From 706bfc7eb2f07d810e00130be003ba7bfc81f2b7 Mon Sep 17 00:00:00 2001
From: Sean May <sean.j.may@gmail.com>
Date: Mon, 16 Jul 2018 01:13:53 -0400
Subject: [PATCH] No, really, though...

---
 src/guards/guards.ts       | 11 +++++++++++
 src/operators/operators.ts | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 src/guards/guards.ts
 create mode 100644 src/operators/operators.ts

diff --git a/src/guards/guards.ts b/src/guards/guards.ts
new file mode 100644
index 0000000..8439862
--- /dev/null
+++ b/src/guards/guards.ts
@@ -0,0 +1,11 @@
+import { ValueTypeGuard } from "../types";
+
+const isTypeof = <T>(type: T): ValueTypeGuard<T> => (x: T): x is T => typeof x === typeof type;
+
+const isString = isTypeof(String());
+const isNumber = isTypeof(Number());
+const isBoolean = isTypeof(Boolean());
+
+const isArray = <T>(xs: T[]): xs is T[] => Array.isArray(xs);
+
+export { isString, isNumber, isBoolean, isArray, isTypeof };
\ No newline at end of file
diff --git a/src/operators/operators.ts b/src/operators/operators.ts
new file mode 100644
index 0000000..5f893e5
--- /dev/null
+++ b/src/operators/operators.ts
@@ -0,0 +1,32 @@
+import { TypedTest, Erratic } from "../types";
+
+const isNull = <T>(x: Erratic<T>): x is null => x === null;
+const isUndefined = <T>(x: Erratic<T>): x is undefined => x === undefined;
+
+const isErratic = <T>(x: Erratic<T>): x is null | undefined =>
+  isNull(x) || isUndefined(x);
+
+const and = <T>(...tests: TypedTest<T>[]) => (x: Erratic<T>): x is T =>
+  isErratic(x) ? false : tests.every(test => test(x));
+
+const or = <T>(...tests: TypedTest<T>[]) => (x: Erratic<T>): x is T =>
+  isErratic(x) ? false : tests.some(test => test(x));
+
+const optional = <T>(test: TypedTest<T>) => (x: Erratic<T>): x is T =>
+  isNull(x) ? false : isUndefined(x) ? true : test(x);
+
+const nullable = <T>(test: TypedTest<T>) => (x: Erratic<T>): x is T =>
+  isNull(x) ? true : isUndefined(x) ? false : test(x);
+
+const erratic = <T>(test: TypedTest<T>) => (x: Erratic<T>): x is T =>
+  isErratic(x) ? true : test(x);
+
+const compose = and;
+
+const customTest = <T>(test: TypedTest<T>) => (x: Erratic<T>): x is T =>
+  isErratic(x) ? false : test(x);
+
+const unsafeTest = <T>(test: TypedTest<Erratic<T>>) => (x: Erratic<T>): x is T =>
+  test(x);
+
+export { compose, and, or, optional, nullable, erratic, customTest, unsafeTest };