prolog - university of calgary in...

02/23/2010 CPSC 449

Computer Science

Unless otherwise noted, all artwork and illustrations by either Rob Kremer or Jörg Denzinger (course instructors)

PrologStructuring Programs

306

2015/01/05 CPSC 449

Structuring programs

■While in theory the rules (clauses) with a particular predicate as head can be distributed over several files that are consulted by the interpreter to load everything required by a program, naturally the sequence in which these rules end up in the data base will have a big impact on the program ■Therefore it is a good practice to cluster the rules

with a particular head in one file and also within this file • GNU Prolog forces clustering of rules (except if you use

the directives discontiguous/1 or multifile/1)

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2015/01/05 CPSC 449

PROLOG program structure

■There really is not much of a structure required in PROLOG programs, most of the structure we see in books or real programs is voluntary by the programmer ■ In most PROLOG versions there are

-No modules -No types and type declarations -No particular layout

■The only real conventions are that every rule ends with a ".", that atoms are separated by "," and that ";" indicates an "or" in the body of a rule

308

02/23/2010 CPSC 449

Computer Science

Unless otherwise noted, all artwork and illustrations by either Rob Kremer or Jörg Denzinger (course instructors)

PrologExecuting Programs

309

2015/01/05 CPSC 449

Executing programs

■PROLOG is usually an interpreted language, although there are compilers that compile in bytecode for the Warren Abstract Machine (Java got the idea of the Java Virtual Machine from there)

■GNU Prolog is compiled for WAM.

■A PROLOG program is usually loaded into the interpreter's data base using the consult/1 predicate ■consult/1 expects as argument a file name and the

exact format depends on the machine the interpreter runs on (on our machines you need consult('myfile').)

310 2015/01/05 CPSC 449

Executing programs

■GNU Prolog can be “scripted” by adding the line:
#!/opt/local/bin/gprolog —consult-file
as the first line of the Prolog file. • “#” is treated as a comment if it’s the first line of a file. • UNIX interprets the file with the “shebang” protocol.

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