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LING 388: Language and Computers

LING 388: Language and Computers. Sandiway Fong Lecture 6: 9/7. Administrivia. Homework 2 out today usual rules due next Thursday by midnight. Building and Taking Atoms Apart built-in predicate atom_chars/2 has two modes of usage atom_chars( symbol , list ) takes names apart

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LING 388: Language and Computers

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  1. LING 388: Language and Computers Sandiway Fong Lecture 6: 9/7

  2. Administrivia • Homework 2 • out today • usual rules • due next Thursday by midnight

  3. Building and Taking Atoms Apart built-in predicate atom_chars/2 has two modes of usage atom_chars(symbol,list) takes names apart ?- atom_chars(will,X). X=[w,i,l,l] builds names from a list of characters ?- atom_chars(X,[’J’,o,h,n]). X=‘John’ Building and Taking Lists Apart append/3 is a built-in predicate in SWI-Prolog defined as follows: append(L1,L2,L3) is true if list L3 is the linear concatenation of lists L1 and L2 concatenate two lists together ?- append([1],[2,3],X). X = [1,2,3] split a list up into two parts ?- append(X,Y,[1,2]). X=[] Y=[1,2] X=[1] Y=[2] X=[1,2] Y=[] Last Time

  4. Recursive Definition Base Case Recursive Case [member/2 is already taken in SWI-Prolog, let’s us mem/2.] Let’s define mem/2 such that ?- mem(List,X). is true if X is a member of List Examples: ?- mem([1,2,3],2). true ?- mem([1,2,3],4). false Exercise 1

  5. Let’s define mem/2 such that ?- mem(List,X). is true if X is a member of List Examples: ?- mem([1,2,3],2). true ?- mem([1,2,3],4). false Recursive Definition Base Case mem([X|_],X). X is a member of a list is X is the head of that list (tail = _ ) Recursive Case mem([_|L],X):- mem(L,X). X is a member of a list [_|L] if X is a member of its tail L Exercise 1

  6. Put the definition of mem/2 in a file and load it into Prolog: mem([X|_],X). mem([_|L],X):- mem(L,X). test to see if it’s loaded properly using ?- listing. Run the following queries: ?- mem([1,2,3],2). ?- mem([],2). ?- mem([1,2,3],X). what answer(s) does this last query give? Exercise 1

  7. (6pts) Give the complete (i.e. all answers) step-by-step computation tree for ?- mem([1,2,3],X). given the database mem([X|_],X). mem([_|L],X):- mem(L,X). Hint: using ?- trace. will help but you will need to list out the matches and variable binding at each step see Lecture 5 slides for app/3 to see what format you should use Homework Question 1

  8. Modal auxiliary verbs in English generally have contracted negative counterparts should shouldn’t would wouldn’t could couldn’t may *mayn’t [* indicates ungrammaticality] Let’s write a rule to form the contracted negated form call the predicate addNT/2 ?- addNT(Word,WordNT). Word = symbol WordNT = symbol with n’t suffixed Examples: ?- addNT(should,X). X = ’shouldn\’t’ Exercise 2

  9. We can use atom_chars/2 atom_chars(symbol,list) takes names apart ?- atom_chars(will,X). X=[w,i,l,l] builds names from a list of characters ?- atom_chars(X,[’J’,o,h,n]). X=‘John’ Definition (rule): addNT(W,Wnt) :- atom_chars(W,L), append(L,[n,’\’’,t],Lnt), atom_chars(Wnt,Lnt). add this rule to the database ?- listing. addNT(A, C) :- atom_chars(A, B), append(B, [n, '\'', t], D), atom_chars(C, D). run queries ?- addNT(should,X). ?- addNT(would,X). ?- addNT(john,X). Exercise 2

  10. Assume database includes facts: modal(should). “should is a modal” modal(would). “would is a modal” modal(could). “could is a modal” modal(may). “may is a modal” (4pts) Modify the definition of addNT/2 to accept only modals Demonstrate your program works correctly for: ?- addNT(should,X). ?- addNT(would,X). ?- addNT(john,X). Submit both your program and queries as your answer put everything together, not in separate files! Homework Question 2

  11. (4pts) Further modify your definition of addNT/2 to exclude the ungrammatical case: i.e. ?- addNT(may,X). No should shouldn’t would wouldn’t could couldn’t may *mayn’t Homework Question 2

  12. (6pts) Extra Credit Question Notice that the following query doesn’t work: ?- addNT(X,'shouldn\'t'). ERROR: atom_chars/2: Arguments are not sufficiently instantiated Write the corresponding “subtract n’t” rule, call it subNT/2, for removing the n’t suffix: ?- addNT(X,'shouldn\'t'). X = should Homework Question 2

  13. Let’s define a recursive predicate for reversing lists Examples: [1,2] [2,1] [1,2,3] [3,2,1] [1] [1] [] [] Definition reverse([],[]). reverse([X|L],R) :- reverse(L,LR), append(LR,[X],R). Exercise 3 • Run queries ?- reverse([1,2,3],X). ?- reverse(X,[1,2,3]). what happens when you ask for more answers?

  14. (6pts) Define a predicate pallindrome/1 that is true when a word can be spelt the same forwards or backwards Examples: radar redivider abba Demonstrate your program works on queries like: ?- pallindrome(radar). Yes ?- pallindrome(dog). No Homework Question 3 Hint: use atom_chars and reverse

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