rebirth: Add `eval'

* build-aux/bootstrap/rebirth.scm: Provide env to `rebirth->ecmascript-prog'.
  (rebirth->ecmascript-prog)[env-es]: New param.  Use for `_env' in
    generated self-executing ES function.
  (es:empty-env): New procedure.
* build-aux/bootstrap/rebirth/es.scm (es:raw): Remove unused macro.
  (es:envf)[env]: New parameter.  Use in place of hard-coded inherited env.
  (es:inherit-env): New procedure, extracted from proceeding.
  (lambda, let): Use it.
  (null-environment, eval): New procedures.

build-aux/bootstrap/rebirth.scm

@@ -844,15 +844,20 @@
 ;; This compiles the AST into ECMAScript using `rebirth->ecmascript' and
 ;; then wraps it in a self-executing function to limit scope and create the
 ;; toplevel environment.
-(define (rebirth->ecmascript-prog ast)
+(define (rebirth->ecmascript-prog ast env-es)
   ;; (note that we no longer depend on libprebirth)
   (string-append "(function(_env){"
                  (rebirth->ecmascript ast)
-                 "})({macros:{}});"))
+                 "})(" env-es ");"))
+
+;; An empty environment.
+(define (es:empty-env)
+  "{macros:{}}")
 
 
 ;; at this point, this program can parse itself and output a CST (sans
 ;; whitespace)
 (es:console (rebirth->ecmascript-prog
              (parse-lisp
-              (es:file->string "/dev/stdin"))))
+              (es:file->string "/dev/stdin"))
+             (es:empty-env)))

build-aux/bootstrap/rebirth/es.scm

@@ -79,20 +79,18 @@
    (define-macro (es:error . args)
      (`quote (%es:native-apply console.error (unquote@ args))))
 
-   (define-macro (es:raw . body)
-     (`quote
-      (string->es (unquote@ body))))
-
-   ;; Expand the body BODY into a new environment inherited from the current
-   ;; environment.  Environments are currently handled by the ES runtime, so
-   ;; this is easy.
-   (define-macro (es:envf . body)
+   ;; Expand the body BODY into a new environment.  Environments are
+   ;; currently handled by the ES runtime, so this is easy.
+   (define-macro (es:envf env . body)
      (`quote
       (string-append
        "(function(_env){"
        "return "
        (unquote@ body)
-       "})(Object.create(_env))")))
+       "})(" (unquote env) ")")))
+
+   (define (es:inherit-env)
+     "Object.create(_env)")
 
    (define-macro (define-es-macro decl . body)
      (quasiquote
@@ -116,7 +114,7 @@
      "__whilebrk=true")
 
    (define-es-macro (lambda fnargs . body)
-     (es:envf
+     (es:envf (es:inherit-env)
       "function(" (join ", " (map tparam->es fnargs)) "){\n"
       (env-params fnargs)
       (body->es body #t)
@@ -138,7 +136,7 @@
             (fparams (join ", " (map tparam->es params)))
             (args    (map cadr bindings))
             (fargs   (map sexp->es args)))
-       (string-append (es:envf
+       (string-append (es:envf (es:inherit-env)
                        "(function(" fparams "){\n"
                        (env-params params)
                        (body->es body #t) "\n"
@@ -199,6 +197,23 @@
      (`quote (let () (unquote@ exprs))))
 
 
+   ;; This doesn't currently produce any sort of encapsulated
+   ;; environment---it just produces an ECMAScript string.  This also
+   ;; does not provide any of the expected syntatic keywords yet.
+   (define (null-environment version)
+     (if (not (eq? version 5))
+         (error "null-environment version must be 5")
+         (es:empty-env)))
+
+   ;; `eval' re-uses the macro `list->ast' procedure, immediately applying
+   ;; its result.
+   (define-macro (eval expr env)
+     (`quote (%es:native-apply
+              eval
+              (es:envf (unquote env)
+                       (sexp->es (list->ast (unquote expr)))))))
+
+
    ;; We unfortunately have to worry about environment mutability in the
    ;; current implementation.  Since variables within environments are
    ;; implemented using ECMAScript's prototype chain, any sets affect the