: Tina
           age: 29
           favourite language: Perl

           --- # Document two is a sequence
           - plain string
           - 'in single quotes'
           - "in double quotes we have escapes! like \t and \n"
           - | # a literal block scalar
             line1
             line2
           - > # a folded block scalar
             this is all one
             single line because the
             linebreaks will be folded
           EOM

           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 @documents = LoadFile($filehandle);
           my $yaml = = Dump(@documents);
           DumpFile($filename, @documents);
           DumpFile($filenhandle @documents);

           my $ypp = YAML::PP->new(schema => [qw/ + Perl /]);
           my $yaml = $yp->dump_string($data_with_perl_objects);

       Some utility scripts, mostly useful for debugging:

           # 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

           # Parse and emit events directly without loading
           yamlpp5-parse-emit < file.yaml

           # Create ANSI colored YAML. Can also be useful for invalid YAML, showing
           # you the exact location of the error
           yamlpp5-highlight < file.yaml

DESCRIPTION

       YAML::PP is a modular YAML processor.

       It aims to support "YAML 1.2" and "YAML 1.1". See <http://yaml.org/>.  Some (rare) syntax elements are
       not yet supported and documented below.

       YAML is a serialization language. The YAML input is called "YAML Stream".  A stream consists of one or
       more "Documents", separated by a line with a document start marker "---". A document optionally ends with
       the document end marker "...".

       This allows one to process continuous streams additionally to a fixed input file or string.

       The YAML::PP frontend will currently load all documents, and return only the first if called with scalar
       context.

       The YAML backend is implemented in a modular way that allows one to add custom handling of YAML tags,
       perl objects and data types. The inner API is not yet stable. Suggestions welcome.

       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>

PLUGINS

       You can alter the behaviour of YAML::PP by using the following schema classes:

       YAML::PP::Schema::Failsafe
           One of the three YAML 1.2 official schemas

       YAML::PP::Schema::JSON
           One of the three YAML 1.2 official schemas.

       YAML::PP::Schema::Core
           One of the three YAML 1.2 official schemas. Default

       YAML::PP::Schema::YAML1_1
           Schema implementing the most common YAML 1.1 types

       YAML::PP::Schema::Perl
           Serializing Perl objects and types

       YAML::PP::Schema::Binary
           Serializing binary data

       YAML::PP::Schema::Tie::IxHash
           Deprecated. See option "preserve"

       YAML::PP::Schema::Merge
           YAML 1.1 merge keys for mappings

       YAML::PP::Schema::Include
           Include other YAML files via "!include" tags

       To make the parsing process faster, you can plugin the libyaml parser with YAML::PP::LibYAML.

IMPLEMENTATION

       The process of loading and dumping is split into the following steps:

           Load:

           YAML Stream        Tokens        Event List        Data Structure
                     --------->    --------->        --------->
                       lex           parse           construct

           Dump:

           Data Structure       Event List        YAML Stream
                       --------->        --------->
                       represent           emit

       You can dump basic perl types like hashes, arrays, scalars (strings, numbers).  For dumping blessed
       objects and things like coderefs have a look at YAML::PP::Perl/YAML::PP::Schema::Perl.

       YAML::PP::Lexer
           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.

       YAML::PP::Parser
           The Parser retrieves the tokens from the Lexer. The main YAML content is then parsed with the
           Grammar.

       YAML::PP::Grammar
       YAML::PP::Constructor
           The Constructor creates a data structure from the Parser events.

       YAML::PP::Loader
           The Loader combines the constructor and parser.

       YAML::PP::Dumper
           The Dumper will delegate to the Representer

       YAML::PP::Representer
           The Representer will create Emitter events from the given data structure.

       YAML::PP::Emitter
           The Emitter creates a YAML stream.

   YAML::PP::Parser
       Still TODO:

       Implicit collection keys
               ---
               [ a, b, c ]: value

       Implicit mapping in flow style sequences
               ---
               [ a, b, c: d ]
               # equals
               [ a, b, { c: d } ]

       Plain mapping keys ending with colons
               ---
               key ends with two colons::: value

       Supported Characters
           If you have valid YAML that's not parsed, or the other way round, please create an issue.

       Line and Column Numbers
           You will see line and column numbers in the error message. The column numbers might still be wrong in
           some cases.

       Error Messages
           The error messages need to be improved.

       Unicode Surrogate Pairs
           Currently loaded as single characters without validating

       Possibly more

   YAML::PP::Constructor
       The Constructor now supports all three YAML 1.2 Schemas, Failsafe, JSON and JSON.  Additionally you can
       choose the schema for YAML 1.1 as "YAML1_1".

