bobzhang/peg/vm - mooncakes.io

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ActionFn

type ActionFn[T] = (@bobzhang/peg/runtime.ActionContext
ActionContext[T]) -> @bobzhang/peg/runtime.Value
Value[T] raise

Implementation of an action or semantic predicate code block. Predicates return a value whose JavaScript truthiness decides the match.

InitFn

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type InitFn[T] = (@bobzhang/peg/runtime.ActionContext
ActionContext[T]) -> Map[String, (@bobzhang/peg/runtime.ActionContext
ActionContext[T]) -> @bobzhang/peg/runtime.Value
Value[T] raise] raise

Implementation of a grammar's initializer block. It runs once per parse (after the start rule is validated) and returns bindings that take precedence over the statically supplied ones, so actions can share per-parse state by closing over it.

SyntaxError

source

using @bobzhang/peg/runtime { type SyntaxError }

Raised by a parser when the input does not match the grammar, or by the error() / expected() action helpers.

expected and found are None for errors raised through error(), like the null fields of PEG.js' peg$SyntaxError.

Tracer

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using @bobzhang/peg/runtime { type Tracer }

Receives rule enter/match/fail events when tracing is enabled.

Value

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using @bobzhang/peg/runtime { type Value }

A dynamically typed value produced by a PEG.js-style parser.

Mirrors the JavaScript values PEG.js parsers produce: literals, classes and . yield Str, sequences and repetitions yield Arr, ? yields Null on failure and predicates yield Undefined. Custom carries application payloads produced by actions.

UnboundCode

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pub(all) suberror UnboundCode {
  UnboundCode(kind~ : String, code~ : String)
} derive(@moonbitlang/core/debug.Debug
Debug)

Raised when a code block of the grammar has no MoonBit implementation.

impl Show for UnboundCode

Parser

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pub struct Parser[T] {
  program : @bobzhang/peg/bytecode.Program
Program?
  // private fields
}

A generated parser.

Usually built from a compiled Program by Parser::from_program, but any parse function can be wrapped (e.g. by compiler plugins).

Parser::from_fn

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fn[T] Parser::from_fn(parse : (String, Map[String, @bobzhang/peg/runtime.Value
Value[T]], @bobzhang/peg/runtime.Tracer
Tracer[T]?) -> @bobzhang/peg/runtime.Value
Value[T] raise) -> Parser[T]

Wraps a parse function. It receives the input, the parse options (which include startRule / filename when given) and the tracer, if any.

Parser::from_program

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fn[T] Parser::from_program(program : @bobzhang/peg/bytecode.Program
Program, actions? : Map[String, (@bobzhang/peg/runtime.ActionContext
ActionContext[T]) -> @bobzhang/peg/runtime.Value
Value[T] raise], initializer? : (@bobzhang/peg/runtime.ActionContext
ActionContext[T]) -> Map[String, (@bobzhang/peg/runtime.ActionContext
ActionContext[T]) -> @bobzhang/peg/runtime.Value
Value[T] raise] raise) -> Parser[T] raise UnboundCode

Builds a parser interpreting program.

Each action / predicate code block is implemented by the entry of actions keyed by its exact body or trimmed body (see lookup_binding). A grammar initializer requires initializer, which runs per parse and may supply further bindings. Raises UnboundCode for missing bindings (at parse time for bindings the initializer is expected to provide).

Parser::parse

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fn[T] Parser::parse(self : Parser[T], input : String, start_rule? : String, filename? : String, tracer? : @bobzhang/peg/runtime.Tracer
Tracer[T], options? : Map[String, @bobzhang/peg/runtime.Value
Value[T]]) -> @bobzhang/peg/runtime.Value
Value[T] raise

Parses input, returning the start rule's result.

options is exposed to actions as PEG.js' options object; start_rule and filename are shorthands for its startRule and filename entries. Raises @runtime.SyntaxError when the input does not match.

lookup_binding

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fn[V] lookup_binding(bindings : Map[String, V], index : Int, body : String) -> V?

Looks up the implementation of code block number index (its position in Program::functions) with source text body. Keys are tried in order:

"#<index>" — exact, but specific to one compilation of the grammar;
the exact body text;
the body with surrounding whitespace trimmed (so a grammar can simply say { makeNumber }).

Identical bodies with different labels in scope share a text key, so actions bound by text should read labels by name (ActionContext::label).