Parséman

https://matthew-dean.github.io/parseman/
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Parséman is a 100% pure parser-combinator library for TypeScript that allows developers to write...
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### Install Parséman

Source: https://matthew-dean.github.io/parseman/guide/getting-started

Commands to install the library using common package managers.

```bash
npm install parseman
```

```bash
pnpm add parseman
```

```bash
yarn add parseman
```

--------------------------------

### Define and Run a Parser

Source: https://matthew-dean.github.io/parseman/guide/getting-started

Example of creating an HTTP request line parser using combinators like choice, sequence, and transform.

```ts
import { literal, sequence, choice, regex, transform, parse } from 'parseman'

const method  = choice(literal('GET'), literal('POST'), literal('PUT'), literal('DELETE'))
const target  = regex(/[^\s]+/)
const version = regex(/1\.[01]/)

const requestLine = transform(
  sequence(method, literal(' '), target, literal(' HTTP/'), version),
  ([verb, , path, , ver]) => ({ verb, path, version: `HTTP/${ver}` })
)

parse(requestLine, 'GET /api/v1 HTTP/1.1')
// { ok: true, value: { verb: 'GET', path: '/api/v1', version: 'HTTP/1.1' }, span: … }
```

--------------------------------

### Configure CST Build Host

Source: https://matthew-dean.github.io/parseman/reference/api

Examples of using the generic CST host for structural node grammars, either with default settings or with specific collapse configurations.

```typescript
run(rule, input, { build: cstBuildHost })
```

```typescript
run(rule, input, { build: cstBuildHost({ collapse: ['SelectorList'] }) })
```

--------------------------------

### Parse behavior with expect

Source: https://matthew-dean.github.io/parseman/guide/error-recovery

Examples showing how expect handles valid and invalid input scenarios.

```typescript
// "{ a: 1 }"  →  parses normally; expect(literal('}')) matches, contributes '}'.
```

```typescript
// "{ a: 1"    →  declList consumes "a: 1", then expect(literal('}')) fails.
//               Instead of aborting, it records:
//                 { _tag: 'parseError', span: { start: 6, end: 6 }, expected: ['}'] }
//               and returns a zero-width success. The block node is still produced.
```

--------------------------------

### Scanning with scanTo and balanced

Source: https://matthew-dean.github.io/parseman/guide/combinators

Examples of scanning text until a sentinel or matching balanced delimiters.

```typescript
// [verify]
import { scanTo, balanced, regex, parse } from 'parseman'

parse(scanTo(regex(/[;}]/)), 'a b c; rest').value
// → 'a b c'

parse(balanced('(', ')'), '(a (b) c) rest').value
// → '(a (b) c)'

// The instructive failure: without a sentinel the scan fails, rather than
// silently consuming everything — unless you ask for `orEOF`.
parse(scanTo(regex(/;/)), 'no terminator').ok
// → false
parse(scanTo(regex(/;/), { orEOF: true }), 'no terminator').value
// → 'no terminator'
```

--------------------------------

### Configuring gating behavior in compile()

Source: https://matthew-dean.github.io/parseman/guide/first-char-gating

Examples of how to configure the gating diagnostic behavior during the compilation process.

```typescript
compile(grammar)                        // default: 'warn'
compile(grammar, undefined, { gating: 'off' })    // silence entirely
compile(grammar, undefined, { gating: 'error' })  // fail the build (CI)
const report = compile(grammar).gating  // programmatic GatingReport for snapshots
```

--------------------------------

### Install trivia for a single combinator

Source: https://matthew-dean.github.io/parseman/guide/trivia

Use parser() to apply trivia settings to a specific combinator or standalone parser.

```typescript
import { parser, regex, trivia, sepBy, literal } from 'parseman'

const ws   = trivia(regex(/\s*/))
const list = parser({ trivia: ws }, sepBy(regex(/[a-z]+/), literal(',')))

list.parse('foo ,  bar , baz')   // { ok: true, value: ['foo','bar','baz'], … }
```

--------------------------------

### Install trivia for a whole grammar

Source: https://matthew-dean.github.io/parseman/guide/trivia

Use rules() to set ambient trivia that applies to all terms within the grammar scope.

```typescript
import { rules, sequence, sepBy, choice, literal, regex, trivia, oneOrMore, run } from 'parseman'

const rw = trivia(oneOrMore(regex(/\s+/)))

const g = rules({ trivia: rw }, (r) => ({
  List:  sequence(literal('['), r.items, literal(']')),
  items: sepBy(r.value, literal(',')),
  value: choice(r.List, regex(/[a-z]+/)),
}))

run(g.List, '[ a , [ b , c ] ]')   // spaces skipped between every term
run(g.value, '  a')                // …and when you parse one rule on its own
```

--------------------------------

### Standard JSON module import

Source: https://matthew-dean.github.io/parseman/guide/macro-mode

Example of standard JavaScript import attribute syntax used for JSON modules.

```typescript
import data from './config.json' with { type: 'json' }
```

