Egg:
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(define the-db-ctx (make-parameter #f)) ; '(<handle> . <alist>)

(define (initialise #!key db-ctx)
  (if db-ctx     (set! the-db-ctx db-ctx)))
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App:

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(use egg)

(define db-ctx (make-parameter))

(initialise db-ctx: db-ctx)

(db-ctx (open-database ...))

...

<(calls to the egg)>
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