8.12
3.1 Writing Simple Macros with mischief/shorthand
| (require mischief/shorthand) | package: mischief-dev |
syntax
(define-shorthand (id . pattern) template)
(define-shorthand id [pattern template] ...)
Defines id as a macro that matches applications against each
pattern and produces the corresponding template for the first
match. Non-identifier macros with only a single pattern can use the simplified
form that combines the pattern with the macro name. Each pattern is
interpreted as in syntax-parse.
Examples:
> (define-shorthand (lam x e) (lambda {x} e))
> (define-shorthand def [(_ x:id e) (define x e)] [(_ (f x) e) (def f (lam x e))]) > (def (len seq) (for/fold {[n 0]} {[x seq]} (add1 n))) > (len (list 1 2 3)) 3
> (len (vector 1 2 3)) 3
syntax
(define-id-shorthand name template)
Defines name as an identifier macro that expands by replacing
name with template.
Examples:
> (define counter (box 0)) > (define-id-shorthand current (unbox counter))
> (define-id-shorthand increment! (set-box! counter (add1 current))) > current 0
> increment! > current 1
> increment! > current 2
> (current 'bad 'application) application: not a procedure;
expected a procedure that can be applied to arguments
given: 2
syntax
(define-alias id target-id)
syntax
(define-aliases [id target-id] ...)
Examples:
> (define-alias value quote) > (define-aliases [choose cond] [otherwise else])
> (define (sum xs) (choose [(empty? xs) (value 0)] [otherwise (+ (first xs) (sum (rest xs)))])) > (sum (list 1 2 3 4)) 10
syntax
(with-aliases {[id target-id] ...} body ...+)
Defines each id as a local alias for the corresponding
target-id within the body of the expression.
Examples:
> (with-aliases {[cake pi]} (* cake 2)) 6.283185307179586
> cake cake: undefined;
cannot reference an identifier before its definition
in module: 'program