1 / 9

Side effects in Prolog

Side effects in Prolog. Lecturer: Xinming (Simon) Ou CIS 505: Programming Languages Fall 2010 Kansas State University. Side effect. When using Prolog as a programming language, it is often needed to create side effects e.g. printing to the display, writing to files

purity
Download Presentation

Side effects in Prolog

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Side effects in Prolog Lecturer: Xinming (Simon) Ou CIS 505: Programming Languages Fall 2010 Kansas State University

  2. Side effect • When using Prolog as a programming language, it is often needed to create side effects • e.g. printing to the display, writing to files • Some side effect will influence the Prolog execution environment and execution behaviors

  3. Asserting facts • Facts can be loaded into the Prolog database. • e.g. ?- load_dyn(‘input.P’). • The predicates defined in input.P are called “dynamic predicates”. • They can be added to the database using the load_dyn command, or the “assert” command • e.g. ?- assert(parent(bill, mary)). • They can be removed from the database using the “retract”, or “retractall” command. • E.g. ?- retract(parent(X,Y)). ?- retractall(parent(X,Y)).

  4. Printing statements • Print a term • e.g. write(‘Hello world’). write(world). write(X). • Print a new line • nl. • writeln(‘abc’). • write(‘\n’).

  5. Cut • The cut command “!” will eliminate all the choice points for the parent goal. • e.g. member(A, [A|_As]) :- !. member(A, [_B|Bs]) :- member(A, Bs). • But this will break the declarative semantics. Try this: ? – member(A, [1,2,3]).

  6. Negation in Prolog • Negation by failure: • not L succeeds if L fails. • It is equivalent to: not(L) :- L, !, fail. not(L). • Negation by failure is not logical negation, when the literal contains variables when the negation is called.

  7. Assignment 7 • Use Prolog to implement the interpreter in assignment 2. • memory and environment implemented using dynamic predicates • env(Name, Type, Location).

  8. Memory • The memory is a mapping from locations to values. The memory/2 predicate provides the mapping. • memory(Location, Value). • memoryCounter(Length) returns the number of cells in the memory. • memoryAppend(Value) add a new memory cell and put Value into it. • memoryUpdate(Location, Value) updates the memory location with the value.

  9. Environment • Provides mapping from a variable name to its type and memory location that holds the value. • env(name, type, value) provides the mapping type is either [‘int’] or [‘ptr’, ‘int’]

More Related