~mc28/labs/evaluators/micro-scheme.scmand use the ``Execute'' button to evaluate all the definitions in that file. This file contains the Micro-Scheme implementation from section 10.3 of the text, along with some necessary definitions from section 10.2 and earlier chapters of the text.
(read-eval-print-loop)in Scheme and then try evaluating various Micro-Scheme expressions in the resulting Micro-Scheme read-eval-print loop. When you are done trying out Micro-Scheme and want to return to real Scheme, you can use the ``Break'' button at the top of the window.
look-up-value, as described in exercises 10.11 and 10.12 on page 299 of the textbook. You should use the ``Copy'' and ``Paste'' commands in Dr. Scheme to copy the definition of
look-up-valueinto your own file before you start modifying it. For 10.11, you could add
null?, so that you can do list processing in Micro-Scheme. For 10.12, you can add anything you've wished Scheme had built in, perhaps
square. Try out Micro-Scheme again, making sure that your new pre-defined names work.
withexpressions to Micro-Scheme. This will involve modifying the definition of
micro-scheme-parsing-p/a-list, so you should copy and paste that definition into your file as well. You shouldn't need to modify any other existing definitions -- you should just modify your copy of
micro-scheme-parsing-p/a-listand add any new definitions you need.
Here are two somewhat tricky
with expressions; think carefully
about what the value of each of them should be, and make sure your
implementation produces those values:
(with x = (+ 2 3) compute (with y = (+ x 4) compute (* x y))) (with x = (+ 2 3) compute (with x = (+ x 4) compute (* x x)))
Be sure to try to test every change to the code you make as soon as
possible. This way, if there is a bug, you'll know exactly where to
look. For this exercise, for example, you first may wish to make a
pattern/action for the
with statement that
allows you to test the pattern matching, before concerning yourself
with how these expressions should actually be turned into ASTs. In
particular, you can temporarily use the following action:
(lambda (variable value-expression body) (display "with expression parsed with variable ") (write variable) (display ", value expression ") (write value-expression) (display ", and body ") (write body) (newline) (make-constant-ast 7))This will of course not behave at all as with expressions should: it will make all with expressions always evaluate to 7. However, this "testing stub" will allow you to see that with expressions are being correctly pattern matched. Once you have checked that, you can replace the action with a real one.
~mc28/labs/evaluators/mini-scheme.scmand use the "Save Definitions As..." command to save a private copy in your own directory, which you will modify in the subsequent exercises. This file contains the definitions from section 10.4, with the exception of those superseded in section 10.5, and it also contains relevant definitions from 10.3 and earlier chapters. Finally, this file also contains the definitions from section 10.5 of
blank-line-at(p. 321), and
Note that you won't be able to run
mini-scheme until you
have completed the following two portions of the lab.
evaluate-in-at(page 322) which is commented out of the bottom of the file
Since you are supposed to show the value among other things of procedure ASTs (i.e., lambda expressions), be sure that your test involves some lambda expressions.