(define (interpolate location *vars* text)
  (irregex-replace/all
   (irregex '(seq "${" (=> expr (+ (~ ("}")))) "}"))
   text
   (lambda (m)
     (let ((expr (irregex-match-substring m 'expr)))
       (cond
        ((string=? expr "$")
         "$")
        ((hash-table-exists? *vars* expr)
         (hash-table-ref *vars* expr))
        (else
         (error (sprintf "Undefined variable ${~a} in ~a" expr location))))))))