The REPL in DrScheme is transparent (as described in the DrScheme paper). This
avoids subtle history-induced errors and
misunderstandings. DrScheme's REPL avoids
these problems in two ways:
Every time the user clicks Execute,
DrScheme erases all internal state
associated with the REPL.
DrScheme warns users when
they make changes, do not click Execute, and
evaluate expressions in the REPL.
