replaced at-syntax with syntax-local-eval

svn: r17168

collects/scheme/private/at-syntax.ss

@@ -1,71 +0,0 @@
-#lang scheme/base
-
-(require (for-template scheme/base))
-
-(provide at-syntax)
-
-;; -------------------------------------------------------------------
-;; NOTE: This library is for internal use only, it is can change
-;; and/or disappear.  Do not use without protective eyewear!
-;; -------------------------------------------------------------------
-
-#|
-
-The `(at-syntax expr)' form is a useful syntax-time utility that can
-be used to sort of evaluate an expression at syntax time, and doing so
-in a well behaved way (eg, it respects the source for-syntax bindings,
-but it does have some issues).  It can be used to implement an escape
-to the syntax level that is not restricted like `begin-for-syntax'.
-
-The basic idea of the code is to plant the given expression on the
-right hand side of a `let-syntax' -- inside a `(lambda (stx) ...)'  to
-make it a valid transformer, with a singe use of this macro so that we
-get it to execute with `local-expand'.  The macro returns a 3d
-expression that contains the evaluated expression "somehwhere",
-depending on the expansion of `let-syntax' -- so to make it easy to
-find we plant it inside a thunk (so this works as long as `let-syntax'
-does not include 3d procedure values in its expansion).  Finally, the
-constructed `let-syntax' is expanded, we search through the resulting
-syntax for the thunk, then apply it to get the desired value.
-
-Here's a silly example to demonstrate:
-
-  > (define-syntax (compile-time-if stx)
-      (syntax-case stx ()
-        [(_ cond expr1 expr2)
-         (if (at-syntax #'cond) #'expr1 #'expr2)]))
-  > (define-for-syntax x 8)
-  > (define x 100)
-  > (compile-time-if (< x 10) (+ x 10) (- x 10))
-  110
-
-And another example, creating a macro for syntax-time expressions:
-
-  > (define-syntax (compile-time-value stx)
-      (syntax-case stx ()
-        [(_ expr) #`(quote #,(at-syntax #'expr))]))
-  > (compile-time-value (* x 2))
-  16
-
-but the `quote' here is a hint that this can get 3d values into
-syntax, and all the problems that are involved.  Also, note that it
-even works if you try to do something like:
-
-  > (compile-time-value (begin (set! x 11) x))
-  11
-
-(but, of course, it cannot be used to define new bindings).
-
-|#
-
-(define (at-syntax expr)
-  (let loop ([x (with-syntax ([e expr])
-                  (local-expand
-                   #'(let-syntax ([here (lambda (stx)
-                                          (datum->syntax stx (lambda () e)))])
-                       here)
-                   'expression '()))])
-    (cond [(procedure? x) (x)]
-          [(pair? x) (or (loop (car x)) (loop (cdr x)))]
-          [(syntax? x) (loop (syntax-e x))]
-          [else #f])))

collects/scheme/provide.ss

@@ -1,7 +1,7 @@
 #lang scheme/base
 
 (require (for-syntax scheme/base scheme/provide-transform scheme/list
-                     "private/at-syntax.ss"))
+                     (only-in unstable/syntax syntax-local-eval)))
 
 (provide matching-identifiers-out)
 (define-syntax matching-identifiers-out
@@ -21,7 +21,7 @@
    (lambda (stx modes)
      (syntax-case stx ()
        [(_ proc spec)
-        (let ([proc (at-syntax #'proc)])
+        (let ([proc (syntax-local-eval #'proc)])
           (filter-map
            (lambda (e)
              (let* ([s1 (symbol->string (export-out-sym e))]

collects/scheme/require.ss

@@ -1,7 +1,7 @@
 #lang scheme/base
 
 (require (for-syntax scheme/base scheme/require-transform scheme/list
-                     "private/at-syntax.ss")
+                     (only-in unstable/syntax syntax-local-eval))
          "require-syntax.ss")
 
 (provide matching-identifiers-in)
@@ -43,7 +43,7 @@
    (lambda (stx)
      (syntax-case stx ()
        [(_ proc spec)
-        (let ([proc (at-syntax #'proc)])
+        (let ([proc (syntax-local-eval #'proc)])
           (define-values [imports sources] (expand-import #'spec))
           (values
            (filter-map

collects/unstable/syntax.ss

@@ -4,7 +4,8 @@
          syntax/stx
          unstable/struct
          (for-syntax scheme/base
-                     scheme/private/sc))
+                     scheme/private/sc)
+         (for-template scheme/base))
 
 (provide unwrap-syntax