--------------------------------

### Shared prefix detection patterns

Source: https://matthew-dean.github.io/parseman/guide/natural-grammars

Examples of various structures that Parséman can peer through to identify shared leading terms.

```typescript
choice(sequence(regex(/::?/), a), sequence(regex(/::?/), b))                 // bare
choice(node('A', sequence(regex(/::?/), a), rA), node('B', sequence(regex(/::?/), b), rB))
choice(node('A', parser({ trivia }, sequence(regex(/::?/), a)), rA),        // node + trivia
       node('B', parser({ trivia }, sequence(regex(/::?/), b)), rB))
choice(transform(sequence(literal('--'), a), fA), sequence(literal('--'), b))
```

--------------------------------

### CST Node Structure Example

Source: https://matthew-dean.github.io/parseman/guide/ast

Represents the structure of a CST node with children and leaf nodes.

```typescript
{
  _tag: 'node', type: 'Expr', span: { start: 0, end: 5 }, state: null,
  children: [
    { _tag: 'node', type: 'Num', span: { start: 0, end: 1 }, state: null,
      children: [{ _tag: 'leaf', value: '1', span: { start: 0, end: 1 } }] },
    { _tag: 'leaf', value: '+', span: { start: 2, end: 3 } },
    { _tag: 'node', type: 'Num', span: { start: 4, end: 5 }, state: null,
      children: [{ _tag: 'leaf', value: '2', span: { start: 4, end: 5 } }] },
  ],
}
```

--------------------------------

### Run full benchmark suite

Source: https://matthew-dean.github.io/parseman/guide/benchmarks

Executes the complete performance comparison suite across all supported grammars and input sizes.

```bash
pnpm bench
```

--------------------------------

### Benchmark and Performance Commands

Source: https://matthew-dean.github.io/parseman/guide/performance

A collection of CLI commands for running parser benchmarks, generating regression reports, and checking performance regressions.

```bash
pnpm bench                  # parser-to-parser comparison
pnpm bench:parseman         # Parseman interpreted vs compiled regression report
pnpm bench:svg              # chart-only benchmarks + regenerate assets/bench-*.svg
pnpm bench:baseline         # refresh the regression baseline + append a history snapshot
pnpm bench:release-compare-svg # regenerate committed 0.26/0.27/0.28 release evidence SVGs
pnpm bench:compile-grammars # regenerate the precompiled Peggy/Nearley/Jison parsers
pnpm perf:guard             # fast pre-commit CSS speed regression check

node --import tsx bench/compose-dispatch.ts   # composed-grammar first-char dispatch A/B
```

--------------------------------

### Configuring Grammar for AST and CST Compilation

Source: https://matthew-dean.github.io/parseman/guide/ast

Demonstrates how to define a grammar once and compile it into two separate artifacts for AST and CST consumers using hostMode.

```typescript
const factory = (g) => ({ /* … the whole grammar, written once … */ })

export const grammar    = rules({ trivia: rw }, factory)                    // eval AST
export const cstGrammar = rules({ trivia: rw, hostMode: 'cst' }, factory)   // positioned CST
```

--------------------------------

### Fallback to native regex engine

Source: https://matthew-dean.github.io/parseman/guide/regex-lowering

Example of a pattern that cannot be lowered and remains on the regex engine as a sticky regex.

```javascript
const _re0 = /\S+/y
// …
_re0.lastIndex = _pos
const _m0 = _re0.exec(input)
if (_m0 === null) { /* fail */ }
```

--------------------------------

### Initialize and Edit a Document

Source: https://matthew-dean.github.io/parseman/guide/incremental

Create an incremental document using a registry and root rule, then apply edits using byte offsets.

```typescript
import { parseDoc } from 'parseman'

const registry = { Expr, Num }              // straight from rules()
let doc = parseDoc(registry, 'Expr', src)

doc.tree    // your Node root, or null on failure
doc.errors  // ParseFail[], empty on success
doc.input   // the source string

// edit(from, to, replacement) — two byte offsets into the OLD text + the
// replacement. "Select from→to, type replacement" — the three things every
// editor knows on each keystroke. Returns a NEW doc; the old one is untouched.
doc = doc.edit(changeStart, changeStart + changeLength, newText)
```

--------------------------------

### run(entry, input, options)

Source: https://matthew-dean.github.io/parseman/reference/api

Executes a parser on the provided input. When tolerant mode is enabled, the parser attempts to recover from errors within lists by skipping to inferred sync points.

```APIDOC
## run(entry, input, options)

### Description
Executes the parser defined by `entry` against the `input` string. The `tolerant` option enables list recovery, allowing the parser to continue after encountering errors in `many`, `oneOrMore`, or `sepBy` combinators.

### Parameters
- **entry** (Parser) - Required - The grammar entry point.
- **input** (string) - Required - The input text to parse.
- **options** (object) - Optional - Configuration object.
  - **tolerant** (boolean) - Optional - If true, activates list recovery mode.
```

--------------------------------

### walk(root, visitor, ctx?)

Source: https://matthew-dean.github.io/parseman/guide/ast

Performs a depth-first traversal of the AST with enter and leave hooks. Returning false from the enter hook allows skipping a subtree.

```APIDOC
## walk(root, visitor, ctx?)

### Description
Performs a depth-first traversal of the AST. Users can provide enter and leave hooks to process nodes. Returning false from the enter hook skips the current subtree.

### Signature
`walk<T>(root: T, visitor: { enter?: (node: T) => boolean | void, leave?: (node: T) => void }, ctx?: any)`

### Example
```typescript
import { walk } from 'parseman'

const leaves: string[] = []
walk(tree, {
  enter(node) {
    if (node._tag === 'leaf') leaves.push(node.value)
  },
})
```
```

