feat: Add "not" for negating a predicate

Author: andreidmt

src/index.js

@@ -33,7 +33,7 @@ export { i } from "./i/i"
 export { inc } from "./inc/inc"
 export { indexBy } from "./index-by/index-by"
 export { intersect } from "./intersect/intersect"
-export { is, isNothing, isTrue, isFalse, isObject } from "./is/is"
+export { is, isNothing, not, isTrue, isFalse, isObject } from "./is/is"
 export { isEmpty, isNotEmpty } from "./is-empty/is-empty"
 export { isMatch } from "./is-match/is-match"
 export { join } from "./join/join"

src/is/is.js

@@ -30,4 +30,6 @@ const isTrue = source => source === true
 
 const isFalse = source => source === false
 
-export { is, isNothing, isTrue, isFalse, isObject }
+const not = fn => source => !fn(source)
+
+export { is, not, isNothing, isTrue, isFalse, isObject }

src/is/is.test.js

@@ -1,5 +1,5 @@
 import test from "tape"
-import { is, isNothing, isTrue, isFalse, isObject } from ".."
+import { is, isNothing, isTrue, not, isFalse, isObject } from ".."
 
 /**
  * Test if something is not `null` or `undefined`
@@ -28,6 +28,8 @@ test("core::is", t => {
   t.equal(is(undefined), false, 'Is "undefined" something')
   t.equal(is(NaN), false, 'Is "NaN" something')
 
+  t.equal(not(is)(NaN), true, '"NaN" is not something')
+
   t.equal(isTrue(""), false, "empty string is not true")
   t.equal(isTrue(true), true, "boolean value true is true")