diff --git a/benchmarks/src/json/index.ts b/benchmarks/src/json/index.ts
index adb672d..f1551b0 100644
--- a/benchmarks/src/json/index.ts
+++ b/benchmarks/src/json/index.ts
@@ -4,12 +4,14 @@ import { handlers } from '../@helpers'
 
 import { SAMPLE } from './@sample'
 import { parse as parseParjs } from './parjs'
-import { parse as parseSigma } from './sigma'
+import { parse as parseSigmaDefer } from './sigma'
+import { parse as parseSigmaGrammar } from './sigma-grammar'
 
 suite(
   'JSON :: sigma vs parjs',
 
-  add('sigma', () => parseSigma(SAMPLE)),
+  add('sigma:defer', () => parseSigmaDefer(SAMPLE)),
+  add('sigma:grammar', () => parseSigmaGrammar(SAMPLE)),
   add('parjs', () => parseParjs(SAMPLE)),
 
   ...handlers
diff --git a/benchmarks/src/json/sigma-grammar.ts b/benchmarks/src/json/sigma-grammar.ts
new file mode 100644
index 0000000..17bfa37
--- /dev/null
+++ b/benchmarks/src/json/sigma-grammar.ts
@@ -0,0 +1,169 @@
+import { choice, sepBy, optional, map, takeMid, sequence } from '@combinators'
+import { Parser } from '@lib'
+import { float, grammar, integer, regexp, run, string, whitespace } from '@parsers'
+
+import * as Ast from './ast'
+
+/* Tokens. */
+
+const Keywords = {
+  True: 'true',
+  False: 'false',
+  Null: 'null'
+} as const
+
+const Terminals = {
+  OpenBrace: '{',
+  CloseBrace: '}',
+  OpenSquare: '[',
+  CloseSquare: ']',
+  Colon: ':',
+  Comma: ','
+} as const
+
+/* Mapping functions to turn parsed string values into AST nodes. */
+
+function toObject(values: Array<Ast.JsonObjectProp>): Ast.JsonObject {
+  return {
+    type: 'object',
+    values
+  }
+}
+
+function toObjectProp(tuple: [Ast.JsonString, string, Ast.JsonValue]): Ast.JsonObjectProp {
+  const [{ value: name }, _, value] = tuple
+
+  return {
+    type: 'property',
+    name,
+    value
+  }
+}
+
+function toArray(values: Array<Ast.JsonValue>): Ast.JsonArray {
+  return {
+    type: 'array',
+    values
+  }
+}
+
+function toString(text: string): Ast.JsonString {
+  return {
+    type: 'string',
+    value: text.slice(1, -1)
+  }
+}
+
+function toNumber(value: number): Ast.JsonNumber {
+  return {
+    type: 'number',
+    value: value
+  }
+}
+
+function toBoolean(kind: string): Ast.JsonBoolean {
+  switch (kind) {
+    case Keywords.True: {
+      return {
+        type: 'boolean',
+        value: true
+      }
+    }
+
+    case Keywords.False: {
+      return {
+        type: 'boolean',
+        value: false
+      }
+    }
+
+    default: {
+      return {
+        type: 'boolean',
+        value: false
+      }
+    }
+  }
+}
+
+function toNull(): Ast.JsonNull {
+  return {
+    type: 'null',
+    value: null
+  }
+}
+
+/* Parsers. */
+
+// Non-Terminals.
+const NumberLiteral = choice(float(), integer())
+
+const Space = optional(whitespace())
+const StringLiteral = regexp(/"([^"]|\\.)*"/g, 'string')
+
+// Utility.
+const match = (s: string) => takeMid(Space, string(s), Space)
+
+// Grammar.
+const Json = grammar({
+  Root(): Parser<Ast.JsonRoot> {
+    return choice(this.Object, this.Array)
+  },
+  Object(): Parser<Ast.JsonObject> {
+    return map(
+      takeMid(
+        match(Terminals.OpenBrace),
+        sepBy(this.ObjectProp, match(Terminals.Comma)),
+        match(Terminals.CloseBrace)
+      ),
+      toObject
+    )
+  },
+  ObjectProp(): Parser<Ast.JsonObjectProp> {
+    return map(sequence(this.String, match(Terminals.Colon), this.Value), toObjectProp)
+  },
+  Array(): Parser<Ast.JsonArray> {
+    return map(
+      takeMid(
+        match(Terminals.OpenSquare),
+        sepBy(this.Value, match(Terminals.Comma)),
+        match(Terminals.CloseSquare)
+      ),
+      toArray
+    )
+  },
+  String(): Parser<Ast.JsonString> {
+    return map(StringLiteral, toString)
+  },
+  Number(): Parser<Ast.JsonNumber> {
+    return map(NumberLiteral, toNumber)
+  },
+  Boolean(): Parser<Ast.JsonBoolean> {
+    return map(choice(match(Keywords.True), match(Keywords.False)), toBoolean)
+  },
+  Null(): Parser<Ast.JsonNull> {
+    return map(match(Keywords.Null), toNull)
+  },
+  Value(): Parser<Ast.JsonValue> {
+    return choice(this.Object, this.Array, this.String, this.Number, this.Boolean, this.Null)
+  }
+})
+
+/* Wrapper for bench runner. */
+
+export function parse(text: string): Ast.JsonRoot {
+  const result = run(Json.Root).with(text)
+
+  switch (result.isOk) {
+    case true: {
+      return result.value
+    }
+
+    case false: {
+      return {
+        type: 'object',
+        values: []
+      }
+    }
+  }
+}
diff --git a/docs/docs/content/core/grammar.md b/docs/docs/content/core/grammar.md
new file mode 100644
index 0000000..7816cf5
--- /dev/null
+++ b/docs/docs/content/core/grammar.md
@@ -0,0 +1,70 @@
+---
+title: 'grammar'
+kind: 'core'
+description: 'This simplifies the creation of a self-contained grammar.'
+---
+
+# grammar
+
+## Description
+
+`grammar` is used to create a self-contained grammar.
+
+Similarly to [defer], this allows for the creation of mutually recursive parsers,