--------------------------------

### run(entry, input, opts?)

Source: https://matthew-dean.github.io/parseman/reference/api

Executes a grammar entry against the input, managing context such as trivia logs and grammar state.

```APIDOC
## run(entry, input, opts?)

### Description
Runs a grammar entry (a rule function or interpreter combinator) against the input. It threads the standard context and returns a RunResult.

### Parameters
- **entry** (any) - The grammar rule or combinator to run.
- **input** (string) - The input string to process.
- **opts** (object) - Optional configuration.
  - **build** (any) - The CST host.
  - **state** (any) - Initial grammar state.
  - **trivia** (any) - The grammar's trivia rule to skip whitespace/comments.

### Example
```ts
const g = compose([base])
run(g.Value, '12  ', { trivia: g.rw })
```
```

--------------------------------

### Handle Invalid Combinator Input

Source: https://matthew-dean.github.io/parseman/guide/grammar-duplication

Example of the error message thrown when passing a compiled artifact instead of a rules map to the analyzer.

```text
analyzeDuplicationRules: rule 'Declaration' is not a combinator (no _def).
This analysis walks the COMBINATOR TREE; the value returned by compose()/composeLeaf()
is a fused, already-compiled artifact whose entries are parse functions. Pass the
rules() map itself …
```

--------------------------------

### cstBuildHost(opts?)

Source: https://matthew-dean.github.io/parseman/reference/api

Provides a generic CST host for structural node grammars, allowing configuration of node collapsing behavior.

```APIDOC
## cstBuildHost(opts?)

### Description
Returns a host function for `run()` that produces uniform positioned CST nodes. It supports collapsing transparent one-child wrappers.

### Parameters
- **opts** (object) - Optional - Configuration object.
  - **collapse** (boolean | string[] | CstCollapsePredicate) - Defines which nodes to collapse during CST construction.
```

--------------------------------

### Development Commands

Source: https://matthew-dean.github.io/parseman/guide/getting-started

Common scripts for developing and testing the Parséman library.

```bash
pnpm install
pnpm test        # Vitest — interpreter + compiler parity + ordered-choice semantics
pnpm typecheck   # TypeScript 7
pnpm build       # ESM + CJS + .d.ts → dist/
pnpm bench       # vs Peggy, Parsimmon, Chevrotain, Nearley, Jison
pnpm docs:dev    # this documentation site
```

--------------------------------

### walk(root, visitor, ctx?)

Source: https://matthew-dean.github.io/parseman/reference/api

Performs a depth-first traversal of the tree. Calls visitor.enter before children and visitor.leave after children.

```APIDOC
## walk(root, visitor, ctx?)

### Description
Performs a depth-first traversal of the tree. Calls `visitor.enter(node, parent, ctx)` before a node's children and `visitor.leave(node, parent, ctx)` after. Return `false` from `enter` to skip that node's subtree.

### Parameters
- **root** (any) - The root node of the tree.
- **visitor** (object) - An object containing `enter` and `leave` hook functions.
- **ctx** (any) - Optional context object threaded through the traversal.
```

--------------------------------

### parseDoc(registry, rootRule, src, options?)

Source: https://matthew-dean.github.io/parseman/guide/incremental

Initializes a new incremental document instance.

```APIDOC
## parseDoc(registry, rootRule, src, options?)

### Description
Creates a new incremental document instance from a registry of rules and source text.

### Parameters
- **registry** (object) - Required - The object returned by rules() containing parser functions.
- **rootRule** (string) - Required - The name of the entry in the registry to parse from.
- **src** (string) - Required - The source text to parse.
- **options** (object) - Optional - Configuration options, such as { structuralReuse: boolean }.

### Response
- **doc** (object) - An incremental document instance containing the tree, errors, and input.
```

--------------------------------

### Swap output tree shapes with build hosts

Source: https://matthew-dean.github.io/parseman/guide/extending

Use a build host to switch between AST and CST output formats during grammar composition.

```typescript
import { compose, cstBuildHost } from 'parseman'

const parser = compose([base])
parser.Value('12', 0, {})                      // → the grammar's own AST
parser.Value('12', 0, { build: cstBuildHost }) // → a positioned CST node
```

--------------------------------

### toEBNF(grammar, options?)

Source: https://matthew-dean.github.io/parseman/reference/api

Renders a grammar as W3C-style EBNF text.

```APIDOC
## toEBNF(grammar, options?)

### Description
Render W3C-style EBNF text — one production per named rule.

### Parameters
- **grammar** (rules() record or combinator) - Required - The grammar to render.
- **options** (object) - Optional - Includes 'sort', 'root', 'order', 'includeTrivia', 'terminals', and 'regexDisplay'.
```

--------------------------------

### Demonstrate ordered choice behavior

Source: https://matthew-dean.github.io/parseman/guide/keywords

Shows how the order of alternatives affects matching when prefixes are shared.

```typescript
// [verify]
import { choice, literal, regex, parse } from 'parseman'

const op = choice(literal('instanceof'), literal('in'), literal('if'))
parse(op, 'instanceof x').value
// → 'instanceof'

// Short arm first → it matches the prefix and the long arm is unreachable.
const shadowed = choice(regex(/in/), regex(/instanceof/))
parse(shadowed, 'instanceof x').value
// → 'in'
```

