Add the matches pattern helper

README.mz

@@ -24,7 +24,9 @@ npm install patroon
 ```js node -
 const {
 
+  // Match Helpers
   patroon,
+  matches,
 
   // Pattern Helpers
   every,
@@ -392,6 +394,31 @@ patroon(
 )([{a: 43}])
 ```
 
+### Matches
+
+A pattern matching helper that can help with using patroon patterns in if
+statements and such.
+
+```js ./tape-test
+const isUser = matches({user: _})
+const isAdmin = matches({user: {admin: true}})
+
+const user = {
+  user: {
+    id: 2
+  }
+}
+
+const admin = {
+  user: {
+    id: 1,
+    admin: true
+  }
+}
+
+JSON.stringify([isUser(admin), isUser(user), isAdmin(admin), isAdmin(user)])
+```
+
 ### Custom Helper
 
 It is very easy to write your own helpers. All the builtin helpers are really

src/index.js

@@ -108,6 +108,13 @@ function instanceOf (ctor) {
   return value => value instanceof ctor
 }
 
+function matches (pattern) {
+  return patroon(
+    pattern, true,
+    T, false
+  )
+}
+
 module.exports = Object.assign(patroon, {
   NoMatchError,
   UnevenArgumentCountError,
@@ -121,5 +128,6 @@ module.exports = Object.assign(patroon, {
   typed,
   t: typed,
   instanceOf,
+  matches,
   _: T
 })

src/index.test.js

@@ -5,6 +5,7 @@ const { version } = require('../package')
 const {
   reference,
   instanceOf,
+  matches,
   typed,
   t,
   ref,
@@ -227,6 +228,26 @@ test('Does not match on reference', t => {
   t.end()
 })
 
+test('Matches function', check(gen.any, gen.any, (t, a, b) => {
+  t.ok(matches(a)(a))
+  t.equals(typeof matches(a)(b), 'boolean')
+  t.end()
+}))
+
+test('Check that matches throws non patroon errors', t => {
+  class SomeError extends Error { }
+
+  const predicate = () => {
+    throw new SomeError()
+  }
+  const pattern = {
+    predicate
+  }
+
+  t.throws(() => matches(pattern)({ predicate: 2 }), SomeError)
+  t.end()
+})
+
 if (version.startsWith('2')) {
   test('Deprecated functions in version 2', t => {
     t.plan(3)

tape-test

@@ -4,6 +4,7 @@ cat <(echo '
 const {
   _,
   every,
+  matches,
   instanceOf,
   some,
   multi,