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65 | Compatibility Executables

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nest

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### 31`` scheme/nest

( require scheme/nest )

(nest ([datum ...+] ...) body ...+)

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 ...))]))

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