Brunobkr/llama.cpp_AlgMor24_github

1# Parsing Model Output2 3The `common` library contains a PEG parser implementation suitable for parsing4model output.5 6Types with the prefix `common_peg_*` are intended for general use and may have7applications beyond parsing model output, such as parsing user-provided regex8patterns.9 10Types with the prefix `common_chat_peg_*` are specialized helpers for model11output.12 13The parser features:14 15- Partial parsing of streaming input16- Built-in JSON parsers17- AST generation with semantics via "tagged" nodes18 19## Example20 21Below is a contrived example demonstrating how to use the PEG parser to parse22output from a model that emits arguments as JSON.23 24```cpp25auto parser = build_chat_peg_parser([&](common_chat_peg_builder & p) {26    // Build a choice of all available tools27    auto tool_choice = p.choice();28    for (const auto & tool : tools) {29        const auto & function = tool.at("function");30        std::string name = function.at("name");31        const auto & schema = function.at("parameters");32 33        auto tool_name = p.json_member("name", "\"" + p.literal(name) + "\"");34        auto tool_args = p.json_member("arguments", p.schema(p.json(), "tool-" + name + "-schema", schema));35 36        tool_choice |= p.rule("tool-" + name, "{" << tool_name << "," << tool_args << "}");37    }38 39    // Define the tool call structure: <tool_call>[{tool}]</tool_call>40    auto tool_call = p.trigger_rule("tool-call",41        p.sequence({42            p.literal("<tool_call>["),43            tool_choice,44            p.literal("]</tool_call>")45        })46    );47 48    // Parser accepts content, optionally followed by a tool call49    return p.sequence({50        p.content(p.until("<tool_call>")),51        p.optional(tool_call),52        p.end()53    });54});55```56 57For a more complete example, see `test_example_native()` in58[tests/test-chat-peg-parser.cpp](/tests/test-chat-peg-parser.cpp).59 60## Parsers/Combinators61 62### Basic Matchers63 64- **`eps()`** - Matches nothing and always succeeds (epsilon/empty match)65- **`start()`** - Matches the start of input (anchor `^`)66- **`end()`** - Matches the end of input (anchor `$`)67- **`literal(string)`** - Matches an exact literal string68- **`any()`** - Matches any single character (`.`)69 70### Combinators71 72- **`sequence(...)`** - Matches parsers in order; all must succeed73- **`choice(...)`** - Matches the first parser that succeeds from alternatives (ordered choice)74- **`one_or_more(p)`** - Matches one or more repetitions (`+`)75- **`zero_or_more(p)`** - Matches zero or more repetitions (`*`)76- **`optional(p)`** - Matches zero or one occurrence (`?`)77- **`repeat(p, min, max)`** - Matches between min and max repetitions (use `-1` for unbounded)78- **`repeat(p, n)`** - Matches exactly n repetitions79 80### Lookahead81 82- **`peek(p)`** - Positive lookahead: succeeds if parser succeeds without consuming input (`&`)83- **`negate(p)`** - Negative lookahead: succeeds if parser fails without consuming input (`!`)84 85### Character Classes & Utilities86 87- **`chars(classes, min, max)`** - Matches repetitions of characters from a character class88- **`space()`** - Matches zero or more whitespace characters (space, tab, newline)89- **`until(delimiter)`** - Matches characters until delimiter is found (delimiter not consumed)90- **`until_one_of(delimiters)`** - Matches characters until any delimiter in the list is found91- **`rest()`** - Matches everything remaining (`.*`)92 93### JSON Parsers94 95- **`json()`** - Complete JSON parser (objects, arrays, strings, numbers, booleans, null)96- **`json_object()`** - JSON object parser97- **`json_array()`** - JSON array parser98- **`json_string()`** - JSON string parser99- **`json_number()`** - JSON number parser100- **`json_bool()`** - JSON boolean parser101- **`json_null()`** - JSON null parser102- **`json_string_content()`** - JSON string content without surrounding quotes103- **`json_member(key, p)`** - JSON object member with specific key and value parser104 105### Grammar Building106 107- **`ref(name)`** - Creates a lightweight reference to a named rule (for recursive grammars)108- **`rule(name, p, trigger)`** - Creates a named rule and returns a reference109- **`trigger_rule(name, p)`** - Creates a trigger rule (entry point for lazy grammar generation)110- **`schema(p, name, schema, raw)`** - Wraps parser with JSON schema metadata for grammar generation111 112### AST Control113 114- **`atomic(p)`** - Prevents AST node creation for partial parses115- **`tag(tag, p)`** - Creates AST nodes with semantic tags (multiple nodes can share tags)116 117## GBNF Grammar Generation118 119The PEG parser also acts as a convenient DSL for generating GBNF grammars, with120some exceptions.121 122```cpp123data.grammar = build_grammar([&](const common_grammar_builder & builder) {124    foreach_function(params.tools, [&](const json & fn) {125        builder.resolve_refs(fn.at("parameters"));126    });127    parser.build_grammar(builder, data.grammar_lazy);128});129```130 131The notable exception is the `negate(p)` lookahead parser, which cannot be132defined as a CFG grammar and therefore does not produce a rule. Its usage133should be limited and preferably hidden behind a `schema()` parser. In many134cases, `until(delimiter)` or `until_one_of(delimiters)` is a better choice.135 136Another limitation is that the PEG parser requires an unambiguous grammar. In137contrast, the `llama-grammar` implementation can