Transform for F#-style await

Inludes support for optimizing single-parameter arrow functions

packages/babel-plugin-proposal-pipeline-operator/src/fsharpVisitor.js

@@ -0,0 +1,55 @@
+import { types as t } from "@babel/core";
+
+const fsharpVisitor = {
+  BinaryExpression(path) {
+    const { scope } = path;
+    const { node } = path;
+    const { operator, left } = node;
+    let { right } = node;
+    if (operator !== "|>") return;
+
+    let optimizeArrow =
+      t.isArrowFunctionExpression(right) &&
+      t.isExpression(right.body) &&
+      !right.async &&
+      !right.generator;
+    let param;
+
+    if (optimizeArrow) {
+      const { params } = right;
+      if (params.length === 1 && t.isIdentifier(params[0])) {
+        param = params[0];
+      } else if (params.length > 0) {
+        optimizeArrow = false;
+      }
+    } else if (t.isIdentifier(right, { name: "eval" })) {
+      right = t.sequenceExpression([t.numericLiteral(0), right]);
+    }
+
+    if (optimizeArrow && !param) {
+      // Arrow function with 0 arguments
+      path.replaceWith(t.sequenceExpression([left, right.body]));
+      return;
+    }
+
+    const placeholder = scope.generateUidIdentifierBasedOnNode(param || left);
+    scope.push({ id: placeholder });
+    if (param) {
+      path.get("right").scope.rename(param.name, placeholder.name);
+    }
+
+    const applied =
+      right.type === "AwaitExpression"
+        ? t.awaitExpression(t.cloneNode(placeholder))
+        : t.callExpression(right, [t.cloneNode(placeholder)]);
+    const call = optimizeArrow ? right.body : applied;
+    path.replaceWith(
+      t.sequenceExpression([
+        t.assignmentExpression("=", t.cloneNode(placeholder), left),
+        call,
+      ]),
+    );
+  },
+};
+
+export default fsharpVisitor;

packages/babel-plugin-proposal-pipeline-operator/src/index.js

@@ -2,10 +2,12 @@ import { declare } from "@babel/helper-plugin-utils";
 import syntaxPipelineOperator from "@babel/plugin-syntax-pipeline-operator";
 import minimalVisitor from "./minimalVisitor";
 import smartVisitor from "./smartVisitor";
+import fsharpVisitor from "./fsharpVisitor";
 
 const visitorsPerProposal = {
   minimal: minimalVisitor,
   smart: smartVisitor,
+  fsharp: fsharpVisitor,
 };
 
 export default declare((api, options) => {

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/arrow-functions-parenless/exec.js

@@ -0,0 +1,34 @@
+const y = 2;
+
+const f = (x) => (x
+  |> (y) => y + 1)
+  |> (z) => z * y
+
+const _f = (x) => x
+  |> (y) => y + 1
+  |> (z) => z * y
+
+const g = (x) => x
+  |> (y) => (
+    y + 1
+    |> (z) => z * y
+  )
+
+const _g = (x) => x
+  |> (y => (
+    y + 1
+    |> (z) => z * y)
+  )
+
+const __g = (x) => x
+  |> (y => { return (
+    y + 1
+    |> (z) => z * y);
+    }
+  )
+
+expect(  f(1)).toBe(4);
+expect( _f(1)).toBe(4);
+expect(  g(1)).toBe(2);
+expect( _g(1)).toBe(2);
+expect(__g(1)).toBe(2);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/arrow-functions/exec.js

@@ -0,0 +1,14 @@
+var result = [5,10]
+  |> (_ => _.map(x => x * 2))
+  |> (_ => _.reduce( (a,b) => a + b ))
+  |> (sum => sum + 1)
+
+expect(result).toBe(31);
+
+
+var inc = (x) => x + 1;
+var double = (x) => x * 2;
+
+var result2 = [4, 9].map( x => x |> inc |> double )
+
+expect(result2).toEqual([10, 20]);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/arrow-functions/input.js

@@ -0,0 +1,14 @@
+var result = [5,10]
+  |> (_ => _.map(x => x * 2))
+  |> (_ => _.reduce( (a,b) => a + b ))
+  |> (sum => sum + 1)
+
+expect(result).toBe(31);
+
+
+var inc = (x) => x + 1;
+var double = (x) => x * 2;
+
+var result2 = [4, 9].map( x => x |> inc |> double )
+
+expect(result2).toEqual([10, 20]);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/arrow-functions/output.js

@@ -0,0 +1,15 @@
+var _sum, _ref, _ref2;
+
+var result = (_sum = (_ref = (_ref2 = [5, 10], _ref2.map(x => x * 2)), _ref.reduce((a, b) => a + b)), _sum + 1);
+expect(result).toBe(31);
+
+var inc = x => x + 1;
+
+var double = x => x * 2;
+
+var result2 = [4, 9].map(x => {
+  var _ref3, _x;
+
+  return _ref3 = (_x = x, inc(_x)), double(_ref3);
+});
+expect(result2).toEqual([10, 20]);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/await/exec.js

@@ -0,0 +1,13 @@
+const triple = (x) => x * 3;
+
+async function myFunction(n) {
+  return n
+    |> Math.abs
+    |> Promise.resolve
+    |> await
+    |> triple;
+}
+
+return myFunction(-7).then(result => {
+  expect(result).toBe(21);
+});

