31 scheme/nest
| (require scheme/nest) |
Combines nested expressions that syntactically drift to the right into
a more linear textual format, much in the same way that let*
linearizes a sequence of nested let expressions.
For example,
(nest ([let ([x 10] [y 6])] [with-handlers ([exn:fail? (lambda (x) 15)])] [parameterize ([current-output-port (current-error-port)])] [let-values ([(d r) (quotient/remainder x y)])]) (display (+ d r)))
is equivalent to
(let ([x 10] [y 6]) (with-handlers ([exn:fail? (lambda (x) 15)]) (parameterize ([current-output-port (current-error-port)]) (let-values ([(d r) (quotient/remainder x y)]) (display (+ d r))))))
The nest form is unusual in that it has no semantics apart from its expansion, and its implementation is easier to understand than a precise prose description:
(define-syntax nest (syntax-rules () [(nest () body0 body ...) (let () body0 body ...)] [(nest ([form forms ...]) body0 body ...) (form forms ... (let () body0 body ...))] [(nest ([form forms ...] . more) body0 body ...) (form forms ... (nest more body0 body ...))]))