Added condOf

README.md

@@ -61,6 +61,7 @@ parts.  [Try Lenses!](https://calmm-js.github.io/partial.lenses/playground.html)
       * [`L.choices(optic, ...optics) ~> optic`](#L-choices "L.choices: (POptic s a, ...POptic s a) -> POptic s a") <small><sup>v11.10.0</sup></small>
       * [`L.choose((maybeValue, index) => optic) ~> optic`](#L-choose "L.choose: ((Maybe s, Index) -> POptic s a) -> POptic s a") <small><sup>v1.0.0</sup></small>
       * [`L.cond(...[(maybeValue, index) => testable, consequentOptic][, [alternativeOptic]]) ~> optic`](#L-cond "L.cond: (...[(Maybe s, Index) -> Boolean, PLens s a][, [PLens s a]]) -> PLens s a") <small><sup>v13.1.0</sup></small>
+      * [`L.condOf(lens, ...[(maybeValue, index) => testable, consequentOptic][, [alternativeOptic]]) ~> optic`](#L-condOf "L.condOf: (PLens s c, ...[(Maybe c, Index) -> Boolean, PLens s a][, [PLens s a]]) -> PLens s a") <small><sup>v13.5.0</sup></small>
       * [`L.ifElse((maybeValue, index) => testable, optic, optic) ~> optic`](#L-ifElse "L.ifElse: ((Maybe s, Index) -> Boolean) -> POptic s a -> POptic s a -> POptic s a") <small><sup>v13.1.0</sup></small>
       * ~~[`L.iftes((maybeValue, index) => testable, consequentOptic, ...[, alternativeOptic]) ~> optic`](#L-iftes "L.iftes: ((Maybe s, Index) -> Boolean) -> PLens s a -> PLens s a -> PLens s a") <small><sup>v11.14.0</sup></small>~~
       * [`L.orElse(backupOptic, primaryOptic) ~> optic`](#L-orElse "L.orElse: (POptic s a, POptic s a) -> POptic s a") <small><sup>v2.1.0</sup></small>
@@ -1255,8 +1256,8 @@ L.modify(majorAxis, R.negate, {x: -3, y: 1})
 ##### <a id="L-cond"></a> [≡](#contents) [▶](https://calmm-js.github.io/partial.lenses/index.html#L-cond) [`L.cond(...[(maybeValue, index) => testable, consequentOptic][, [alternativeOptic]]) ~> optic`](#L-cond "L.cond: (...[(Maybe s, Index) -> Boolean, PLens s a][, [PLens s a]]) -> PLens s a") <small><sup>v13.1.0</sup></small>
 
