From 954e850e209771e2516456e7e563c5d0f3c08f77 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Thu, 1 Oct 2009 21:14:21 +0000
Subject: [PATCH] fix reference (restoring some text that was lost in the
 reference-manual rewrite) to describe the problem with macro-introduced
 bindings and the top level

svn: r16205
---
 .../scribblings/reference/syntax-model.scrbl  | 114 +++++++++++++++++-
 collects/scribblings/reference/syntax.scrbl   |   9 +-
 2 files changed, 119 insertions(+), 4 deletions(-)

diff --git a/collects/scribblings/reference/syntax-model.scrbl b/collects/scribblings/reference/syntax-model.scrbl
index 2060d83dc3..f5c15c9fe3 100644
--- a/collects/scribblings/reference/syntax-model.scrbl
+++ b/collects/scribblings/reference/syntax-model.scrbl
@@ -3,6 +3,9 @@
           (for-syntax mzscheme)
           "mz.ss")
 
+@(define scheme-eval (make-base-eval))
+@(interaction-eval #:eval scheme-eval (require (for-syntax scheme/base)))
+
 @;------------------------------------------------------------------------
 @title[#:tag "syntax-model"]{Syntax Model}
 
@@ -447,7 +450,7 @@ core syntactic forms are encountered:
        right-hand-side expressions are also extended with the
        bindings.}
 
- @item{Definitions in @scheme[internal-definition contexts] introduce
+ @item{Definitions in @tech{internal-definition contexts} introduce
        bindings as described in @secref["intdef-body"].}
 
 ]
@@ -600,7 +603,7 @@ then expansion stops without adding the identifier.
 @;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 @subsection[#:tag "intdef-body"]{Internal Definitions}
 
-An internal-definition context corresponds to a partial expansion step
+An @tech{internal-definition context} corresponds to a partial expansion step
 (see @secref["partial-expansion"]). A form that supports internal
 definitions starts by expanding its first form in an
 internal-definition context, but only partially. That is, it
@@ -692,6 +695,109 @@ module is attached to a namespace through
 are transitively attached, but instances are attached only at
 phases at or below the namespace's @tech{base phase}.
 