--------------------------------

### Create a token with token()

Source: https://matthew-dean.github.io/parseman/reference/api

Wraps a parser to return the matched source text as a single token, collapsing internal CST leaves.

```ts
token(sequence(literal('!'), regex(/important/i)))
```

--------------------------------

### compile(combinator, mapFnSources?)

Source: https://matthew-dean.github.io/parseman/reference/api

JIT-compiles a combinator tree into an optimized JavaScript function at runtime. Returns a CompiledParser object with parsing methods and source metadata.

```APIDOC
## compile(combinator, mapFnSources?)

### Description
JIT-compiles a combinator tree to an optimized JS function at runtime. Requires 'new Function' (won't run under a strict CSP).

### Returns
Returns a `CompiledParser` exposing `.parse()`, `.parseWithContext()`, `.parseWithErrors()`, plus the generated `.source` and `.inlineExpression` strings.
```

--------------------------------

### analyzeGating(entry, opts?)

Source: https://matthew-dean.github.io/parseman/reference/api

Performs a static first-char gating diagnostic over a combinator tree.

```APIDOC
## analyzeGating(entry, opts?)

### Description
Static first-char gating diagnostic over a combinator tree. Returns a `GatingReport` containing findings on gating status, anti-patterns, and deferred choices.

### Parameters
- **entry** (object) - Required - The combinator tree to analyze.
- **opts** (object) - Optional - Configuration options including `accept` (a snapshot allowlist for choice IDs).
```

--------------------------------

### Composing Grammars Across Packages

Source: https://matthew-dean.github.io/parseman/guide/extending

Demonstrates importing a compiled grammar from a base package and extending it within a dialect package.

```typescript
// @scope/base  →  ships a compiled grammar
import { rules, regex, choice } from 'parseman' with { type: 'macro' }
export const base = rules(g => ({ Value: choice(g.Num, g.Word), Num: regex(/[0-9]+/), Word: regex(/[a-z]+/) }))

// @scope/dialect  →  extends it, importing the COMPILED base
import { rules, regex, compose } from 'parseman' with { type: 'macro' }
import { base } from '@scope/base'
export const parser = compose([base, rules(() => ({ Num: regex(/[0-9]+!/) }))])
```

--------------------------------

### parse(c, input, opts?)

Source: https://matthew-dean.github.io/parseman/guide/combinators

Runs a combinator once against the provided input string.

```APIDOC
## parse(c, input, opts?)

### Description
Executes a combinator against an input string. Returns an object containing the result status, the parsed value, and the span of the match.

### Parameters
- **c** (Combinator) - Required - The combinator to execute.
- **input** (string) - Required - The input string to parse.
- **opts** (Object) - Optional - Additional parsing options.
```

--------------------------------

### choice(...alternatives)

Source: https://matthew-dean.github.io/parseman/guide/combinators

Provides ordered alternatives with PEG semantics where the first match wins.

```APIDOC
## choice(...alternatives)

### Description
Ordered alternatives with PEG semantics: first match wins. Write the longer of two overlapping alternatives first to avoid shadowing.
```

--------------------------------

### buildTriviaIndex(root, input?, opts?)

Source: https://matthew-dean.github.io/parseman/reference/api

Walks a CST to generate a lookup table for trivia tokens keyed by node.

```APIDOC
## buildTriviaIndex(root, input?, opts?)

### Description
Converts a flat `triviaLog` into a lookup table of `before` and `after` maps for whitespace-sensitive analysis.

### Parameters
- **root** (object) - Required - The CST root node.
- **input** (string) - Optional - The source input string.
- **opts** (object) - Optional - Additional options for the index build.
```

--------------------------------

### Configure EBNF production ordering

Source: https://matthew-dean.github.io/parseman/guide/spec-generation

Demonstrates how to toggle between declaration order and reachable order when generating EBNF output.

```typescript
// rules declared as [expr, zzz, term], where expr references term:
toEBNF(g)                      // expr, zzz, term   (declaration order)
toEBNF(g, { sort: 'reachable' })  // expr, term, zzz   (term introduced at first use)
```

--------------------------------

### Performance testing commands

Source: https://matthew-dean.github.io/parseman/guide/regex-lowering

Commands used to verify performance and ensure lowering optimizations do not regress.

```bash
pnpm perf:guard      # fast pre-commit check: CSS speed vs a committed baseline
pnpm bench           # parser-to-parser comparison (JSON/CSV/GraphQL)
pnpm bench:parseman  # interpreted vs compiled Parseman suite
pnpm test:perf       # heavier perf assertions
```

--------------------------------

### Run specific benchmark tasks

Source: https://matthew-dean.github.io/parseman/guide/benchmarks

Various commands for regression testing, baseline management, and performance guarding.

```bash
pnpm bench:parseman
```

```bash
pnpm bench:baseline
```

```bash
pnpm perf:guard
```

