WIP: Transform for F# Pipeline

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

@@ -0,0 +1,56 @@
+import { types as t } from "@babel/core";
+
+// tries to optimize sequence expressions in the format
+//   (a = b, ((c) => d + e)(a))
+// to
+//   (a = b, a + e)
+const buildOptimizedSequenceExpression = ({ assign, call, path }) => {
+  const { left: placeholderNode, right: pipelineLeft } = assign;
+  const { callee: pipelineRight } = call;
+
+  let optimizeArrow =
+    t.isArrowFunctionExpression(pipelineRight) &&
+    t.isExpression(pipelineRight.body) &&
+    !pipelineRight.async &&
+    !pipelineRight.generator;
+  let param;
+
+  if (optimizeArrow) {
+    const { params } = pipelineRight;
+    if (params.length === 1 && t.isIdentifier(params[0])) {
+      param = params[0];
+    } else if (params.length > 0) {
+      optimizeArrow = false;
+    }
+  } else if (t.isIdentifier(pipelineRight, { name: "eval" })) {
+    const evalSequence = t.sequenceExpression([
+      t.numericLiteral(0),
+      pipelineRight,
+    ]);
+
+    call.callee = evalSequence;
+
+    return t.sequenceExpression([assign, call]);
+  } else if (
+    (t.isIdentifier(pipelineRight) &&
+      path.scope.hasBinding(pipelineRight.name)) ||
+    t.isImmutable(pipelineLeft)
+  ) {
+    return t.callExpression(pipelineRight, [pipelineLeft]);
+  }
+
+  if (optimizeArrow && !param) {
+    // Arrow function with 0 arguments
+    return t.sequenceExpression([pipelineLeft, pipelineRight.body]);
+  }
+
+  if (param) {
+    path.get("right").scope.rename(param.name, placeholderNode.name);
+
+    return t.sequenceExpression([assign, pipelineRight.body]);
+  }
+
+  return t.sequenceExpression([assign, call]);
+};
+
+export default buildOptimizedSequenceExpression;

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

@@ -0,0 +1,26 @@
+import { types as t } from "@babel/core";
+import buildOptimizedSequenceExpression from "./buildOptimizedSequenceExpression";
+
+const fsharpVisitor = {
+  BinaryExpression(path) {
+    const { scope, node } = path;
+    const { operator, left, right } = node;
+    if (operator !== "|>") return;
+
+    const placeholder = scope.generateUidIdentifierBasedOnNode(left);
+    scope.push({ id: placeholder });
+
+    const call =
+      right.type === "AwaitExpression"
+        ? t.awaitExpression(t.cloneNode(placeholder))
+        : t.callExpression(right, [t.cloneNode(placeholder)]);
+    const sequence = buildOptimizedSequenceExpression({
+      assign: t.assignmentExpression("=", t.cloneNode(placeholder), left),
+      call,
+      path,
+    });
+    path.replaceWith(sequence);
+  },
+};
+
+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/src/minimalVisitor.js

@@ -1,51 +1,22 @@
 import { types as t } from "@babel/core";
+import buildOptimizedSequenceExpression from "./buildOptimizedSequenceExpression";
 
 const minimalVisitor = {
   BinaryExpression(path) {
-    const { scope } = path;
-    const { node } = path;
-    const { operator, left } = node;
-    let { right } = node;
+    const { scope, node } = path;
+    const { operator, left, 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);
+    const placeholder = scope.generateUidIdentifierBasedOnNode(left);
     scope.push({ id: placeholder });
-    if (param) {
-      path.get("right").scope.rename(param.name, placeholder.name);
-    }
 
-    const call = optimizeArrow
-      ? right.body
-      : t.callExpression(right, [t.cloneNode(placeholder)]);
+    const call = t.callExpression(right, [t.cloneNode(placeholder)]);
     path.replaceWith(
-      t.sequenceExpression([
-        t.assignmentExpression("=", t.cloneNode(placeholder), left),
+      buildOptimizedSequenceExpression({
+        assign: t.assignmentExpression("=", t.cloneNode(placeholder), left),
         call,
-      ]),
+        path,
+      }),
     );
   },
 };

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

@@ -0,0 +1,27 @@
+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 _ref, _ref2, _ref3;
+
+var result = (_ref = (_ref2 = (_ref3 = [5, 10], _ref3.map(x => x * 2)), _ref2.reduce((a, b) => a + b)), _ref + 1);
+expect(result).toBe(31);
+
+var inc = x => x + 1;
+
+var double = x => x * 2;
+
+var result2 = [4, 9].map(x => {
+  var _ref4, _x;
+
+  return double(inc(x));
+});
+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(inc(10)).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/multiple-argument-use/input.js

@@ -0,0 +1,5 @@
+var array = [10,20,30];
+
+var last = array |> (a => a[a.length-1]);
+
+expect(last).toBe(30);

packages/babel-plugin-proposal-pipeline-operator/test/fixtures/fsharp/multiple-argument-use/output.js

@@ -0,0 +1,5 @@
+var _array;
+
+var array = [10, 20, 30];
+var last = (_array = array, _array[_array.length - 1]);
+expect(last).toBe(30);

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 +1,7 @@
+var _ref, _a;
+
+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);