From b953b448bae8c6e742239347db81a1f2edabdc41 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Thu, 21 Feb 2008 13:30:25 +0000
Subject: [PATCH] expose struct:struct-info

svn: r8753
---
 collects/scheme/private/struct-info.ss      | 24 ++++++++++-----------
 collects/scribblings/reference/struct.scrbl | 12 +++++++++--
 2 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/collects/scheme/private/struct-info.ss b/collects/scheme/private/struct-info.ss
index 2f15551198..16e38f8f47 100644
--- a/collects/scheme/private/struct-info.ss
+++ b/collects/scheme/private/struct-info.ss
@@ -7,9 +7,10 @@
 
   (#%provide make-struct-info
              struct-info?
-             extract-struct-info)
+             extract-struct-info
+             struct:struct-info)
   
-  (define-values (struct:struct-info create-struct-info struct-info-rec?
+  (define-values (struct:struct-info make-struct-info struct-info-rec?
                                      struct-info-ref struct-info-set!)
     (make-struct-type 'struct-info #f
                       1 0 #f
@@ -18,16 +19,15 @@
                         (raise-syntax-error
                          #f
                          "identifier for static struct-type information cannot be used as an expression"
-                         stx))))
-
-  (define-values (make-struct-info)
-    (lambda (proc)
-      (if (and (procedure? proc)
-               (procedure-arity-includes? proc 0))
-          (create-struct-info proc)
-          (raise-type-error 'make-struct-info
-                            "procedure (arity 0)"
-                            proc))))
+                         stx))
+                      null
+                      (lambda (proc info)
+                        (if (and (procedure? proc)
+                                 (procedure-arity-includes? proc 0))
+                            proc
+                            (raise-type-error 'make-struct-info
+                                              "procedure (arity 0)"
+                                              proc)))))
 
   (define-values (extract-struct-info)
     (lambda (si)
diff --git a/collects/scribblings/reference/struct.scrbl b/collects/scribblings/reference/struct.scrbl
index 743ba7d28b..1ba88a3231 100644
--- a/collects/scribblings/reference/struct.scrbl
+++ b/collects/scribblings/reference/struct.scrbl
@@ -361,8 +361,8 @@ information can be used during the expansion of other expressions via
 @scheme[syntax-local-value].
 
 For example, the @scheme[define-struct] variant for subtypes uses the
-base type name @scheme[t] to find the variable
-@scheme[struct@scheme[:t]] containing the base type's descriptor; it
+base type name @scheme[_t] to find the variable
+@schemeidfont{struct:}@scheme[_t] containing the base type's descriptor; it
 also folds the field accessor and mutator information for the base
 type into the information for the subtype. As another example, the
 @scheme[match] form uses a type name to find the predicates and field
@@ -449,3 +449,11 @@ form.}
 
 Extracts the list form of the structure type information represented
 by @scheme[v].}
+
+@defthing[struct:struct-info struct-type?]{
+
+The @tech{structure type descriptor} for the structure type returned
+by @scheme[make-struct-info]. This @tech{structure type descriptor} is
+mostly useful for creating structure subtypes. The structure type
+includes a guard that checks an instance's first field in the same way
+as @scheme[make-struct-info].}