commit 5e450b0737e5c3175b1bfc4616185c7a8d2687e2
parent ba141e50e66069d5ca9ada2345d5a4a65281a12a
Author: Greg Hendershott <greghendershott@gmail.com>
Date: Tue, 13 Nov 2012 13:05:26 -0500
Various edits
Diffstat:
| M | main.rkt | | | 35 | +++++++++++++++++++++-------------- |
1 file changed, 21 insertions(+), 14 deletions(-)
diff --git a/main.rkt b/main.rkt
@@ -845,7 +845,7 @@ Next, some shortcuts.
Instead of an additional, nested @racket[syntax-case], we could use
@racket[with-syntax]@margin-note*{Another name for
-@racket[with-syntax] could be, "define pattern variable".}. This
+@racket[with-syntax] could be, "with new pattern variable".}. This
rearranges the @racket[syntax-case] to look more like a @racket[let]
statement---first the name, then the value. Also it's more convenient
if we need to define more than one pattern variable.
@@ -864,40 +864,47 @@ if we need to define more than one pattern variable.
(foo-bar)
]
+Again, @racket[with-syntax] is simply @racket[syntax-case] rearranged:
+
+@racketblock[
+(syntax-case #,(italic "<syntax>") () [#,(bold "<pattern>") <body>])
+(with-syntax ([#,(bold "<pattern>") #,(italic "<syntax>")]) <body>)
+]
+
Whether you use an additional @racket[syntax-case] or use
-@racket[with-syntax], either way you are simply defining an additional
-pattern variable. Don't let the terminology and structure make it seem
-mysterious.
+@racket[with-syntax], either way you are simply defining additional
+pattern variables. Don't let the terminology and structure make it
+seem mysterious.
@subsubsection{@racket[with-syntax*]}
-We may recall that @racket[let] doesn't let us use a definition in a
-subsequent clause:
+We know that @racket[let] doesn't let us use a binding in a subsequent
+one:
@i[
(let ([a 0]
[b a])
- (values a b))
+ b)
]
-We could nest @racket[let]s:
+Instead we can nest @racket[let]s:
@i[
(let ([a 0])
(let ([b a])
- (values a b)))
+ b))
]
-Or we could use @racket[let*]:
+Or use a shorthand for nesting, @racket[let*]:
@i[
(let* ([a 0]
- [b 0])
- (values a b))
+ [b a])
+ b)
]
-Similarly there is a @racket[with-syntax*] variation of
-@racket[with-syntax]:
+Similarly, instead of writing nested @racket[with-syntax]s, we can use
+@racket[with-syntax*]:
@i[
(require (for-syntax racket/syntax))
