Initial ES modules support

lib/stdlib/prelude.js

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+// The prelude: its exports are the global names of every module, such as
+// `String` or `console`. A module that does not declare a name, and does not
+// import it, refers to the prelude's export of that name. A module can declare
+// a binding of the same name, which hides it (see compiler/src/link.rs)
+//
+// The stdlib is built on the natives in compiler/src/native.rs, the common
+// layer of operations on primitive values, which `jsrt:native` exports. The
+// compiler's own code for operators (`+` on strings and so on) uses the runtime
+// directly, not these functions.
+//
+// Restrictions:
+// - The prototypes of `String`, `Number`, `Boolean` and `Array` are fixed:
+//   the compiler reads them as the prelude's exports, as the prototypes of the
+//   primitives and of arrays. User code may not change them (no monkey-patching)
+// - `new String(x)`, `new Number(x)` and `new Boolean(x)` (wrapper objects) are
+//   not supported. These functions only convert
+// - A global name cannot be assigned to
+//
+// `String.prototype.concat` is not here, because it needs rest params, which
+// need arrays. `console.log` prints one arg only, for the same reason
+//
+// The natives are global names too, as the runtime's own fns, with `__pending`,
+// where an IO op's callback waits for the host (see loop.js). The compiler
+// needs `jsrt:coroutine` for async fns and generators, so the prelude loads it.
+// It finds the host's `__complete` in `jsrt:loop`
+//
+// The modules run in the order of these imports, before any other module
+
+export { undefined, NaN, Infinity } from "jsrt:globals";
+export { Object } from "jsrt:object";
+export { String } from "jsrt:string";
+export { Number } from "jsrt:number";
+export { Boolean } from "jsrt:boolean";
+export { Array } from "jsrt:array";
+export { Promise, queueMicrotask } from "jsrt:promise";
+export { setTimeout, clearTimeout } from "jsrt:timers";
+export { fs } from "jsrt:io";
+export { console } from "jsrt:console";
+export * from "jsrt:native";
+export { __pending } from "jsrt:loop";
+
+import "jsrt:coroutine";