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/await/input.js

@@ -0,0 +1,6 @@
+async function myFunction(n) {
+  return n
+    |> Math.abs
+    |> Promise.resolve
+    |> await;
+}

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/await/options.json

@@ -0,0 +1,9 @@
+{
+  "plugins": [
+    ["proposal-pipeline-operator", { "proposal": "fsharp" }]
+  ],
+  "parserOpts": {
+    "allowReturnOutsideFunction": true
+  },
+  "minNodeVersion": "8.0.0"
+}

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/await/output.js

@@ -0,0 +1,5 @@
+async function myFunction(n) {
+  var _ref, _ref2, _n;
+
+  return _ref = (_ref2 = (_n = n, Math.abs(_n)), Promise.resolve(_ref2)), await _ref;
+}

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/basic/exec.js

@@ -0,0 +1,3 @@
+var inc = (x) => x + 1
+
+expect(10 |> inc).toBe(11);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/basic/input.js

@@ -0,0 +1,3 @@
+var inc = (x) => x + 1
+
+expect(10 |> inc).toBe(11);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/basic/output.js

@@ -0,0 +1,5 @@
+var _;
+
+var inc = x => x + 1;
+
+expect((_ = 10, inc(_))).toBe(11);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/indirect-eval/exec.js

@@ -0,0 +1,7 @@
+(function() {
+  'use strict';
+  var result = '(function() { return this; })()'
+    |> eval;
+
+  expect(result).not.toBeUndefined();
+})();

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/indirect-eval/input.js

@@ -0,0 +1,7 @@
+(function() {
+  'use strict';
+  var result = '(function() { return this; })()'
+    |> eval;
+
+  expect(result).not.toBeUndefined();
+})();

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/indirect-eval/output.js

@@ -0,0 +1,8 @@
+(function () {
+  'use strict';
+
+  var _functionReturn;
+
+  var result = (_functionReturn = '(function() { return this; })()', (0, eval)(_functionReturn));
+  expect(result).not.toBeUndefined();
+})();

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/optimize-0-param-arrow/exec.js

@@ -0,0 +1,8 @@
+var a = 1,
+    b = 2,
+    c = 3;
+var result = a
+  |> (() => b)
+  |> (() => c);
+
+expect(result).toBe(c);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/optimize-0-param-arrow/input.js

@@ -0,0 +1,8 @@
+var a = 1,
+    b = 2,
+    c = 3;
+var result = a
+  |> (() => b)
+  |> (() => c);
+
+expect(result).toBe(c);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/optimize-0-param-arrow/output.js

@@ -0,0 +1,5 @@
+var a = 1,
+    b = 2,
+    c = 3;
+var result = ((a, b), c);
+expect(result).toBe(c);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/options.json

@@ -0,0 +1,8 @@
+{
+  "plugins": [
+    ["proposal-pipeline-operator", { "proposal": "fsharp" }]
+  ],
+  "parserOpts": {
+    "allowReturnOutsideFunction": true
+  }
+}

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/minimal/arrow-functions-parenless/exec.js

@@ -0,0 +1,20 @@
+const y = 2;
+const f = (x) => x
+  |> (y => y + 1)
+  |> (z => z * y)
+
+const g = (x) => x
+  |> (y =>
+    y + 1
+    |> (z => z * y)
+  )
+
+const h = (x) => x
+  |> (y => (
+    y + 1
+    |> (z => z * y)
+  ))
+
+expect(f(1)).toBe(4);
+expect(g(1)).toBe(2);
+expect(h(1)).toBe(2);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/minimal/arrow-functions-parenless/input.js

@@ -0,0 +1,20 @@
+const y = 2;
+const f = (x) => x
+  |> (y => y + 1)
+  |> (z => z * y)
+
+const g = (x) => x
+  |> (y =>
+    y + 1
+    |> (z => z * y)
+  )
+
+const h = (x) => x
+  |> (y => (
+    y + 1
+    |> (z => z * y)
+  ))
+
+expect(f(1)).toBe(4);
+expect(g(1)).toBe(2);
+expect(h(1)).toBe(2);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/minimal/arrow-functions-parenless/output.js

@@ -0,0 +1,23 @@
+const y = 2;
+
+const f = x => {
+  var _z, _y;
+
+  return _z = (_y = x, _y + 1), _z * y;
+};
+
+const g = x => {
+  var _y2, _z2;
+
+  return _y2 = x, (_z2 = _y2 + 1, _z2 * _y2);
+};
+
+const h = x => {
+  var _y3, _z3;
+
+  return _y3 = x, (_z3 = _y3 + 1, _z3 * _y3);
+};
+
+expect(f(1)).toBe(4);
+expect(g(1)).toBe(2);
+expect(h(1)).toBe(2);

packages/babel-plugin-syntax-pipeline-operator/src/index.js

@@ -1,6 +1,6 @@
 import { declare } from "@babel/helper-plugin-utils";
 
-export const proposals = ["minimal", "smart"];
+export const proposals = ["minimal", "smart", "fsharp"];
 
 export default declare((api, { proposal }) => {
   api.assertVersion(7);