support ambiguous grammars,138though they are difficult to parse.139 140### Lazy Grammars141 142During lazy grammar generation, only rules reachable from a `trigger_rule(p)`143are emitted in the grammar. All trigger rules are added as alternations in the144root rule. It is still necessary to define trigger patterns, as the parser has145no interaction with the grammar sampling.146 147### JSON Schema148 149The `schema(p, name, schema, raw)` parser will use the `json-schema-to-grammar`150implementation to generate the grammar instead of the underlying parser.151 152The `raw` option emits a grammar suitable for a raw string instead of a JSON153string. In other words, it won't be wrapped in quotes or require escaping154quotes. It should only be used when `type == "string"`.155 156The downside is that it can potentially lead to ambiguous grammars. For157example, if a user provides the pattern `^.*$`, the following grammar may be158generated:159 160```161root ::= "<arg>" .* "</arg>"162```163 164This creates an ambiguous grammar that cannot be parsed by the PEG parser. To165help mitigate this, if `.*` is found in the pattern, the grammar from the166underlying parser will be emitted instead.167 168## Common AST Shapes for Chat Parsing169 170Most model output can be placed in one of the following categories:171 172- Content only173- Tool calling with arguments emitted as a single JSON object174- Tool calling with arguments emitted as separate entities, either XML175  (Qwen3-Coder, MiniMax M2) or pseudo-function calls (LFM2)176 177To provide broad coverage,178[`common/chat-peg-parser.h`](/common/chat-peg-parser.h) contains builders and179mappers that help create parsers and visitors/extractors for these types. They180require parsers to tag nodes to conform to an AST "shape". This normalization181makes it easy to extract information and generalize parsing.182 183### Simple184 185The `common_chat_peg_builder` builds a `simple` parser that supports186content-only models with optional reasoning.187 188- **`reasoning(p)`** - Tag node for extracting `reasoning_content`189- **`content(p)`** - Tag node for extracting `content`190 191```cpp192build_chat_peg_parser([&](common_chat_peg_parser & p) {193    return p.sequence({194        p.optional("<think>" + p.reasoning(p.until("</think>")) + "</think>"),195        p.content(p.until("<tool_call>")),196        p.end()197    });198});199```200 201Use `common_chat_peg_mapper` to extract the content. Note that this is already202done for you in `common_chat_peg_parser` when203`chat_format == COMMON_CHAT_FORMAT_PEG_SIMPLE`.204 205```cpp206auto result = parser.parse(ctx);207 208common_chat_msg msg;209auto mapper = common_chat_peg_mapper(msg);210mapper.from_ast(ctx.ast, result);211```212 213### Native214 215The `common_chat_peg_builder` builds a `native` parser suitable for216models that emit tool arguments as a direct JSON object.217 218- **`reasoning(p)`** - Tag node for `reasoning_content`219- **`content(p)`** - Tag node for `content`220- **`tool(p)`** - Tag entirety of a single tool call221- **`tool_open(p)`** - Tag start of a tool call222- **`tool_close(p)`** - Tag end of a tool call223- **`tool_id(p)`** - Tag the tool call ID (optional)224- **`tool_name(p)`** - Tag the tool name225- **`tool_args(p)`** - Tag the tool arguments226 227```cpp228build_chat_peg_parser([&](common_chat_peg_builder & p) {229    auto get_weather_tool = p.tool(p.sequence({230        p.tool_open(p.literal("{")),231        p.json_member("name", "\"" + p.tool_name(p.literal("get_weather")) + "\""),232        p.literal(","),233        p.json_member("arguments", p.tool_args(p.json())),234        p.tool_close(p.literal("}"))235    }));236 237    return p.sequence({238        p.content(p.until("<tool_call>")),239        p.literal("<tool_call>"),240        get_weather_tool,241        p.literal("</tool_call>"),242        p.end()243    });244});245```246 247### Constructed248 249The `common_chat_peg_builder` builds a `constructed` parser250suitable for models that emit tool arguments as separate entities, such as XML251tags.252 253- **`reasoning(p)`** - Tag node for `reasoning_content`254- **`content(p)`** - Tag node for `content`255- **`tool(p)`** - Tag entirety of a single tool call256- **`tool_open(p)`** - Tag start of a tool call257- **`tool_close(p)`** - Tag end of a tool call258- **`tool_name(p)`** - Tag the tool name259- **`tool_arg(p)`** - Tag a complete tool argument (name + value)260- **`tool_arg_open(p)`** - Tag start of a tool argument261- **`tool_arg_close(p)`** - Tag end of a tool argument262- **`tool_arg_name(p)`** - Tag the argument name263- **`tool_arg_string_value(p)`** - Tag string value for the argument264- **`tool_arg_json_value(p)`** - Tag JSON value for the argument265 266```cpp267build_chat_peg_parser([&](common_chat_peg_builder & p) {268    auto location_arg = p.tool_arg(269        p.tool_arg_open("<parameter name=\"" + p.tool_arg_name(p.literal("location")) + "\">"),270        p.tool_arg_string_value(p.until("</parameter>")),271        p.tool_arg_close(p.literal("</parameter>"))272    );273 274    auto get_weather_tool = p.tool(p.sequence({275        p.tool_open("<function name=\"" + p.tool_name(p.literal("get_weather")) + "\">"),276        location_arg,277        p.tool_close(p.literal("</function>"))278    }));279 280    return p.sequence({281        p.content(p.until("<tool_call>")),282        p.literal("<tool_call>"),283        get_weather_tool,284        p.literal("</tool_call>"),285        p.end()286    });287});288```289