eval refitted

main.rkt

@@ -1,12 +1,62 @@
 #lang racket/base
 
-(require (for-syntax racket/base
+(require racket/string
+         (for-syntax racket/base
                      racket/list
                      racket/match
                      racket/string))
 
 (provide js js/expression)
 
+;; Convert a Racket value produced by (eval <racket-expr>) inside a js form to
+;; a JavaScript literal string.  This is a Racket -> JavaScript interpolation
+;; boundary, not JavaScript eval.
+(define (jsmaker-runtime-escape-js-string s)
+  (define out (open-output-string))
+  (for ([ch (in-string s)])
+    (case ch
+      [(#\\) (display "\\\\" out)]
+      [(#\") (display "\\\"" out)]
+      [(#\newline) (display "\\n" out)]
+      [(#\return) (display "\\r" out)]
+      [(#\tab) (display "\\t" out)]
+      [else (display ch out)]))
+  (get-output-string out))
+
+(define (jsmaker-runtime-js-string s)
+  (format "\"~a\"" (jsmaker-runtime-escape-js-string s)))
+
+(define (jsmaker-runtime-key->js k)
+  (jsmaker-runtime-js-string
+   (cond [(symbol? k) (symbol->string k)]
+         [(keyword? k) (keyword->string k)]
+         [(string? k) k]
+         [else (format "~a" k)])))
+
+(define (jsmaker-runtime-value->js v)
+  (cond
+    [(void? v) "undefined"]
+    [(eq? v #t) "true"]
+    [(eq? v #f) "false"]
+    [(number? v) (number->string v)]
+    [(string? v) (jsmaker-runtime-js-string v)]
+    [(char? v) (jsmaker-runtime-js-string (string v))]
+    [(symbol? v) (jsmaker-runtime-js-string (symbol->string v))]
+    [(keyword? v) (jsmaker-runtime-js-string (keyword->string v))]
+    [(null? v) "[]"]
+    [(pair? v)
+     (format "[~a]" (string-join (map jsmaker-runtime-value->js v) ", "))]
+    [(vector? v)
+     (format "[~a]" (string-join (map jsmaker-runtime-value->js (vector->list v)) ", "))]
+    [(hash? v)
+     (format "{~a}"
+             (string-join
+              (for/list ([(k val) (in-hash v)])
+                (format "~a: ~a" (jsmaker-runtime-key->js k) (jsmaker-runtime-value->js val)))
+              ", "))]
+    [else
+     (error 'js "cannot interpolate Racket value as JavaScript literal: ~e" v)]))
+
 ;; The js macro translates a practical Racket-expression subset to JavaScript.
 ;; It is intentionally syntax-driven: the Racket expressions are not evaluated.
 
@@ -201,6 +251,44 @@
     (set! tmp-counter (add1 tmp-counter))
     (format "__~a_~a" prefix tmp-counter))
 