--------------------------------

### createVisitor(handlers)

Source: https://matthew-dean.github.io/parseman/guide/ast

Creates a visitor function that dispatches based on the node's type. Handlers receive an API object to control recursion.

```APIDOC
## createVisitor(handlers)

### Description
Creates a visitor function that dispatches logic based on the node's type. Handlers receive an API object with `visit` and `visitChildren` methods to manage recursion. If a node type has no handler, it falls through to its children.

### Signature
`createVisitor<R, N>(handlers: { [type: string]: (node: N, api: { visit: (n: N) => R, visitChildren: (n: N) => R[] }) => R }): (root: N) => R`

### Example
```typescript
import { createVisitor } from 'parseman'

const evalExpr = createVisitor<number>({
  Num: (n) => Number((n as NumNode).value),
  Add: (n, api) => api.visitChildren(n).reduce((a, b) => a + b, 0),
})

const total = evalExpr(tree)
```
```

--------------------------------

### Wire language service into a language server

Source: https://matthew-dean.github.io/parseman/guide/editor-integration

Demonstrates managing document state, incremental updates, and completion requests within a language server connection.

```typescript
const css = languageService({ rules: grammar, root: 'StyleSheet' }, config)
const docs = new Map<string, ReturnType<typeof css.openDocument>>()

connection.onDidOpenTextDocument(({ textDocument: t }) => {
  docs.set(t.uri, css.openDocument(t.text))
  publish(t.uri)
})

connection.onDidChangeTextDocument(({ textDocument, contentChanges }) => {
  let doc = docs.get(textDocument.uri)!
  for (const c of contentChanges) {
    const from = doc /* map c.range → offsets */ , to = from // (via your line index)
    doc = doc.edit(from, to, c.text)
  }
  docs.set(textDocument.uri, doc)
  publish(textDocument.uri)
})

connection.onCompletion(({ textDocument, position }) => {
  const doc = docs.get(textDocument.uri)!
  return doc.completionsAt(offsetOf(position)).map(c => ({ label: c.label, detail: c.detail }))
})

function publish(uri: string) {
  const diags = docs.get(uri)!.diagnostics().map(d => ({
    severity: d.severity === 'error' ? 1 : 2,
    range: rangeOf(d.span),
    message: d.message,
  }))
  connection.sendDiagnostics({ uri, diagnostics: diags })
}
```

--------------------------------

### parse(c, input, opts?)

Source: https://matthew-dean.github.io/parseman/guide/combinators

Executes a combinator against an input string using the interpreter.

```APIDOC
## parse(c, input, opts?)

### Description
Runs a combinator once through the interpreter to parse the provided input string.
```

--------------------------------

### Compare grammar performance approaches

Source: https://matthew-dean.github.io/parseman/guide/performance

A comparison of different parsing strategies for a repeated 3-shape group, demonstrating the performance benefits of collapsing combinators into a single regex.

```text
oneOrMore(sequence(ident, sp, num, sp, hex, sp))
```

```text
same, with inline regex(…) instead of shared refs
```

```text
one regex(/…ident…num…hex…/) per group
```

--------------------------------

### Using expect and isParseError

Source: https://matthew-dean.github.io/parseman/guide/combinators

Demonstrates making a token required and checking for parse errors during recovery.

```typescript
// [verify]
import { expect, isParseError, sequence, literal, regex, parse } from 'parseman'

const decl = sequence(regex(/[a-z]+/), expect(literal(':'), 'colon'), regex(/[a-z]*/))
const r = parse(decl, 'color red', { recover: true })

r.ok
// → true
isParseError(r.ok && r.value[1])
// → true
```

--------------------------------

### choice(...args)

Source: https://matthew-dean.github.io/parseman/reference/api

Ordered PEG alternatives where the first match wins. Arms can be plain combinators or gated arms.

```APIDOC
## choice(...args)

### Description
Ordered PEG alternatives where the first match wins. When every arm's first-set is disjoint and non-nullable, the choice compiles to an O(1) first-char dispatch.
```

--------------------------------

### parser(opts, root)

Source: https://matthew-dean.github.io/parseman/reference/api

Wraps a root combinator with document-level options and provides a .parse(input) method.

```APIDOC
## parser(opts, root)

### Description
Wraps a root combinator with document-level options such as `trivia`, `trackLines`, and `captureTrivia`, and adds a `.parse(input)` convenience method.
```

--------------------------------

### Define CstBuildHostOptions

Source: https://matthew-dean.github.io/parseman/reference/types

Configuration for CST construction, including predicates for collapsing transparent wrappers.

```typescript
type CstCollapsePredicate = (
  type: string,
  child: unknown,
  children: readonly unknown[],
  rawChildren: readonly unknown[],
) => boolean

type CstBuildHostOptions = {
  collapse?: boolean | readonly string[] | CstCollapsePredicate
}
```

--------------------------------

### Execute Grammar Instrumentation

Source: https://matthew-dean.github.io/parseman/guide/grammar-observability

Initialize the coverage collector and trace sink, then pass the instrumentation context to the run function.

```typescript
import {
  createGrammarCoverageCollector,
  createGrammarInstrumentationContext,
  createGrammarTraceSink,
  compiledGrammarCoverageDefinitions,
  run,
} from 'parseman'

const collector = createGrammarCoverageCollector(compiledGrammarCoverageDefinitions(grammar))
const trace = createGrammarTraceSink({ capacity: 200 })
const context = createGrammarInstrumentationContext({ collector, trace })

run(grammar.Entry, 'yes', { instrumentation: context })
```