       Too see what strings are resolved as booleans, numbers, null etc. look at "t/31.schema.t".

       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'

       The Tags "!!seq" and "!!map" are still ignored for now.

       It supports:

       Handling of Anchors/Aliases
           Like in modules like YAML, the Constructor will use references for mappings and sequences, but
           obviously not for scalars.

       Boolean Handling
           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.

       Numbers
           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.

       Complex Keys
           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)".

           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
                  }
               }

       TODO:

       Parse Tree
           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.

   YAML::PP::Dumper, YAML::PP::Emitter
       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.

       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.

       Numbers which also have a PV flag will be recognized as numbers and not as strings:

           my $int = 23;
           say "int: $int"; # $int will now also have a PV flag

       That means that if you accidentally use a string in numeric context, it will also be recognized as a
       number:

           my $string = "23";
           my $something = $string + 0;
           print $yp->dump_string($string);
           # will be emitted as an integer without quotes!

       The layout is like libyaml output:

           key:
           - a
           - b
           - c
           ---
           - key1: 1
             key2: 2
             key3: 3
           ---
           - - a1
             - a2
           - - b1
             - b2

METHODS

       new
               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' );

               my $ypp = YAML::PP->new(
                   boolean => 'JSON::PP',
                   schema => ['Core'],
                   cyclic_refs => 'fatal',
                   indent => 4,
                   header => 1,
                   footer => 1,
                   version_directive => 1,
               );

           Options:

           boolean
               Values: "perl" (currently default), "JSON::PP", "boolean"

           schema
               Default: "['Core']"

               Array reference. Here you can define what schema to use.  Supported standard Schemas are:
               "Failsafe", "JSON", "Core", "YAML1_1".

               To get an overview how the different Schemas behave, see
               <https://perlpunk.github.io/YAML-PP-p5/schemas.html>

               Additionally you can add further schemas, for example "Merge".

           cyclic_refs
               Default: 'allow' but will be switched to fatal in the future for safety!

               Defines what to do when a cyclic reference is detected when loading.

                   # fatal  - die
                   # warn   - Just warn about them and replace with undef
                   # ignore - replace with undef
                   # allow  - Default

           indent
               Default: 2

               Use that many spaces for indenting

           header
               Default: 1

               Print document heaader "---"

           footer
               Default: 0

               Print document footer "..."

           yaml_version
               Default: 1.2

               Note that in this case, a directive "%YAML 1.1" will basically be ignored and everything loaded
               with the "1.2 Core" Schema.

               If you want to support both YAML 1.1 and 1.2, you have to specify that, and the schema ("Core" or
               "YAML1_1") will be chosen automatically.

                   my $yp = YAML::PP->new(
                       yaml_version => ['1.2', '1.1'],
                   );

               This is the same as

                   my $yp = YAML::PP->new(
                       schema => ['+'],
                       yaml_version => ['1.2', '1.1'],
                   );

               because the "+" stands for the default schema per version.

               When loading, and there is no %YAML directive, 1.2 will be considered as default, and the "Core"
               schema will be used.

               If there is a "%YAML 1.1" directive, the "YAML1_1" schema will be used.

               Of course, you can also make 1.1 the default:

                   my $yp = YAML::PP->new(
                       yaml_version => ['1.1', '1.2'],
                   );

               You can also specify 1.1 only:

                   my $yp = YAML::PP->new(
                       yaml_version => ['1.1'],
                   );

               In this case also documents with "%YAML 1.2" will be loaded with the "YAML1_1" schema.

           version_directive
               Default: 0

               Print Version Directive "%YAML 1.2" (or "%YAML 1.1") on top of each YAML document. It will use
               the first version specified in the "yaml_version" option.

           preserve (since 0.021)
               Experimental. Default: false

                   use YAML::PP::Common qw/ PRESERVE_ORDER PRESERVE_SCALAR_STYLE /;
                   # Preserve the order of hash keys
                   my $yp = YAML::PP->new( preserve => PRESERVE_ORDER );
                   # Preserve the quoting style of scalars
                   my $yp = YAML::PP->new( preserve => PRESERVE_SCALAR_STYLE );
                   # Preserve order and scalar style
                   my $yp = YAML::PP->new( preserve => PRESERVE_ORDER | PRESERVE_SCALAR_STYLE );

               Do NOT rely on the internal implementation of it.