+  ;; Runtime interpolation escape hatch.  Before compiling the syntax to a
+  ;; datum, the public macros replace each (eval <racket-expr>) subform by a
+  ;; unique placeholder symbol.  The generated macro result is then a Racket
+  ;; expression that replaces those placeholders by JavaScript literals computed
+  ;; from <racket-expr> in the use-site lexical context.  This is intentionally
+  ;; different from JavaScript eval, which remains available as
+  ;; (send window eval ...) or by binding/calling another identifier.
+  (define (compile-racket-eval expr)
+    (fail "internal eval placeholder; public macro should rewrite eval first" expr))
+
+  (define (replace-racket-evals stx)
+    (define counter 0)
+    (define evals '())
+    (define (fresh-eval-placeholder)
+      (set! counter (add1 counter))
+      (string->symbol (format "__rkt_eval_slot_~a__" counter)))
+    (define (walk d)
+      (match d
+        [(list 'quote _) d]
+        [(list 'quasiquote _) d]
+        [(list 'eval expr)
+         (define ph (fresh-eval-placeholder))
+         (set! evals (append evals (list (list (symbol->string ph) expr))))
+         ph]
+        [(? pair?) (cons (walk (car d)) (walk (cdr d)))]
+        [(? vector?) (list->vector (map walk (vector->list d)))]
+        [_ d]))
+    (values (walk (syntax->datum stx)) evals))
+
+  (define (wrap-compiled-js stx compiled evals)
+    (for/fold ([acc #`#,compiled]) ([ev (in-list evals)])
+      (define placeholder (first ev))
+      (define racket-expr-datum (second ev))
+      #`(string-replace #,acc
+                         #,placeholder
+                         (jsmaker-runtime-value->js
+                          #,(datum->syntax stx racket-expr-datum)))))
+
   ;; Racket conditionals treat only #f as false.  JavaScript would also
   ;; reject 0, "", null and undefined in condition position, so every
   ;; Racket test is compiled through this helper.
@@ -384,9 +472,22 @@
     (define content
       (case kind
         [(let)
-         ;; Evaluate all RHS expressions before introducing the JS let bindings.
-         ;; This avoids JavaScript TDZ bugs for Racket code such as
-         ;; (let ([x x]) ...), where the RHS must see the outer x.
+         ;; Racket let evaluates all RHS expressions before introducing the new
+         ;; bindings.  The common case can still be emitted directly when no RHS
+         ;; mentions one of the newly-bound identifiers.  If it does, use temps
+         ;; to avoid JavaScript TDZ bugs for code such as (let ([x x]) ...),
+         ;; where the RHS must see the outer x.
+         (define ids (map binding-id bindings))
+         (define (mentions-id? x id)
+           (cond
+             [(symbol? x) (eq? x id)]
+             [(pair? x) (or (mentions-id? (car x) id) (mentions-id? (cdr x) id))]
+             [(vector? x) (for/or ([e (in-vector x)]) (mentions-id? e id))]
+             [else #f]))
+         (define (mentions-any-bound-id? rhs)
+           (for/or ([id (in-list ids)]) (mentions-id? rhs id)))
+         (cond
+           [(for/or ([b (in-list bindings)]) (mentions-any-bound-id? (binding-rhs b)))
             (define tmps (for/list ([_ (in-list bindings)]) (fresh "let_value")))
             (define rhs-stmts
               (for/list ([tmp (in-list tmps)] [b (in-list bindings)])
@@ -395,6 +496,12 @@
               (for/list ([tmp (in-list tmps)] [b (in-list bindings)])
                 (format "let ~a = ~a;" (id->js (binding-id b)) tmp)))
             (join-lines (append rhs-stmts (list (block (join-lines (append bind-stmts (list (body-code))))))))]
+           [else
+            (join-lines
+             (append
+              (for/list ([b (in-list bindings)])
+                (format "let ~a = ~a;" (id->js (binding-id b)) (compile-expr (binding-rhs b))))
+              (list (body-code))))])]
         [(let*)
          ;; Emit the common case directly:
          ;;   (let* ([x 10] [y (+ x x)]) body)
@@ -1280,6 +1387,8 @@ if (~a !== false) return ~a;" tmp (compile-expr arg) tmp tmp)))
        (format "(~a = ~a)" (compile-assignment-target target) (compile-expr rhs))]
       [(list 'return) "undefined"]
       [(list 'return e) (compile-expr e)]
+      [(list 'eval racket-expr)
+       (compile-racket-eval racket-expr)]
       [(list f args ...) (compile-call f args)]
       [_ (literal->js d)]))
 
@@ -1289,9 +1398,11 @@ if (~a !== false) return ~a;" tmp (compile-expr arg) tmp tmp)))
 (define-syntax (js stx)
   (syntax-case stx ()
     [(_ form ...)
-     (datum->syntax stx (compile-top (syntax->datum #'(form ...))))]))
+     (let-values ([(clean-datum evals) (replace-racket-evals #'(form ...))])
+       (wrap-compiled-js stx (compile-top clean-datum) evals))]))
 
 (define-syntax (js/expression stx)
   (syntax-case stx ()
     [(_ form)
-     (datum->syntax stx (compile-expr (syntax->datum #'form)))]))
+     (let-values ([(clean-datum evals) (replace-racket-evals #'form)])
+       (wrap-compiled-js stx (compile-expr clean-datum) evals))]))

scrbl/jsmaker.scrbl

@@ -83,8 +83,11 @@ self-call.
 
 The generator is best understood as a source-to-source translator over syntax.
 The input is converted to datum form and matched against the supported surface
-language.  The Racket code is not evaluated.  This has a few important
-consequences:
+language.  The Racket code is normally not evaluated.  The deliberate exception
+is @racket[(eval racket-expr)], which interpolates a Racket value into the
+JavaScript source text.  The expression is evaluated in the lexical context of
+the @racket[js] or @racket[js/expression] use and its value is emitted as a
+JavaScript literal.  This has a few important consequences:
 
 @compact-items[
  @item{Only forms known to js-maker are translated specially.  Unknown calls are
@@ -100,6 +103,46 @@ consequences:
        helper functions/IIFEs to preserve semantics.}
 ]
 
