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How to write a Prolog program

This chapter delves into the essentials of writing Prolog programs by guiding you through designing data structures, developing algorithms using selection and recursion, and translating those algorithms into Prolog code. You will learn how to verify the correctness of your programs through bottom-up testing and how to enhance your code with appropriate comments. Additionally, the chapter includes practical examples such as creating a partition function and implementing sorting methods to solidify your understanding of declarative specifications, skeletons, and bodies of predicates.

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How to write a Prolog program

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  1. Simply Logical – Chapter 3 How to write a Prolog program

  2. Simply Logical – Chapter 3 • Design data structures to represent input, output and intermediary data as required • Design algorithms to perform the task using only 2 forms of control: selection and recursion. The algorithm is developed ina hierarchicaltop-down mannerand terminates when all subtasks are elementary. • Translate the algorithms form the step 2 into Prolog programs. • Check correctness of programs by checking correctness of each procedure (testing is carried out bottom-up). • Add comments specifying a typical query to the program.

  3. Simply Logical – Chapter 3 p.74-6 • Write down declarative specification of partition • % partition(L,N,Littles,Bigs) <- Littles contains numbers • % in L smaller than N, • % Bigs contains the rest • Identify recursion and ‘output’ arguments • Write down skeleton • partition([],N,[],[]). • partition([Head|Tail],N,?Littles,?Bigs):-/* do something with Head */partition(Tail,N,Littles,Bigs). Logic programming methodology

  4. Simply Logical – Chapter 3 p.74-6 • Complete bodies • partition([],N,[],[]). • partition([Head|Tail],N,?Littles,?Bigs):-Head < N,partition(Tail,N,Littles,Bigs),?Littles = [Head|Littles],?Bigs = Bigs. • partition([Head|Tail],N,?Littles,?Bigs):-Head >= N,partition(Tail,N,Littles,Bigs),?Littles = Littles,?Bigs = [Head|Bigs]. • Fill in ‘output’ arguments • partition([],N,[],[]). • partition([Head|Tail],N,[Head|Littles],Bigs):-Head < N,partition(Tail,N,Littles,Bigs). • partition([Head|Tail],N,Littles,[Head|Bigs]):-Head >= N,partition(Tail,N,Littles,Bigs). Methodology

  5. Simply Logical – Chapter 3 p.76 • Write down declarative specification for sorting • % sort(L,S) <- S is a sorted permutation of list L • Write down skeleton • sort([],[]). • sort([Head|Tail],?Sorted):-/* do something with Head */sort(Tail,Sorted). • Complete body (auxiliary predicate needed) • sort([],[]). • sort([Head|Tail],WholeSorted):-sort(Tail,Sorted),insert(Head,Sorted,WholeSorted). Writing a sort predicate

  6. Simply Logical – Chapter 3 p.77 • Write down declarative specification • % insert(X,In,Out) <- In is a sorted list,e.g.[2,4,7,9] • % Out is In with X inserted in the proper place • % ?- insert(5,[2,4,7,9],Out). Out=[2,4,5,7,9] • Write down skeleton • insert(X,[],?Inserted). • insert(X,[Head|Tail],?Inserted):-/* do something with Head */insert(X,Tail,Inserted). Writing an insert predicate

  7. Simply Logical – Chapter 3 p.77 • Complete bodies • insert(X,[],?Inserted):-?Inserted=[X]. • insert(X,[Head|Tail],?Inserted):-X > Head,insert(X,Tail,Inserted),?Inserted = [Head|Inserted]. • insert(X,[Head|Tail],?Inserted):-X =< Head,?Inserted = [X,Head|Tail]. • Fill in ‘output’ arguments • insert(X,[],[X]). • insert(X,[Head|Tail],[X,Head|Tail]):-X =< Head. • insert(X,[Head|Tail],[Head|Inserted]):-X > Head,insert(X,Tail,Inserted). Writing an insert predicate

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