Megatest

    (query
     (for-each-row
      (lambda (row)
	(let ((var  (car row))
	      (val  (cadr row)))
	  (hash-table-set! result var val))))
     (sql db "SELECT var,val FROM envvars AS a WHERE context=? AND val != (SELECT val FROM envvars WHERE var=a.var AND context=?)")
     contexta contextb)
     contextb contexta)
    result))

;;
(define (env:blind-merge l1 l2)
  (if (null? l1) l2
      (if (null? l2) l1
	  (cons (car l1) (cons (car l2) (env:blind-merge (cdr l1) (cdr l2)))))))