 `L.cond` creates an optic whose operation is selected from the given optics and
-predicates on the underlying view.  See also [`L.choose`](#L-choose) and
-[`L.ifElse`](#L-ifElse).
+predicates on the underlying view.  See also [`L.condOf`](#L-condOf),
+[`L.choose`](#L-choose) and [`L.ifElse`](#L-ifElse).
 
 ```jsx
 L.cond( [ predicate, consequent ]
@@ -1307,6 +1308,25 @@ vice versa.  [`L.choose`](#L-choose) not only allows the optic to be chosen
 dynamically, but also allows the optic to be constructed dynamically and using
 the data at the focus.
 
+##### <a id="L-condOf"></a> [≡](#contents) [▶](https://calmm-js.github.io/partial.lenses/index.html#L-condOf) [`L.condOf(lens, ...[(maybeValue, index) => testable, consequentOptic][, [alternativeOptic]]) ~> optic`](#L-condOf "L.condOf: (PLens s c, ...[(Maybe c, Index) -> Boolean, PLens s a][, [PLens s a]]) -> PLens s a") <small><sup>v13.5.0</sup></small>
+
+`L.condOf` is like [`L.cond`](#L-cond) except the first argument to `L.condOf`
+is a lens to get the parameters for the predicates from the underlying view.
+
+For example:
+
+```js
+L.get(
+  L.condOf(
+    'type',
+    [R.equals('title'), 'text'],
+    [R.equals('text'), 'body']
+  ),
+  {type: 'text', body: 'Try writing this with `L.cond`.'}
+)
+// 'Try writing this with `L.cond`.'
+```
+
 ##### <a id="L-ifElse"></a> [≡](#contents) [▶](https://calmm-js.github.io/partial.lenses/index.html#L-ifElse) [`L.ifElse((maybeValue, index) => testable, optic, optic) ~> optic`](#L-ifElse "L.ifElse: ((Maybe s, Index) -> Boolean) -> POptic s a -> POptic s a -> POptic s a") <small><sup>v13.1.0</sup></small>
 
 `L.ifElse` creates an optic whose operation is selected based on the given

src/partial.lenses.js

@@ -727,6 +727,10 @@ const seq2U = (l, r) => (x, i, M, xi2yM) =>
 
 const pickInAux = (t, k) => [k, pickIn(t)]
 
+//
+
+const condOfCase = (p, o, r) => (y, j) => (p(y, j) ? o : r(y, j))
+
 // Auxiliary
 
 export const seemsArrayLike = x =>
@@ -812,6 +816,27 @@ export const cond = (process.env.NODE_ENV === 'production'
   return r
 })
 
+export const condOf = (process.env.NODE_ENV === 'production'
+  ? I.id
+  : fn => (of, ...cs) => {
+      const pair = C.tup(C.ef(reqFn), C.ef(reqOptic))
+      C.arr(pair)(cs.slice(0, -1))
+      C.arr(C.or(C.tup(C.ef(reqOptic)), pair))(cs.slice(-1))
+      return fn(of, ...cs)
+    })(function(of) {
+  of = toFunction(of)
+  let op = undefined
+  let n = arguments.length
+  while (--n) {
+    const c = arguments[n]
+    op =
+      c.length === 1
+        ? I.always(toFunction(c[0]))
+        : condOfCase(c[0], toFunction(c[1]), op || I.always(zero))
+  }
+  return (x, i, C, xi2yC) => of(x, i, Const, op)(x, i, C, xi2yC)
+})
+
 export const ifElse = I.curry((c, t, e) =>
   ifteU(c, toFunction(t), toFunction(e))
 )

test/tests.js

@@ -218,6 +218,7 @@ describe('arities', () => {
     concat: 3,
     concatAs: 4,
     cond: 0,
+    condOf: 1,
     count: 2,
     countIf: 3,
     counts: 2,
@@ -1422,6 +1423,46 @@ describe('L.cond', () => {
   )
 })
 
+describe('L.condOf', () => {
+  testEq(
+    `L.collect(
+       [
+         L.elems,
+         L.condOf(
+           'type',
+           [R.equals('a'), 'foo'],
+           [R.equals('b'), 'bar'],
+           ['lol']
+         )
+       ],
+       [
+         {type: 'a', foo: 42},
+         {type: 'b', bar: 101},
+         {type: 'c', lol: 76}
+       ]
+     )`,
+    [42, 101, 76]
+  )
+  testEq(
+    `L.collect(
+       [
+         L.elems,
+         L.condOf(
+           'type',
+           [R.equals('a'), 'foo'],
+           [R.equals('b'), 'bar']
+         )
+       ],
+       [
+         {type: 'a', foo: 42},
+         {type: 'b', bar: 101},
+         {type: 'c', lol: 76}
+       ]
+     )`,
+    [42, 101]
+  )
+})
+
 describe('L.ifElse', () => {
   testEq(`L.set(L.ifElse(R.not, L.setOp(1), L.zero), 3, 2)`, 2)
   testEq(`L.set(L.ifElse(R.not, L.setOp(1), L.zero), 3, 0)`, 1)

test/types.js

@@ -103,6 +103,7 @@ export const lazy = T.fn([T.fn([T_optic], T_optic)], T_optic)
 export const choices = T.fnVarN(1, T_optic, T_optic)
 export const choose = T.fn([T.fn([T_maybeDataO, T_index], T_optic)], T_optic)
 export const cond = T.fnVarN(0, T.any, T_optic)
+export const condOf = T.fnVarN(1, T.any, T_optic)
 export const ifElse = T.fn(
   [T.fn([T_maybeDataO, T_index], T.any), T_optic, T_optic],
   T_optic