+@subsection{Racket value interpolation with eval}
+
+The form @racket[(eval racket-expr)] is an interpolation escape hatch inherited
+from the original transformer.  It evaluates @racket[racket-expr] as Racket in
+the use-site lexical context and then splices the resulting value into the
+JavaScript source as a literal.  This makes surrounding Racket bindings visible
+to the interpolation expression.
+
+@(rkt+js
+#<<RKT
+(let ([x 10]
+      [y 20])
+  (js (let ([a (eval (* x y))])
+        (return (* a a)))))
+RKT
+#<<JS
+{
+  let a = 200;
+  return (a * a);
+}
+JS
+)
+
+@(rkt+js
+#<<RKT
+(js/expression (array (eval (+ 1 2))
+                      (eval (string-append "a" "b"))))
+RKT
+#<<JS
+[3, "ab"]
+JS
+)
+
+This is not JavaScript @tt{eval}.  To call JavaScript @tt{eval}, call the
+JavaScript function explicitly, for example @racket[(send window eval "1 + 2")].
+Racket-side @racket[eval] is best used for constants, generated literal data,
+and small configuration values that are known while the JavaScript source is
+being constructed.  It should not be used for run-time browser state, DOM access,
+or user input.
+
 @section{Supported expression and statement forms}
 
 The following Racket forms are supported as either expressions, statements, or
@@ -116,6 +159,7 @@ both, depending on context:
  @item{@racket[when], @racket[unless], @racket[while], @racket[for],
        @racket[for/list], @racket[for/vector], and @racket[for/fold].}
  @item{@racket[with-handlers] for the generic @racket[exn?] case.}
+ @item{@racket[(eval racket-expr)] for Racket-side value interpolation into JavaScript literals.}
  @item{Interop forms such as @racket[send], @racket[new], @racket[js-ref],
        @racket[js-dot], @racket[set-prop!], @racket[delete-prop!],
        @racket[js-delete], @racket[array], @racket[object],
@@ -732,14 +776,13 @@ harness rather than hiding raw JavaScript inside the feature implementation.
 
 @section{Further examples}
 
-The companion document @filepath{scrbl/usecases.scrbl} contains practical
-examples such as DOM manipulation, @tt{Set}, currying, object destructuring,
-timers, @tt{fetch}, sorting, binary search, and map-based counting.  Each use
-case shows the Racket/js-maker source, representative JavaScript output, and the
-behavior tested by the regression suite.
+The companion @hyperlink["../usecases/index.html"]{use-case manual} contains
+practical examples such as DOM manipulation, @tt{Set}, currying, object
+destructuring, timers, @tt{fetch}, sorting, binary search, and map-based
+counting.  Each use case shows the Racket/js-maker source, representative
+JavaScript output, and the behavior tested by the regression suite.
 
-When the documentation is rendered with @exec{raco scribble}, the use-case
-manual is normally emitted as a separate document next to this one.  The explicit
-file name is used here instead of a cross-document reference because the latter
+The source file for that companion manual is @filepath{scrbl/usecases.scrbl}.
+The relative link above is used instead of @racket[other-doc] because the latter
 can render as an unresolved @tt{(part ... "top")} tag when the two documents are
 built outside Racket's installed documentation index.

testing/jsmaker-regression.rkt

@@ -63,6 +63,24 @@
    (js-expression-test 'for-fold (js/expression (for/fold ([s 0]) ([x (in-list (list 1 2 3))]) (+ x s))) "6")
    (js-expression-test 'map-filter (js/expression (filter (lambda (x) (> x 2)) (map (lambda (x) (+ x 1)) (list 1 2 3)))) "[3,4]")
    (js-expression-test 'hash-ref (js/expression (hash-ref (hash 'a 1 'b 2) 'b)) "2")
+   (js-expression-test 'compile-time-eval-var
+                       (let ((x 10)
+                             (y 20))
+                         (js/expression (let ((a (eval (* x y))))
+                                          (+ a a))))
+                         "400")
+   (js-expression-test 'compile-time-eval-number
+                       (js/expression (eval (+ 1 2)))
+                       "3")
+   (js-expression-test 'compile-time-eval-data
+                       (js/expression (array (eval (list 1 2 3))
+                                             (eval (string-append "a" "b"))))
+                       "[[1,2,3],\"ab\"]")
+   (let ([x 10]
+         [y 20])
+     (js-expression-test 'runtime-eval-lexical-let
+                         (js/expression (let ([a (eval (* x y))]) (* a a)))
+                         "40000"))
    (js-expression-test 'substring (js/expression (substring "abcdef" 1 4)) "\"bcd\"")
    (js-expression-test 'equal-list (js/expression (equal? (list 1 2) (list 1 2))) "true")
    (js-expression-test 'cond-test-only (js/expression (cond [0] [else 2])) "0")