CSE 341
Assignment 4: A Prolog Entree With a Haskell Appetizer

Remember: No late submissions will be accepted for this assignment!

No. 1 is a written question to be submitted on paper only (it must be typed---we can't grade what we can't read). For the remaining exercises, as usual, submit your code in one file named a4.pl electronically using turnin, and submit a printout of your code and test output (at least three usages of each predicate) in class.

1. Before we jump into Prolog, let's take a step back to cast a critical eye on Haskell. If you liked the way Haskell handled typing, concisely describe three distinct advantages of static typing with an inference system; if not, describe two disadvantages.

   This is no trick---both positions can be adequately defended by intelligent, eloquent computer scientists such as yourselves---so do not assume there's any one "right" answer. Your response should be no more than two or three paragraphs long and submitted on paper only. Type your answer, and use proper English exposition (e.g., no bulleted lists).

   Now, for the Prolog...

2. Write a predicate parity that takes a list whose elements are 1s or 0s and a 1 or 0 such that...
   • parity(List,1) succeeds iff the number of 1s in List is odd and
   • parity(List,0) succeeds iff the number of 1s in List is even.

   As you've probably guessed, you should assume that the given list contains only 1s and/or 0s (consider making this assumption explicit in the form of a comment in your code).

   example usages (edited SWI Prolog output):

   14 ?- parity([0,1],X).
   X = 1
         
   15 ?- parity([0,1,1,1,1,0],X).
   X = 0 
         
   16 ?- parity([0,1,1,1,1,0,1],X).
   X = 1 
   

3. In this exercise, you'll be writing two predicates to use with the database of relations shown below.

   The idea here is to write predicates that can be used to plan bus trips between locations by answering questions like "What bus do I take to get from [some location] to [elsewhere]?"

   More specifically, based on the busServes relation, you will define the following two predicates:

   • busConnects(Loc1,Loc2,BusNo) succeeds iff you can take Bus No. BusNo from Loc1 all the way to Loc2

   • busConnectsVia(Loc1,Loc2,Loc,BusNo1,BusNo2) succeeds iff you can take BusNo1 from Loc1 to Loc, then take BusNo2 to Loc2

   example usages (reformatted SWI Prolog output):

   2 ?- busServes(Bus,universityDistrict).
   Bus = 7 ;
   Bus = 46 ;
   Bus = 44 ;
   No
   
   
   
   
   
   
   
   
   3 ?- busServes(174,downtown).
   Yes
   
   4 ?- busConnects(wallingford,ballard,Bus).
   Bus = 46 ;
   Bus = 44 ;
   No
   
   5 ?- busConnects(eastlake,seaTacAirport,Bus).
   No
   
   6 ?- busConnectsVia(eastlake,seaTacAirport,TransferLoc,Bus1,Bus2).
   TransferLoc = downtown
   Bus1 = 25
   Bus2 = 174 ;
   No
   

   Copy and paste these relations into your Prolog file:

/* busServes(LineNo,Location) if Metro Bus No. LineNo serves, i.e. has
 * a stop in, area Location
 *
 * source:  http://transit.metrokc.gov/bus/area_maps/seattle.html
 */

busServes(7,universityDistrict).
busServes(7,capitolHill).
busServes(7,broadway).
busServes(7,downtown).
busServes(7,internationalDistrict).
busServes(7,rainierValley).
busServes(7,columbiaCity).
busServes(7,rainierBeach).

busServes(25,downtown).
busServes(25,eastlake).
busServes(25,montlake).
busServes(25,universityVillage).
busServes(25,childrensHospital).
busServes(25,laurelhurst).

busServes(46,governmentLocks).
busServes(46,ballard).
busServes(46,fremont).
busServes(46,wallingford).
busServes(46,universityDistrict).

busServes(44,governmentLocks).
busServes(44,ballard).
busServes(44,wallingford).
busServes(44,universityDistrict).
busServes(44,uwCampus).
busServes(44,montlake).

busServes(174,downtown).
busServes(174,sodo).
busServes(174,duwamish).
busServes(174,seaTacAirport).
busServes(174,midway).
busServes(174,federalWay).

busServes(34,tukwila).
busServes(34,duwamish).
busServes(34,gatewayCorporateCenter).
busServes(34,whiteCenter).
busServes(34,fauntleroy).
busServes(34,westSeattleJunction).
busServes(34,admiralDistrict).