Read p5.strands callback params and body from the AST

src/strands/strands_transpiler.js

@@ -2013,17 +2013,19 @@ function runControlFlowPass(ast, uniformCallbackNames) {
 }
 
 function buildStrandsCallback(p5, ast, scope) {
-  const transpiledSource = escodegen.generate(ast);
   const scopeKeys = Object.keys(scope);
-  const match =
-    /\(?\s*(?:function)?\s*\w*\s*\(([^)]*)\)\s*(?:=>)?\s*{((?:.|\n)*)}\s*;?\s*\)?/.exec(
-      transpiledSource
-    );
-  if (!match) {
-    console.log(transpiledSource);
+  // Source is wrapped in parens before parsing, so the callback is the
+  // program's single expression. Read params/body from that node so
+  // `param => { ... }` works after escodegen drops the parentheses.
+  const fn = ast.body.length === 1 && ast.body[0].expression;
+  if (
+    !fn ||
+    (fn.type !== 'FunctionExpression' && fn.type !== 'ArrowFunctionExpression')
+  ) {
+    console.log(escodegen.generate(ast));
     throw new Error('Could not parse p5.strands function!');
   }
-  const params = match[1].split(/,\s*/).filter(param => !!param.trim());
+  const params = fn.params.map(param => escodegen.generate(param));
   let paramVals, paramNames;
   if (params.length > 0) {
     paramNames = params;
@@ -2032,7 +2034,10 @@ function buildStrandsCallback(p5, ast, scope) {
     paramNames = scopeKeys;
     paramVals = scopeKeys.map(key => scope[key]);
   }
-  const body = match[2];
+  const body =
+    fn.body.type === 'BlockStatement'
+      ? fn.body.body.map(statement => escodegen.generate(statement)).join('\n')
+      : `return ${escodegen.generate(fn.body)};`;
   try {
     const internalStrandsCallback = new Function('__p5', ...paramNames, body);
     // Create a parameter called __p5, not just p5, because users of instance mode

test/unit/webgl/p5.Shader.js

@@ -506,6 +506,26 @@ suite('p5.Shader', function () {
       }).not.toThrowError();
     });
 
+    test('accepts an arrow function with an unparenthesized parameter', () => {
+      myp5.createCanvas(5, 5, myp5.WEBGL);
+      expect(() => {
+        // Source text, so this does not depend on how the test file is transformed.
+        const myShader = myp5.buildMaterialShader(
+          `param => {
+            const { myp5 } = param;
+            myp5.getPixelInputs(inputs => {
+              inputs.color = [1, 0, 0, 1];
+              return inputs;
+            });
+          }`,
+          { myp5 }
+        );
+        myp5.noStroke();
+        myp5.shader(myShader);
+        myp5.plane(myp5.width, myp5.height);
+      }).not.toThrowError();
+    });
+
     test('buildMaterialShader forwards scope to modify', () => {
       myp5.createCanvas(5, 5, myp5.WEBGL);
       expect(() => {