Removing uses of lambda in the web-server tutorial.

svn: r11283

collects/web-server/scribblings/tutorial/examples/model-2.ss

@@ -12,28 +12,29 @@
 ;; initialize-blog! : path? -> blog
 ;; Reads a blog from a path, if not present, returns default
 (define (initialize-blog! home)
-  (define the-blog
-    (with-handlers 
-        ([exn? (lambda (exn) 
-                 (make-blog
-                  (path->string home)
-                  (list (make-post "First Post" 
-                                   "This is my first post" 
-                                   (list "First comment!"))
-                        (make-post "Second Post" 
-                                   "This is another post"
-                                   (list)))))])
-      (with-input-from-file home
-        read)))
-  (set-blog-home! the-blog (path->string home))
-  the-blog)
+  (local [(define (log-missing-exn-handler exn)
+            (make-blog
+             (path->string home)
+             (list (make-post "First Post"
+                              "This is my first post"
+                              (list "First comment!"))
+                   (make-post "Second Post"
+                              "This is another post"
+                              (list)))))
+          (define the-blog
+            (with-handlers ([exn? log-missing-exn-handler])
+              (with-input-from-file home read)))]
+    (set-blog-home! the-blog (path->string home))
+    the-blog))
 
 ;; save-blog! : blog -> void
 ;; Saves the contents of a blog to its home
 (define (save-blog! a-blog)
-  (with-output-to-file (blog-home a-blog)
-    (lambda () (write a-blog))
-    #:exists 'replace))
+  (local [(define (write-to-blog)
+            (write a-blog))]
+    (with-output-to-file (blog-home a-blog) 
+      write-to-blog
+      #:exists 'replace)))
 
 ;; blog-insert-post!: blog string string -> void
 ;; Consumes a blog and a post, adds the post at the top of the blog.

collects/web-server/scribblings/tutorial/examples/model-3.ss

@@ -14,13 +14,12 @@
 (define (initialize-blog! home)
   (define db (sqlite:open home))
   (define the-blog (make-blog db))
-  (with-handlers ([exn? (lambda (exn) (void))])
-    (sqlite:exec/ignore
-     db 
-     (string-append
-      "CREATE TABLE posts "
-      "(id INTEGER PRIMARY KEY,"
-      "title TEXT, body TEXT)"))
+  (with-handlers ([exn? void])
+    (sqlite:exec/ignore db
+                        (string-append
+                         "CREATE TABLE posts "
+                         "(id INTEGER PRIMARY KEY,"
+                         "title TEXT, body TEXT)"))
     (blog-insert-post!
      the-blog "First Post" "This is my first post")
     (blog-insert-post!
@@ -35,12 +34,15 @@
 ;; blog-posts : blog -> (listof post?)
 ;; Queries for the post ids
 (define (blog-posts a-blog)
-  (map (compose (lambda (n) (make-post a-blog n))
-                string->number
-                (lambda (v) (vector-ref v 0)))
-       (rest (sqlite:select 
-              (blog-db a-blog)
-              "SELECT id FROM posts"))))
+  (local [(define (row->post a-row)
+            (make-post a-blog (string->number (vector-ref a-row 0))))
+          (define rows (sqlite:select
+                        (blog-db a-blog)
+                        "SELECT id FROM posts"))]
+    (cond [(empty? rows)
+           empty]
+          [else
+           (map row->post (rest rows))])))
 
 ;; post-title : post -> string?
 ;; Queries for the title
@@ -67,14 +69,15 @@
 ;; post-comments : post -> (listof string?)
 ;; Queries for the comments
 (define (post-comments p)
-  (with-handlers ([exn? (lambda _ empty)])
-    (map 
-     (lambda (v) (vector-ref v 0))
-     (rest 
-      (sqlite:select
-       (blog-db (post-blog p))
-       (format "SELECT content FROM comments WHERE pid = '~a'"
-               (post-id p)))))))
+  (local [(define (row->comment a-row)
+            (vector-ref a-row 0))
+          (define rows (sqlite:select
+                        (blog-db (post-blog p))
+                        (format "SELECT content FROM comments WHERE pid = '~a'"
+                                (post-id p))))]
+    (cond
+      [(empty? rows) empty]
+      [else (map row->comment (rest rows))])))
 
 ;; blog-insert-post!: blog? string? string? -> void
 ;; Consumes a blog and a post, adds the post at the top of the blog.

collects/web-server/scribblings/tutorial/tutorial.scrbl

@@ -812,21 +812,20 @@ Then, we'll make a function that allows our application to initialize the blog:
 @code:comment{initialize-blog! : path? -> blog}
 @code:comment{Reads a blog from a path, if not present, returns default}
 (define (initialize-blog! home)
-  (define the-blog
-    (with-handlers 
-        ([exn? (lambda (exn) 
-                 (make-blog
-                  (path->string home)
-                  (list (make-post "First Post" 
-                                   "This is my first post" 
-                                   (list "First comment!"))
-                        (make-post "Second Post" 
-                                   "This is another post"
-                                   (list)))))])
-      (with-input-from-file home
-        read)))
-  (set-blog-home! the-blog (path->string home))
-  the-blog)
+  (local [(define (log-missing-exn-handler exn)
+            (make-blog
+             (path->string home)
+             (list (make-post "First Post"
+                              "This is my first post"
+                              (list "First comment!"))
+                   (make-post "Second Post"
+                              "This is another post"
+                              (list)))))
+          (define the-blog
+            (with-handlers ([exn? log-missing-exn-handler])
+              (with-input-from-file home read)))]
+    (set-blog-home! the-blog (path->string home))
+    the-blog))
 ]
 
 @scheme[initialize-blog!] takes a path and tries to @scheme[read] from it. If the path contains
@@ -846,9 +845,11 @@ Next, we will need to write a function to save the model to the disk.
 @code:comment{save-blog! : blog -> void}
 @code:comment{Saves the contents of a blog to its home}
 (define (save-blog! a-blog)
-  (with-output-to-file (blog-home a-blog)
-    (lambda () (write a-blog))
-    #:exists 'replace))
+  (local [(define (write-to-blog)
+            (write a-blog))]
+    (with-output-to-file (blog-home a-blog) 
+      write-to-blog
+      #:exists 'replace)))
 ]
 
 @scheme[save-blog!] @scheme[write]s the model into its home .
@@ -987,7 +988,7 @@ We can now write the code to initialize a @scheme[blog] structure:
 (define (initialize-blog! home)
   (define db (sqlite:open home))
   (define the-blog (make-blog db))
-  (with-handlers ([exn? (lambda (exn) (void))])
+  (with-handlers ([exn? void])
     (sqlite:exec/ignore db
       (string-append
        "CREATE TABLE posts"
@@ -1059,11 +1060,15 @@ The only function that creates posts is @scheme[blog-posts]:
 @code:comment{blog-posts : blog -> (listof post?)}
 @code:comment{Queries for the post ids}
 (define (blog-posts a-blog)
-  (map (compose (lambda (n) (make-post a-blog n))
-                string->number
-                (lambda (v) (vector-ref v 0)))
-       (rest (sqlite:select (blog-db a-blog)
-                            "SELECT id FROM posts"))))
+  (local [(define (row->post a-row)
+            (make-post a-blog (string->number (vector-ref a-row 0))))
+          (define rows (sqlite:select
+                        (blog-db a-blog)
+                        "SELECT id FROM posts"))]
+    (cond [(empty? rows)
+           empty]
+          [else
+           (map row->post (rest rows))])))
 ]
 
 @scheme[sqlite:select] returns a list of vectors. The first element of the list is the name of the columns.