--------------------------------

### Build a visitor with createVisitor

Source: https://matthew-dean.github.io/parseman/reference/api

Creates a visitor that dispatches based on node type, allowing for recursive evaluation of tree structures.

```typescript
const evalExpr = createVisitor<number>({
  Num: (n) => Number((n.children[0] as CSTLeaf).value),
  Add: (n, api) => api.visitChildren(n).reduce((a, b) => a + b, 0),
})

const total = evalExpr(tree)
```

--------------------------------

### Build a CST with a custom host

Source: https://matthew-dean.github.io/parseman/guide/incremental

Pass a build host to ensure that incremental edits produce the same CST structure as a fresh parse.

```typescript
import { parseDoc, cstBuildHost } from 'parseman'

let doc = parseDoc(registry, 'Stylesheet', src, { build: cstBuildHost })
doc = doc.edit(from, to, text)   // re-parsed subtrees are CST nodes too
```

--------------------------------

### Define NodeOptions

Source: https://matthew-dean.github.io/parseman/reference/types

Configuration for AST/CST node construction, including unwrapping, collapsing, and trivia management.

```typescript
type NodeOptions = {
  unwrap?: boolean
  collapse?: boolean
  captureTrivia?: boolean
  trailingTrivia?: boolean // commit one active-trivia run at this node's terminal boundary
}
```

--------------------------------

### Dispatch nodes with createVisitor

Source: https://matthew-dean.github.io/parseman/guide/ast

Dispatches on node types using handlers. Partial visitors are supported as nodes without handlers fall through to children.

```typescript
import { createVisitor } from 'parseman'

const evalExpr = createVisitor<number>({
  Num: (n) => Number((n as NumNode).value),
  Add: (n, api) => api.visitChildren(n).reduce((a, b) => a + b, 0),
})

const total = evalExpr(tree)
```

--------------------------------

### compile(c)

Source: https://matthew-dean.github.io/parseman/guide/combinators

Lowers a combinator to JavaScript for improved performance while maintaining the same semantics.

```APIDOC
## compile(c)

### Description
Compiles a combinator into executable JavaScript code.
```

--------------------------------

### Using the peek combinator

Source: https://matthew-dean.github.io/parseman/guide/combinators

Demonstrates using peek for positive lookahead to check for patterns without consuming them.

```typescript
// [verify]
import { peek, sequence, literal, regex, parse } from 'parseman'

// "only try this arm when the punctuation is ahead" — then let the real
// production consume it.
const mixinRef = sequence(peek(regex(/[.#]/)), regex(/[.#][\w-]+/))

parse(mixinRef, '.rounded').value
// → [null, '.rounded']

parse(mixinRef, 'rounded').ok
// → false

// Zero-width, like `not`.
parse(peek(literal('@')), '@media').span
// → { start: 0, end: 0 }
```

--------------------------------

### makeWord(boundary, options)

Source: https://matthew-dean.github.io/parseman/guide/combinators

Creates a factory function for parsing keywords with specific boundary characters and options.

```APIDOC
## makeWord(boundary, options)

### Description
A definition-time factory that fixes the boundary class and keyword options, for grammars where every keyword shares them.

### Parameters
- **boundary** (string) - Required - A string defining the allowed characters for the word.
- **options** (object) - Optional - Configuration object (e.g., { caseInsensitive: boolean }).
```

--------------------------------

### scanTo(sentinel, opts?)

Source: https://matthew-dean.github.io/parseman/guide/combinators

Walks forward until the sentinel matches without consuming it, returning the skipped text.

```APIDOC
## scanTo(sentinel, opts?)

### Description
Scans input until a sentinel is found. It respects ambient trivia and `scanSkip` configurations.

### Parameters
- **sentinel** (Parser) - Required - The parser to stop at.
- **opts** (Object) - Optional - Configuration options.
  - **skip** (Array) - Extra opaque units to skip.
  - **raw** (boolean) - If true, skips nothing ambiently.
  - **orEOF** (boolean) - If true, succeeds at EOF if sentinel is not found.
```

--------------------------------

### Binding Compiled Rules

Source: https://matthew-dean.github.io/parseman/guide/macro-mode

Demonstrates the two ways to bind compiled rules from a factory.

```typescript
const { value } = rules(…)   // each rule becomes a top-level function
const grammar   = rules(…)   // an object literal of compiled rules; grammar.value(…) works
```

--------------------------------

### analyzeDuplicationRules(ruleMap, opts?)

Source: https://matthew-dean.github.io/parseman/reference/api

Performs a static structural-duplication diagnostic over a rule map.

```APIDOC
## analyzeDuplicationRules(ruleMap, opts?)

### Description
Performs a static structural-duplication diagnostic over a rule map. Reports eight families of findings including rewrites, structure loss, and regex fragments.

### Parameters
- **ruleMap** (Object) - Required - The rules map to analyze.
- **opts** (Object) - Optional - Configuration options.
  - **accept** (Array) - Optional - Allowlist of finding IDs.

### Response
- **DuplicationReport** (Object) - A report containing findings across eight categories.
```

--------------------------------

### Recognizing keywords with word, literal, and regex

Source: https://matthew-dean.github.io/parseman/guide/combinators

Demonstrates how word, literal, and regex combinators handle keyword matching and boundary requirements.

```typescript
// [verify]
import { word, literal, regex, parse } from 'parseman'

const all = (input: string) => [parse(word('if'), input).ok, parse(literal('if'), input).ok, parse(regex(/if/), input).ok]

// All three match `if` at the start…
all('if x')
// → [true, true, true]

// …but only `word` refuses the keyword inside a longer word.
all('ifdef')
// → [false, true, true]
```

