commit 6eafcb7eda49489f62880da1f9de8d863d91af99
parent 8368cc56411d5526e1478ad9de2abe408f460335
Author: Jack Firth <jackhfirth@gmail.com>
Date: Tue, 9 Dec 2014 22:55:26 -0800
Update README.md
Fix code block formatting
Diffstat:
| M | README.md | | | 32 | ++++++++++++++++---------------- |
1 file changed, 16 insertions(+), 16 deletions(-)
diff --git a/README.md b/README.md
@@ -5,26 +5,26 @@ A Racket package for creating macros with built-in support for defining sub-macr
Sometimes complex Racket macros need a way for their syntax to be extended. The Racket match form is an example, new patterns can be created for match using define-match-expander. This racket package provides a form for defining a macro with the ability to define expanders for the macro. Consider this contrived example:
-(define-syntax call-each
- (syntax-parser
- [(_ f (expr ...))
- #'(begin (f expr) ...)]))
-
-(call-each displayln (1 2 3))
+ (define-syntax call-each
+ (syntax-parser
+ [(_ f (expr ...))
+ #'(begin (f expr) ...)]))
+
+ (call-each displayln (1 2 3))
If a user of this macro wished for a way to specify a range of numbers as the arguments, the user must define their own version of call-each with support for ranges that expands to using the original call-each. However, this racket package provides a form, define-syntax-with-expanders:
-(define-syntax-with-expanders call-each
- (syntax-parser
- [(_ f (expr ...))
- #'(begin (f expr) ... )]))
-
-(define-call-each-expander foo
- (syntax-parser
- [(_ low:number high:number)
- #`(#,@(range (syntax-e #'low) (syntax-e #'high)))]))
+ (define-syntax-with-expanders call-each
+ (syntax-parser
+ [(_ f (expr ...))
+ #'(begin (f expr) ... )]))
-(call-each displayln (foo 1 4))
+ (define-call-each-expander foo
+ (syntax-parser
+ [(_ low:number high:number)
+ #`(#,@(range (syntax-e #'low) (syntax-e #'high)))]))
+
+ (call-each displayln (foo 1 4))
The define-syntax-with-expanders form creates a define-call-each-expander form, which defines syntax transformers that are only used inside the body of a call-each form and expand before call-each does.
