yaml

YAML Example

A standalone YAML parser built directly on BaseParser and a custom YAMLLexer subclass. Mirrors the structure of the json/ example.

What it parses

A useful subset of YAML 1.2:

Feature	Example
Block mapping	key: value
Nested block mapping	parent:\n child: val
Block sequence	- item
Flow mapping	{k: v, k2: v2}
Flow sequence	[a, b, c]
Quoted string	"hello world"
Bare-word scalar	hello
Integer	42
Float	3.14
Boolean	true / yes / on (case-insensitive)
Null	null / ~

Architecture

File	Role
yamllexer.h/cpp	YAMLLexer — extends LexicalAnalyzer; manages the INDENT/DEDENT stack and emits the TV_KEY token for mapping keys
yamlvalue.h/cpp	YAMLValue — variant node type (Null, Bool, Int, Float, String, Sequence, Mapping)
yamlparser.h/cpp	YAMLParser — recursive-descent parser; Do*() methods mirror the grammar rules
yaml.cpp	Driver: opens a file, calls parseFile(), dumps the result
test.yaml	Demo input covering all supported features

KEY token trick

YAML block mappings are LL(2) if bare-word keys share the SCALAR token with plain-scalar values, because the parser cannot decide which production to use without looking two tokens ahead. YAMLLexer resolves this by emitting TV_KEY (not TV_SCALAR) when a bare word is immediately followed by : in block context, making the grammar unambiguously LL(1).

Building

Copy or symlink the library headers/sources into the project, then:

c++ -std=c++11 yaml.cpp yamlparser.cpp yamllexer.cpp yamlvalue.cpp \
    ../../lexer.cpp ../../baseparser.cpp ../../symboltable.cpp \
    -o yaml

Running

./yaml test.yaml        # parse and print the value tree
./yaml test.yaml -v     # verbose: trace rule calls

Known limitations

• Only double-quoted strings; single-quoted and block scalars are not handled.
• Only decimal integers; hex (0x…) is not recognised.
• No anchors (&), aliases (*), or tags (!).
• No multi-document streams (--- / ...).