--------------------------------

### keywords(words, opts?)

Source: https://matthew-dean.github.io/parseman/reference/api

Matches one of many keywords, compiled to a single sticky regex.

```APIDOC
## keywords(words, opts?)

### Description
Matches one of many keywords, longest-first, compiled to a single sticky regex.

### Parameters
- **words** (string[]) - Required - Array of keywords to match.
- **opts** (object) - Optional - Configuration options including boundary and caseInsensitive.
```

--------------------------------

### dispatch(selector, when(...), otherwise(...))

Source: https://matthew-dean.github.io/parseman/reference/api

Parses a selector once, uses its string value as a static dispatch key, then parses the selected tail.

```APIDOC
## dispatch(selector, when(...), otherwise(...))

### Description
Parse `selector` once, use its string value as a static dispatch key, then parse the selected tail from the selector end. Use this when one broad selector token is valid generally, and selected selector values have specialized continuation grammars.
```

--------------------------------

### Create a word parser with makeWord

Source: https://matthew-dean.github.io/parseman/guide/combinators

Defines a factory for keywords that share specific boundary and case-sensitivity settings.

```typescript
// [verify]
import { makeWord, parse } from 'parseman'

const cssKw = makeWord('A-Za-z0-9_-', { caseInsensitive: true })

parse(cssKw('screen'), 'SCREEN and (x)').value
// → 'SCREEN'
parse(cssKw('screen'), 'screen-only').ok
// → false
```

--------------------------------

### Compile a grammar at runtime

Source: https://matthew-dean.github.io/parseman/guide/modes

Use compile() to generate a parser at runtime when a build step is not feasible. Note that this requires 'unsafe-eval' permissions due to the use of new Function.

```typescript
import { choice, literal, compile } from 'parseman'

const compiled = compile(choice(literal('yes'), literal('no')))
compiled.parse('yes', 0, { trackLines: false }) // { ok: true, value: 'yes', … }
compiled.source                                  // the generated JS source string
compiled.inlineExpression                        // self-contained expr (what the plugin inlines)
```

--------------------------------

### parser(options, root)

Source: https://matthew-dean.github.io/parseman/guide/combinators

Configures a parser with grammar-wide options such as trivia handling.

```APIDOC
## parser(options, root)

### Description
Sets up a parser with specific options. The 'trivia' option defines a combinator to be treated as skippable filler between sequence terms.
```

--------------------------------

### Committing vs looking with attempt and peek

Source: https://matthew-dean.github.io/parseman/guide/combinators

Compares attempt, which consumes input on success, with peek, which is zero-width.

```typescript
// [verify]
import { attempt, peek, literal, parse } from 'parseman'

[parse(attempt(literal('ab')), 'abc').span.end, parse(peek(literal('ab')), 'abc').span.end]
// → [2, 0]
```

--------------------------------

### Update benchmark charts

Source: https://matthew-dean.github.io/parseman/guide/benchmarks

Generates and updates the SVG comparison charts located in the assets directory.

```bash
pnpm bench:svg    # run chart-only benchmarks, then write assets/bench-*.svg
```

--------------------------------

### Execute grammar with the Interpreter mode

Source: https://matthew-dean.github.io/parseman/guide/modes

The default mode requires no build step or configuration, executing directly in any JavaScript environment.

```typescript
import { choice, literal, parse } from 'parseman'

const yesNo = choice(literal('yes'), literal('no'))
parse(yesNo, 'yes') // { ok: true, value: 'yes', … }
```

--------------------------------

### makeWord(boundary?, opts?)

Source: https://matthew-dean.github.io/parseman/reference/api

Returns a factory function that creates a Combinator with a fixed boundary class and keyword options.

```APIDOC
## makeWord(boundary?, opts?)

### Description
Returns a factory function that creates a Combinator with a fixed boundary class and keyword options.

### Parameters
- **boundary** (string) - Optional - Fixed boundary class.
- **opts** (object) - Optional - Keyword options.
```

--------------------------------

### Parse and compile combinators

Source: https://matthew-dean.github.io/parseman/guide/combinators

Demonstrates using parse() for interpretation and compile() for lowering to JavaScript.

```typescript
// [verify]
import { compile, parse, choice, literal } from 'parseman'

const g = choice(literal('a'), literal('b'))
const compiled = compile(g, undefined, { gating: 'off' })

parse(g, 'b').value
// → 'b'
compiled.parse('b').value
// → 'b'
```

--------------------------------

### Assemble a grammar from reusable parts

Source: https://matthew-dean.github.io/parseman/guide/extending

Factor reusable rules into standalone grammar objects and compose them into a host grammar. References within the mixin resolve to the host grammar's definitions at runtime.

```typescript
// A package exports the mixin machinery as a standalone composable grammar…
export const mixins = rules({ trivia }, (g) => ({
  MixinCall: sequence(g.Selector, literal('('), g.args, literal(')')),
  // …references g.Selector / g.args by name — the composing grammar supplies them.
}))

// …and a consumer composes just that piece in:
const parser = compose([css, mixins, myDelta])
```

