Document E063 and E160

Author: strager

docs/errors/E063.md

@@ -0,0 +1,19 @@
+# E063: missing operator between expression and arrow function
+
+The left-hand side of `=>` must be a list of parameters. It is a syntax error if
+the left-hand side looks like a function call:
+
+    let fs = require("fs");
+    let path = process.argv[2];
+    fs.readFile(path (err, data) => {
+      console.log(data);
+    });
+
+To fix this error, make the left-hand side of `=>` valid by adding an operator
+(usually `,`) before the parameter list:
+
+    let fs = require("fs");
+    let path = process.argv[2];
+    fs.readFile(path, (err, data) => {
+      console.log(data);
+    });

docs/errors/E160.md

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+# E160: unexpected '=>'; expected parameter for arrow function, but got an expression instead
+
+The left-hand side of `=>` must be a list of parameters. It is a syntax error if
+the left-hand side is instead an expression (such as a property access or a
+function call):
+
+    if (this.mapSize => this.capacity) {
+      throw new Error("too many items");
+    }
+
+    let fs = require("fs");
+    let path = process.argv[2];
+    fs.mkdir(path () => console.log("done"));
+
+To fix this error, replace `=>` with the intended operator, such as `>=`:
+
+    if (this.mapSize >= this.capacity) {
+      throw new Error("too many items");
+    }
+
+Alternatively, make the left-hand side of `=>` valid by adding an operator
+(usually `,`) before the parameter list:
+
+    let fs = require("fs");
+    let path = process.argv[2];
+    fs.mkdir(path, () => console.log("done"));