diff --git a/jsconfig.json b/jsconfig.json
index 4f05d0e..c30033e 100644
--- a/jsconfig.json
+++ b/jsconfig.json
@@ -1,12 +1,9 @@
 {
   "compilerOptions": {
-    "module": "es2020",
+    "module": "node",
     "target": "es6",
     "lib": ["esnext", "dom"],
     "checkJs": true,
-    "paths": {
-      "/*": ["./*"]
-    }
   },
   "exclude": [
     "node_modules"
diff --git a/src/function.js b/src/function.js
index c2e335c..566400d 100644
--- a/src/function.js
+++ b/src/function.js
@@ -1,6 +1,6 @@
 import { curry, curryN } from './curry.js'
 import { dispatch } from './fantasy-land.js'
-import { head, isIterable, iterConcat, iter, tail } from './list.js'
+import { head, isIterable, concatIter, iter, tail } from './list.js'
 
 /** @import { Fn, Morphism, InferredMorphism, Predicate } from './types.js' */
 
@@ -13,10 +13,12 @@ export const id = x => x
 
 export const concat = dispatch(['fantasy-land/concat', 'concat'],
   (b, a) => {
-    if (isIterable(a) || isIterable(b)) {
-      return iterConcat(iter(a), iter(b))
-    } else {
+    if (Array.isArray(a) && (Array.isArray(b) || !isIterable(b))) {
       return a.concat(b)
+    } else if (Array.isArray(b) && (Array.isArray(a) || !isIterable(a))) {
+      return b.concat(a)
+    } else {
+      return concatIter(iter(a), iter(b))
     }
   })
 
@@ -122,7 +124,7 @@ export const ap = dispatch(['fantasy-land/ap', 'ap'],
     const args = liftA(a)
 
     const xs = fs.reduce((acc, f) => (
-      concat(acc, iter(map(f, args)))
+      concat(acc, map(f, args))
     ), [])
 
