ucsd-cse230-wi19 / hw3

Starter code for HW3

CSE 230 HW

Download

1. Use the fork link from the class website to create your private clone of the starter code.

2. Do git clone https://github.com/ucsd-cse230-wi19/hw3-XXX where XXX is your private repo.

Link to Upstream

3. Link your clone to the "upstream" to get any updates

$ make upstream

after this you can get "updates" (in case we modify the starter code), with

$ make update

Do the Assignment

4. Edit the files and run LH

$ make 

repeat this until LH says "SAFE"

Submit

5. Save (and submit) your work with:

$ git commit -a -m MESSAGE
$ git push

Hint on Q2

To implement full_asimp note that NAExp expressions look like:

Plus (Var x1) (Plus (Var x2) ... (Plus (Var xn) (N c)))

and the key is to write a function

plus_naexp :: NAExp -> NAExp -> NAExp 

which, when given two NAExps of the form

a1 = Plus (Var x1) (Plus (Var x2) ... (Plus (Var xn) (N c)))

a2 = Plus (Var y1) (Plus (Var y2) ... (Plus (Var ym) (N d)))

should essentially recursively go down the first expression till it hits the rightmost constant N c and replace it with a2-where-d-is-replaced with c+d.

To do the last step, you should write a function

cplus :: Int -> NAExp -> NAExp 

such that cplus n a recurses on a until it finds its rightmost constant c which is then replaced with n+c.

You should then use cplus to implement plus_naexp a1 a2 by recursively going inside a1 till you find its rightmost constant c which should then be replaced by cplus c a2.