call-with-environment-variables

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call-with-environment-variables

Set up and take down environment vars

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call-with-environment-variables
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call-with-environment-variables

call-with-environment-variables variables thunkprocedure

Sets up environment variable via dynamic-wind which are taken down after thunk.

variables: An alist of the form '(("var" . "value") ...)
thunk: The thunk to execute with a modified environment

(define (call-with-environment-variables variables thunk)
  (let ((pre-existing-variables
          (map (lambda (var-value)
                 (let ((var (car var-value)))
                   (cons var (get-environment-variable var))))
               variables)))
    (dynamic-wind
      (lambda () (void))
      (lambda ()
        (use posix)
        (for-each
          (lambda (var-value) (setenv (car var-value) (cdr var-value)))
          variables)
        (thunk))
      (lambda ()
        (for-each
          (lambda (var-value)
            (let ((var (car var-value)) (value (cdr var-value)))
              (if value (setenv var value) (unsetenv var))))
          pre-existing-variables)))))