+@;------------------------------------------------------------------------
+@subsection[#:tag "macro-introduced-bindings"]{Macro-Introduced Bindings}
+
+When a top-level definition binds an identifier that originates from a
+ macro expansion, the definition captures only uses of the identifier
+ that are generated by the same expansion. This behavior is consistent
+ with expansion in @tech{internal-definition contexts}, where the
+ defined identifier turns into a fresh lexical binding.
+
+@examples[
+(define-syntax def-and-use-of-x
+  (syntax-rules ()
+    [(def-and-use-of-x val)
+     (code:comment @#,t{@scheme[x] below originates from this macro:})
+     (begin (define x val) x)]))
+(define x 1)
+x
+(def-and-use-of-x 2)
+x
+
+(define-syntax def-and-use
+  (syntax-rules ()
+    [(def-and-use x val)
+     (code:comment @#,t{@scheme{x} below was provided by the macro use:})
+     (begin (define x val) x)]))
+(def-and-use x 3)
+x
+]
+
+For a top-level definition (outside of a module), the order of
+ evaluation affects the binding of a generated definition for a
+ generated identifier use. If the use precedes the definition, then
+ the use refers to a non-generated binding, just as if the generated
+ definition were not present. (No such dependency on order occurs
+ within a module, since a module binding covers the entire module
+ body.) To support the declaration of an identifier before its use,
+ the @scheme[define-syntaxes] form avoids binding an identifier if the
+ body of the @scheme[define-syntaxes] declaration produces zero
+ results.
+
+@examples[
+#:eval scheme-eval
+(define bucket-1 0)
+(define bucket-2 0)
+(define-syntax def-and-set!-use-of-x
+  (syntax-rules ()
+    [(def-and-set!-use-of-x val)
+     (begin (set! bucket-1 x) (define x val) (set! bucket-2 x))]))
+(define x 1)
+(def-and-set!-use-of-x 2)
+x
+bucket-1
+bucket-2
+
+(define-syntax defs-and-uses/fail
+  (syntax-rules ()
+    [(def-and-use)
+     (begin
+      (code:comment @#,t{Initial reference to @scheme[even] precedes definition:})
+      (define (odd x) (if (zero? x) #f (even (sub1 x))))
+      (define (even x) (if (zero? x) #t (odd (sub1 x))))
+      (odd 17))]))
+(defs-and-uses/fail)
+     
+(define-syntax defs-and-uses
+  (syntax-rules ()
+    [(def-and-use)
+     (begin
+      (code:comment @#,t{Declare before definition via no-values @scheme[define-syntaxes]:})
+      (define-syntaxes (odd even) (values))
+      (define (odd x) (if (zero? x) #f (even (sub1 x))))
+      (define (even x) (if (zero? x) #t (odd (sub1 x))))
+      (odd 17))]))
+(defs-and-uses)
+]
+
+Macro-generated \scheme{require} and \scheme{provide}
+ clauses also introduce and reference generation-specific bindings:
+
+@itemize[
+
+ @item{In @scheme[require], for a @scheme[_require-spec] of the form
+ @scheme[(rename-in [_orig-id _bind-id])] or @scheme[(only-in
+ .... [_orig-id _bind-id])], the @scheme[_bind-id] is bound only for
+ uses of the identifier generated by the same macro expansion as
+ @scheme[_bind-id]. In @scheme[require] for other
+ @scheme[_require-spec]s, the generator of the @scheme[_require-spec]
+ determines the scope of the bindings.}
+
+ @item{In @scheme[provide], for a @scheme[_provide-spec] of the form
+ @scheme[_id], the exported identifier is the one that binds
+ @scheme[_id] within the module in a generator-specific way, but the
+ external name is the plain @scheme[_id]. The exceptions for
+ @scheme[all-except-out] are similarly determined in a
+ generator-specific way, as is the @scheme[_orig-id] binding of a
+ @scheme[rename-out] form, but plain identifiers are used for the
+ external names. For @scheme[all-defined-out], only identifiers with
+ definitions having the same generator as the
+ @scheme[(all-defined-out)] form are exported; the external name is
+ the plain identifier from the definition.}
+
+]
+
 @;------------------------------------------------------------------------
 @section[#:tag "compilation-model"]{Compilation}
 
@@ -860,3 +966,7 @@ When an inferred name is not available, but a source location is
 available, a name is constructed using the source location
 information. Inferred and property-assigned names are also available
 to syntax transformers, via @scheme[syntax-local-name].
+
+@;----------------------------------------
+
+@close-eval[scheme-eval]
diff --git a/collects/scribblings/reference/syntax.scrbl b/collects/scribblings/reference/syntax.scrbl
index 7e171cc41d..1f4f1d2861 100644
--- a/collects/scribblings/reference/syntax.scrbl
+++ b/collects/scribblings/reference/syntax.scrbl
@@ -1896,7 +1896,12 @@ expands to a definition of the first form where the @scheme[expr] is a
 Like @scheme[define-syntax], but creates a @tech{transformer binding}
 for each @scheme[id].  The @scheme[expr] should produce as many values
 as @scheme[id]s, and each value is bound to the corresponding
-@scheme[id]. }
+@scheme[id].
+
+When @scheme[expr] produces zero values for a top-level
+@scheme[define-syntaxes] (i.e., not in a module or internal-definition
+position), then the @scheme[id]s are effectively declared without
+binding; see @secref["macro-introduced-bindings"].
 
 @defexamples[#:eval (syntax-eval)
 (define-syntaxes (foo1 foo2 foo3)
@@ -1915,7 +1920,7 @@ as @scheme[id]s, and each value is bound to the corresponding
 (foo1)
 (foo2)
 (foo3)
-]
+]}
 
 @defform*[[(define-for-syntax id expr)
            (define-for-syntax (head args) body ...+)]]{