better filter typings

dtslint/ts4.7/index.ts

@@ -15,23 +15,37 @@ type ST = readonly [string, number]
 type TT = readonly [boolean, number]
 
 //
-// key
+// at
 //
 
 // $ExpectType Lens<S, string>
-Optic.id<S>().compose(Optic.key('a'))
+Optic.id<S>().compose(Optic.at('a'))
 
 // $ExpectType PolyLens<S, T, string, boolean>
-Optic.id<S, T>().compose(Optic.key<S, 'a', boolean>('a'))
+Optic.id<S, T>().compose(Optic.at<S, 'a', boolean>('a'))
 
 // $ExpectType Lens<ST, string>
-Optic.id<ST>().compose(Optic.key('0'))
+Optic.id<ST>().compose(Optic.at('0'))
 
 // $ExpectType PolyLens<ST, TT, string, boolean>
-Optic.id<ST, TT>().compose(Optic.key<ST, '0', boolean>('0'))
+Optic.id<ST, TT>().compose(Optic.at<ST, '0', boolean>('0'))
 
 // $ExpectType PolyLens<S, { readonly a: boolean; readonly b: number; }, string, boolean>
-Optic.key<S, 'a', boolean>('a')
+Optic.at<S, 'a', boolean>('a')
 
 // $ExpectType PolyLens<ST, readonly [boolean, number], string, boolean>
-Optic.key<ST, '0', boolean>('0')
+Optic.at<ST, '0', boolean>('0')
+
+//
+// filter
+//
+
+declare const isString: (u: unknown) => u is string
+
+// $ExpectType Prism<string | number, string>
+Optic.id<string | number>().compose(Optic.filter(isString))
+
+declare const predicate: (u: string | number | boolean) => boolean
+
+// $ExpectType Prism<string | number, string | number>
+Optic.id<string | number>().compose(Optic.filter(predicate))

src/index.ts

@@ -404,7 +404,7 @@ export const cons: {
  */
 export const nonNullable = <S>(): Prism<S, NonNullable<S>> =>
   prism(
-    (s) => s == null ? E.left(new Error(`${s} did not satisfy isNonNullable`)) : E.right(s),
+    (s) => s == null ? E.left(new Error(`${s} did not satisfy isNonNullable`)) : E.right(s as any),
     identity
   )
 
@@ -414,8 +414,8 @@ export const nonNullable = <S>(): Prism<S, NonNullable<S>> =>
  * @since 1.0.0
  */
 export const filter: {
-  <S, A extends S>(refinement: Refinement<S, A>): Prism<S, A>
-  <S>(predicate: Predicate<S>): Prism<S, S>
+  <S extends A, B extends A, A = S>(refinement: Refinement<A, B>): Prism<S, B>
+  <S extends A, A = S>(predicate: Predicate<A>): Prism<S, S>
 } = <S>(predicate: Predicate<S>): Prism<S, S> =>
   prism(
     (s) =>