diff --git a/src/vm.ts b/src/vm.ts
index 9294a35..e0b122e 100644
--- a/src/vm.ts
+++ b/src/vm.ts
@@ -11,22 +11,25 @@ import {
  */
 export type ScriptType = "action" | "render";
 
-export type Proc = (state: Vm, argv: TextPiece[]) => TextPiece;
+export type Proc<Context> = (
+  state: Vm<Context>,
+  argv: TextPiece[]
+) => TextPiece;
 
 /**
  * State for running a script in.
  */
-export type Vm = {
+export type Vm<Context = {}> = {
   /** Mutability status */
   mode: ScriptType;
   /** Implementations of commands scripts can run */
-  commands: Record<string, Proc>;
+  commands: Record<string, Proc<Context>>;
   /** Markup to render / output */
   output: string;
-};
+} & Context;
 
-function evaluateWord(
-  state: Vm,
+function evaluateWord<Context>(
+  state: Vm<Context>,
   word: Word | InterpolatedPiece
 ): TextWord | BareWord | HtmlWord {
   if ("bare" in word || "text" in word || "html" in word) {
@@ -50,8 +53,8 @@ function evaluateWord(
  * @param onReturn callback optionally invoked with the return word for each top-level command (not triggered by command substitutions)
  * @returns the return word of the final command in the script, or empty text if the script is empty.
  */
-export function runNoctl(
-  state: Vm,
+export function runNoctl<Context>(
+  state: Vm<Context>,
   script: Script,
   onReturn?: (word: TextPiece) => void
 ): TextPiece {