Change the eval_all function (which is called from do_begin_form) to complete the implementation of the begin special form. A begin expression is evaluated by evaluating all sub-expressions in order. The value of the begin expression is the value of the final sub-expression. scm> (begin (+ 2 3) (+ 5 6))
11
scm> (define x (begin (display 3) (newline) (+ 2 3)))
3
x
scm> (+ x 3)
8
scm> (begin (print 3) '(+ 2 3))
3
(+ 2 3)
If eval_all is passed an empty list of expressions (nil), then it should return the Python value None, which represents an undefined Scheme value.
CODE:
def eval_all(expressions, env):
"""Evaluate each expression in the Scheme list EXPRESSIONS in
environment ENV and return the value of the last."""
# BEGIN PROBLEM 8
return scheme_eval(expressions. first, env)
# END PROBLEM 8