     return [...xs]
diff --git a/src/list.js b/src/list.js
index b0cf35a..ac9f65b 100644
--- a/src/list.js
+++ b/src/list.js
@@ -29,7 +29,7 @@ export function* iter(value) {
  * @param {...(Iterable<T> | Iterator<T>)} iterators
  * @yields {T}
  */
-export const iterConcat = function*(...iterators) {
+export const concatIter = function*(...iterators) {
   for (const iter of iterators) {
     for (const item of Iterator.from(iter)) {
       yield item
diff --git a/test/units/dispatch.js b/test/units/dispatch.js
new file mode 100644
index 0000000..6ec5bd5
--- /dev/null
+++ b/test/units/dispatch.js
@@ -0,0 +1,62 @@
+import { it, assert, assertEq } from 'folktest'
+import { dispatch } from '../../src/fantasy-land.js'
+
+const test = (re, str = '') => re instanceof RegExp ? re.test(str) : new RegExp(re).test(str)
+
+const assertErr = (f, err) => {
+  try {
+    f()
+  } catch (e) {
+    if (typeof err === 'string' || err instanceof RegExp) {
+      assert(test(err, e.message), `${err} did not match ${e.message}`)
+    } else if (typeof err === 'function') {
+      assert(e.constructor === err)
+    }
+
+    return
+  }
+
+  const expected = err ? `"${err}" ` : ""
+  assert(false, `expecting error ${expected}but function did not throw`)
+}
+
+const wrong = msg => assert(false, msg)
+
+export const Dispatch = [
+  it('should dispatch to any listed method or fallback', () => {
+    const a1 = {
+      ['fantasy-land/test']: x => assertEq(x, 1),
+      test: () => wrong(`a1['test'] should not have been called`)
+    }
+
+    const f1 = dispatch(['fantasy-land/test', 'test'], (v, x) => {
+      wrong(`f1 fallback should not have been called for ${JSON.stringify(x)}`)
+    })
+
+    f1(1, a1)
+
+    delete a1['fantasy-land/test']
+
+    assertErr(() => {
+      f1(1, a1)
+    })
+
+    const f2 = dispatch(['test', 'fantasy-land/test'], (v, x) => {
+      wrong(`f2 fallback should not have been called for ${JSON.stringify(x)}`)
+    })
+
+    const a2 = {
+      ['fantasy-land/test']: () => wrong(`a2['fantasy-land/test'] should not have been called`),
+      test: x => assertEq(x, 2)
+    }
+
+    f2(2, a2)
+
+    const f3 = dispatch(['fantasy-land/test', 'test'], x => {
+      assertEq(x, 3)
+    })
+
+    f3(3, {})
+  })
+]
+
diff --git a/test/units/function.js b/test/units/function.js
new file mode 100644
index 0000000..4ef6512
--- /dev/null
+++ b/test/units/function.js
@@ -0,0 +1,19 @@
+import { it, assert, assertEq } from 'folktest'
+import { concat } from '../..//src/function.js'
+import { isIterable, iter } from '../..//src/list.js'
+
+export const Functions = [
+  it('concat', () => {
+    assertEq(concat(1, []), [1])
+    assertEq(concat([], 1), [1])
+    assertEq(concat([2], [1]), [1, 2])
+    const a = concat([2], iter([1]))
+    assert(isIterable(a), 'concat([2], iter([1])) returned a non-iterable')
+    assertEq([...a], [1, 2])
+
+    const b = concat(iter([2]), [1])
+    assert(isIterable(b), 'concat(iter([2]), [1]) returned a non-iterable')
+    assertEq([...b], [1, 2])
+  })
+]
+
diff --git a/test/units/index.js b/test/units/index.js
index 6ec5bd5..d7dd892 100644
--- a/test/units/index.js
+++ b/test/units/index.js
@@ -1,62 +1,3 @@
-import { it, assert, assertEq } from 'folktest'
-import { dispatch } from '../../src/fantasy-land.js'
-
-const test = (re, str = '') => re instanceof RegExp ? re.test(str) : new RegExp(re).test(str)
-
-const assertErr = (f, err) => {
-  try {
-    f()
-  } catch (e) {
-    if (typeof err === 'string' || err instanceof RegExp) {
-      assert(test(err, e.message), `${err} did not match ${e.message}`)
-    } else if (typeof err === 'function') {
-      assert(e.constructor === err)
-    }
-
-    return
-  }
-
-  const expected = err ? `"${err}" ` : ""
-  assert(false, `expecting error ${expected}but function did not throw`)
-}
-
-const wrong = msg => assert(false, msg)
-
-export const Dispatch = [
-  it('should dispatch to any listed method or fallback', () => {
-    const a1 = {
-      ['fantasy-land/test']: x => assertEq(x, 1),
-      test: () => wrong(`a1['test'] should not have been called`)
-    }
-
-    const f1 = dispatch(['fantasy-land/test', 'test'], (v, x) => {
-      wrong(`f1 fallback should not have been called for ${JSON.stringify(x)}`)
-    })
-
-    f1(1, a1)
-
-    delete a1['fantasy-land/test']
-
-    assertErr(() => {
-      f1(1, a1)
-    })
-
-    const f2 = dispatch(['test', 'fantasy-land/test'], (v, x) => {
-      wrong(`f2 fallback should not have been called for ${JSON.stringify(x)}`)
-    })
-
-    const a2 = {
-      ['fantasy-land/test']: () => wrong(`a2['fantasy-land/test'] should not have been called`),
-      test: x => assertEq(x, 2)
-    }
-
-    f2(2, a2)
-
-    const f3 = dispatch(['fantasy-land/test', 'test'], x => {
-      assertEq(x, 3)
-    })
-
-    f3(3, {})
-  })
-]
+export * from './dispatch.js'
+export * from './function.js'