feat(join): Support join()

index.js

@@ -1,6 +1,7 @@
 exports.hash = require('./hash')
 exports.oneOf = require('./oneOf')
 exports.tuple = require('./tuple')
+exports.join = require('./join')
 
 exports.int = require('./int')
 exports.float = require('./float')

index.mjs

@@ -1,6 +1,7 @@
 export { default as hash } from './has'
 export { default as oneOf } from './oneOf'
 export { default as tuple } from './tuple'
+export { default as join } from './join'
 
 export { default as int } from './int'
 export { default as float } from './float'

join.js

@@ -0,0 +1,19 @@
+var tuple = require('./tuple')
+
+function join(a, b, c) {
+  return a != null && b != null && c == null
+    ? joinCurried(a, b)
+    : joinMain(a, b, c)
+}
+
+function joinMain(id, joinerFn, makerFns) {
+  return joinerFn(tuple(id, makerFns))
+}
+
+function joinCurried(joinerFn, makerFns) {
+  return function joinFn(id) {
+    return joinMain(id, joinerFn, makerFns)
+  }
+}
+
+module.exports = join