--------------------------------

### Line Indexing Utilities

Source: https://matthew-dean.github.io/parseman/reference/api

Low-level primitives for mapping byte offsets to line and column information.

```APIDOC
## buildLineIndex(input)
Precomputes newline offsets to create a LineIndex for O(log n) lookups.

## offsetToLineCol(index, offset)
Maps a byte offset to a { line, col } object (1-based).

## annotateSpan(span, index)
Returns a copy of a span with startLine, startColumn, endLine, and endColumn properties filled in.
```

--------------------------------

### scanTo(sentinel, opts?)

Source: https://matthew-dean.github.io/parseman/reference/api

Consumes text until the specified sentinel is reached, while respecting ambient skip rules.

```APIDOC
## scanTo(sentinel, opts?)

### Description
Consumes text up to the sentinel. By default, it skips ambient trivia and opaque units.

### Parameters
- **sentinel** (string) - Required - The text to stop at.
- **opts** (object) - Optional - 
  - **skip** (array) - Optional - Extra opaque regions to skip.
  - **raw** (boolean) - Optional - If true, disables all ambient skipping.
  - **orEOF** (boolean) - Optional - If true, treats EOF as a success.
```

--------------------------------

### Implement CI Gating Allowlist

Source: https://matthew-dean.github.io/parseman/guide/first-char-gating

Use an allowlist to track reviewed ungated choices and fail the build if new ungated choices appear or allowlist entries become stale.

```typescript
import { analyzeGating } from 'parseman'
const ACCEPTED = ['statement', 'value#1']    // reviewed, intentional (keep a reason each)
const report = analyzeGating(grammarEntry, { accept: ACCEPTED })
expect(report.ungated.map(c => c.id)).toEqual([])   // fails when a NEW choice ungates
expect(report.acceptedUnused).toEqual([])           // fails when an allowlist entry goes stale
```

--------------------------------

### Execute a parser with options

Source: https://matthew-dean.github.io/parseman/reference/api

Run a combinator against an input string with specific parsing options enabled.

```typescript
parse(myParser, 'hello world', { trackLines: true, recover: true })
```

--------------------------------

### Configure Vitest for grammar coverage

Source: https://matthew-dean.github.io/parseman/guide/grammar-observability

Enables grammar instrumentation in the Vite configuration for test builds.

```typescript
// vitest.config.ts
import parseman from 'parseman/plugin'

export default {
  plugins: [parseman.vite({ grammarCoverage: true })],
}
```

--------------------------------

### attempt(combinator)

Source: https://matthew-dean.github.io/parseman/reference/api

Makes one ordered-choice arm transactional, restoring state if the parser fails after consuming input.

```APIDOC
## attempt(combinator)

### Description
Make one ordered-choice arm transactional. If its parser fails after consuming input, Parseman restores its structural capture, trivia, field, and recovery diagnostic sinks before returning a zero-width failure at the attempt entry.
```

--------------------------------

### analyzeDuplication(entry, opts?)

Source: https://matthew-dean.github.io/parseman/reference/api

Performs a static structural-duplication diagnostic over a combinator tree entry.

```APIDOC
## analyzeDuplication(entry, opts?)

### Description
Performs a static structural-duplication diagnostic over a combinator tree. Reports eight families of findings including rewrites, structure loss, and regex fragments.

### Parameters
- **entry** (Object) - Required - The rules map to analyze.
- **opts** (Object) - Optional - Configuration options.
  - **accept** (Array) - Optional - Allowlist of finding IDs.

### Response
- **DuplicationReport** (Object) - A report containing findings across eight categories.
```

--------------------------------

### Build Specification Model

Source: https://matthew-dean.github.io/parseman/guide/spec-generation

Generate a notation-agnostic model with specific root rules to control output scope.

```typescript
buildSpecModel(g, { root: 'expr' })   // only expr, call, list
```

--------------------------------

### composeLeaf([...recognition, localRules])

Source: https://matthew-dean.github.io/parseman/reference/api

A macro that fuses imported recognition-only grammar pieces with a final local rules map.

```APIDOC
## composeLeaf([...recognition, localRules])

### Description
Fuses imported, recognition-only grammar pieces with one final local rules() map. This macro is terminal and cannot be fed into another compose or composeLeaf call.

### Parameters
- **recognition** (array) - Required - Array of recognition-only grammar pieces.
- **localRules** (object) - Required - The final local rules map.
```

--------------------------------

### completionsAt(target, input, offset, options?)

Source: https://matthew-dean.github.io/parseman/reference/api

Returns the set of expected tokens at a specific cursor offset, providing the raw material for autocomplete functionality.

```APIDOC
## completionsAt(target, input, offset, options?)

### Description
Returns the set of expected tokens at a cursor offset by probing the grammar at that position via a truncated parse.

### Parameters
- **target** (interpreter combinator or compiled grammar) - Required - The grammar or interpreter to probe.
- **input** (string) - Required - The input text to parse.
- **offset** (number) - Required - The cursor position.
- **options.tolerant** (boolean) - Optional - When true, list recovery keeps parsing past a bad element before the cursor. Default: false.
```

--------------------------------

### Configure Macro build mode

Source: https://matthew-dean.github.io/parseman/guide/modes

Use import attributes to trigger compile-time evaluation of combinators during the build process.

```typescript
import { literal, sequence, choice } from 'parseman' with { type: 'macro' }
```
Tokens:
Raw