+but lets you define all of the component parsers within a single call.
+
+The function takes an object with parser initializers, and returns an object with
+all of those parsers initialized. Within the parser initializers, use `this` to
+reference other initialized parsers, as in the example below.
+
+The properties of the resulting object are just regular parsers - you can freely
+destructure these, pass them around individually, or compose them with other
+grammars, parsers or combinators as needed.
+
+## Usage
+
+Here is an example of a simple grammar that recursively matches `ab` sequences:
+
+```ts
+const ab = grammar({
+  a(): Parser<string> {
+    return map(
+      sequence(
+        string('a'),
+        optional(this.b)
+      ),
+      ([a, b]) => a + (b ?? '')
+    )
+  },
+  b(): Parser<string> {
+    return map(
+      sequence(
+        string('b'),
+        choice(this.a, this.b)
+      ),
+      ([b, a]) => b + a
+    )
+  }
+})
+```
+
+The individual properties are just regular parsers:
+
+```ts
+const { a } = ab
+
+console.log(run(a).with('abba'))
+```
+
+::: tip Success
+```ts
+{
+  isOk: true,
+  span: [0, 4],
+  pos: 4,
+  value: 'abba'
+}
+```
+:::
+
+[defer]: ../parsers/defer
diff --git a/src/__tests__/core/grammar.spec.ts b/src/__tests__/core/grammar.spec.ts
new file mode 100644
index 0000000..6dc3072
--- /dev/null
+++ b/src/__tests__/core/grammar.spec.ts
@@ -0,0 +1,23 @@
+import { grammar } from '@core'
+import { choice, map, optional, sequence, string } from '@lib'
+import { describe, should, it, run, result } from '@testing'
+
+describe('grammar', () => {
+  it('should create self-contained grammar', () => {
+    const ab = grammar({
+      a() {
+        return map(sequence(string('a'), optional(this.b)), ([a, b]) => a + (b ?? ''))
+      },
+      b() {
+        return map(sequence(string('b'), choice(this.a, this.b)), ([b, a]) => b + a)
+      }
+    })
+
+    const value = 'abba'
+
+    const actual = run(ab.a, value)
+    const expected = result(true, value)
+
+    should.matchState(actual, expected)
+  })
+})
diff --git a/src/core.ts b/src/core.ts
index 2db6579..506bf93 100644
--- a/src/core.ts
+++ b/src/core.ts
@@ -1,2 +1,3 @@
 export * from '@core/run'
 export * from '@core/tryRun'
+export * from '@core/grammar'
diff --git a/src/core/grammar.ts b/src/core/grammar.ts
new file mode 100644
index 0000000..167f335
--- /dev/null
+++ b/src/core/grammar.ts
@@ -0,0 +1,86 @@
+import type { Parser } from '@lib/types'
+
+/**
+ * This type extracts the return-types from the parser initializers.
+ */
+export type Grammar<T> = {
+  [P in keyof T]: T[P] extends () => unknown ? ReturnType<T[P]> : never
+}
+
+/**
+ * This type injects the initialized parser types into `this`, allowing for
+ * type-safe self-contained and mutually recursive grammars.
+ */
+export type GrammarInit<T> = T & ThisType<Grammar<T>>
+
+/**
+ * This defines the input to the `grammar` function - the parser initializers.
+ */
+export type GrammarType = {
+  [name: string]: () => Parser<unknown>
+}
+
+/**
+ * This is a utility function to simplify the creation of a self-contained grammar.
+ *
+ * Similarly to `defer`, this allows for the creation of mutually recursive parsers,
+ * but lets you define all of the component parsers within a single call.
+ *
+ * The function takes an object with parser initializers, and returns an object with
+ * all of those parsers initialized. Within the parser initializers, use `this` to
+ * reference other initialized parsers, as in the example below.
+ *
+ * The properties of the resulting object are just regular parsers - you can freely
+ * destructure these, pass them around individually, or compose them with other
+ * grammars, parsers or combinators as needed.
+ *
+ * @example
+ *
+ * ```typescript
+ * interface NumberNode {
+ *   type: 'number'
+ *   value: number
+ * }
+ *
+ * interface ListNode {
+ *   type: 'list'
+ *   value: Array<NumberNode | ListNode>
+ * }
+ *
+ * const tupleGrammar = grammar({
+ *   tupleNumber(): Parser<NumberNode> {
+ *     return map(integer(), (value, span) => ({ type: 'number', span, value }))
+ *   },
+ *   tupleList(): Parser<ListNode> {
+ *     return map(
+ *       takeMid(
+ *         string('('),
+ *         sepBy(choice(this.tupleList, this.tupleNumber), string(',')),
+ *         string(')')
+ *       ),
+ *       (value, span) => ({ type: 'list', span, value })
+ *     )
+ *   }
+ * })
+ *
+ * const result = run(tupleGrammar.tupleList).with('(1,2,(3,4))')
+ * ```
+ */
+export function grammar<T extends GrammarType>(init: GrammarInit<T>): Grammar<T> {
+  const grammar = {} as { [key: string]: Parser<unknown> }
+
+  for (const key in init) {
+    grammar[key] = {
+      // istanbul ignore next
+      parse() {
+        throw new Error(`internal error`) // this line should never execute
+      }
+    }
+  }
+
+  for (const key in init) {
+    grammar[key].parse = init[key].apply(grammar).parse
+  }
+
+  return grammar as Grammar<T>
+}