Add exit constructor

src/lib/painter/lifecycle.ts

@@ -16,21 +16,26 @@ import {
   origin,
 } from './canvas'
 
-interface PainterExit extends Tag<'PainterExit'> {}
+interface PainterExit<E> extends Tag<'PainterExit'> {
+  value: Either<E, Error>
+}
 
-interface PainterTask<T extends object = {}> extends Tag<'PainterTask'> {
+interface PainterTask<E, T extends object = {}> extends Tag<'PainterTask'> {
   task: {
     origin: CanvasOrigin,
     end: CanvasEnd,
-    effect: PainterEffect<T & Tag<'PainterState'>>,
+    effect: PainterEffect<E, T>,
     state: Option<T & Tag<'PainterState'>>,
   }
 }
 
-type TaskConstructor<T extends object = {}> = (
+type TaskConstructor = (
   x: CursorPos,
   y: CursorPos,
-) => (f: PainterEffect, state?: T & Tag<'PainterState'>) => PainterTask<T>
+) => <E = number, T extends object = {}>(
+  f: PainterEffect<E, T>,
+  state?: T & Tag<'PainterState'>,
+) => PainterTask<E, T>
 const task: TaskConstructor = (x, y) => (f, state?) => {
   return {
     _tag: 'PainterTask',
@@ -43,14 +48,25 @@ const task: TaskConstructor = (x, y) => (f, state?) => {
   }
 }
 
+type ExitConstructor = <T>(x: Either<T, Error>) => PainterExit<T>
+const exit: ExitConstructor = x => ({_tag: 'PainterExit', value: x})
+
 type PainterEffect<
+  E,
   T extends object = {},
-> = (task: PainterTask<T>) => Either<PainterTask<T>, PainterExit>
+> = (task: PainterTask<T>) => Either<PainterTask<T>, PainterExit<E>>
 
 type EffectState = <T extends object = {}>(x: T) => T & Tag<'PainterState'>
 const effectState: EffectState = x => ({_tag: 'PainterState', ...x})
 
-export { type PainterEffect, task }
+export {
+  type EffectState as PainterState,
+  effectState as tagState,
+  exit,
+  type PainterEffect,
+  type PainterTask,
+  task,
+}
 
 //
 // testing