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 ...))])) |