               If you load the following input:

                   ---
                   z: 1
                   a: 2
                   ---
                   - plain
                   - 'single'
                   - "double"
                   - |
                     literal

                   my $yp = YAML::PP->new( preserve => PRESERVE_ORDER | PRESERVE_SCALAR_STYLE );
                   my ($hash, $styles) = $yp->load_file($file);

               Then dumping it will return the same output.  Only folded block scalars '>' cannot preserve the
               style yet.

               When loading, hashes will be tied to an internal class ("YAML::PP::Preserve::Hash") that keeps
               the key order.

               Scalars will be returned as objects of an internal class ("YAML::PP::Preserve::Scalar") with
               overloading. If you assign to such a scalar, the object will be replaced by a simple scalar.

                   # assignment, style gets lost
                   $styles->[1] .= ' append';

       load_string
               my $doc = $ypp->load_string("foo: bar");
               my @docs = $ypp->load_string("foo: bar\n---\n- a");

           Input should be Unicode characters.

           So if you read from a file, you should decode it, for example with "Encode::decode()".

           Note that in scalar context, "load_string" and "load_file" return the first document (like
           YAML::Syck), while YAML and YAML::XS return the last.

       load_file
               my $doc = $ypp->load_file("file.yaml");
               my @docs = $ypp->load_file("file.yaml");

           Strings will be loaded as unicode characters.

       dump_string
               my $yaml = $ypp->dump_string($doc);
               my $yaml = $ypp->dump_string($doc1, $doc2);
               my $yaml = $ypp->dump_string(@docs);

           Input strings should be Unicode characters.

           Output will return Unicode characters.

           So if you want to write that to a file (or pass to YAML::XS, for example), you typically encode it
           via "Encode::encode()".

       dump_file
               $ypp->dump_file("file.yaml", $doc);
               $ypp->dump_file("file.yaml", $doc1, $doc2);
               $ypp->dump_file("file.yaml", @docs);

           Input data should be Unicode characters.

       dump
           This will dump to a predefined writer. By default it will just use the YAML::PP::Writer and output a
           string.

               my $writer = MyWriter->new(\my $output);
               my $yp = YAML::PP->new(
                   writer => $writer,
               );
               $yp->dump($data);

       loader
           Returns or sets the loader object, by default YAML::PP::Loader

       dumper
           Returns or sets the dumper object, by default YAML::PP::Dumper

       schema
           Returns or sets the schema object

       default_schema
           Creates and returns the default schema

FUNCTIONS

       The functions "Load", "LoadFile", "Dump" and "DumpFile" are provided as a drop-in replacement for other
       existing YAML processors.  No function is exported by default.

       Note that in scalar context, "Load" and "LoadFile" return the first document (like YAML::Syck), while
       YAML and YAML::XS return the last.

       Load
               use YAML::PP qw/ Load /;
               my $doc = Load($yaml);
               my @docs = Load($yaml);

           Works like "load_string".

       LoadFile
               use YAML::PP qw/ LoadFile /;
               my $doc = LoadFile($file);
               my @docs = LoadFile($file);
               my @docs = LoadFile($filehandle);

           Works like "load_file".

       Dump
               use YAML::PP qw/ Dump /;
               my $yaml = Dump($doc);
               my $yaml = Dump(@docs);

           Works like "dump_string".

       DumpFile
               use YAML::PP qw/ DumpFile /;
               DumpFile($file, $doc);
               DumpFile($file, @docs);
               DumpFile($filehandle, @docs);

           Works like "dump_file".

NUMBERS

       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}

WHY

       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.

       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:

       "YAML TEST SUITE"
       "YAML EDITOR"

       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 one to get a quick overview of which frameworks
       support which YAML features:

       "YAML TEST MATRIX"

   YAML TEST SUITE
       <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 you 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 separate 'data' branch you will find the content in separate
       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.

   YAML EDITOR
       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.

   YAML TEST MATRIX
       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.

CONTRIBUTORS

       Ingy döt Net
           Ingy is one of the creators of YAML. In 2016 he started the YAML Test Suite and the YAML Editor. He
           also made useful suggestions on the class hierarchy of YAML::PP.

       Felix "flyx" Krause
           Felix answered countless questions about the YAML Specification.

SEE ALSO

       YAML
       YAML::XS
       YAML::Syck
       YAML::Tiny

SPONSORS

       The Perl Foundation <https://www.perlfoundation.org/> sponsored this project (and the YAML Test Suite)
       with a grant of 2500 USD in 2017-2018.

       Copyright 2018 by Tina Müller

       This library is free software and may be distributed under the same terms as perl itself.