Jalog Quick Reference

Built-in Predicates

assertz(Fact)

Stores the fact Fact to the end of the database.

Example:

assertz(connection(7588, 9032))

bound(Var)

Succeeds, if the parameter Var is bound, otherwise fails.

comline_arg(Number, Option, Argument)

    Not implemented like other built-in predicates. Instead, each command line argument is stored to the database as a separate fact.

Returns information about one command line argument, if one can be found.

A command line example:

> java -jar jalog.jar myprogram.pro -foo=bar -up report.txt

    Note the equal sign separating an option and its argument.

Parameters of this command line are stored to the database prior to starting myprogram.pro as following facts:

comline_arg(1, "foo", "bar").
comline_arg(2, "up", "").
comline_arg(3, "", "report.txt").

consult(Filename)

Reads the facts and rules to the database and executes the goals from the file Filename.

Example:

consult("route_data.pro")

dynamic(PredicateIndicator)

Prevents an error message, if no clause matching PredicateIndicator is found in the database. This is intended for predicates that can be asserted and retracted in runtime. This is intended to be used as a directive.

A PredicateIndicator must be a string of form Functor/Arity .

Example:

:- dynamic("route/3").

exit

Terminates the program with exit code 0.

However, if exit is called (typically very indirectly) in execution of the first argument of trap then control is transferred to the trap predicate.

exit(Int_value)

Terminates the program with exit code Int_value.

However, if exit is called (typically very indirectly) in execution of the first argument of trap then control is transferred to the trap predicate.

fail

This call fails always.

foreach_(Var, List )

Binds the first variable Var in the first call to the first item of the list List in the second variable, and in recalls to the succeeding items.

foreach_(X, [1, 2, 3]), write(' ', X), fail. prints 1 2 3

is_char(Var)

Succeeds, if the parameter Var is bound to a character value.

is_compound(Var)

Succeeds, if the parameter Var is bound to a compound structure.

is_integer(Var)

Succeeds, if the parameter Var is bound to an integer value.

is_list(Var)

Succeeds, if the parameter Var is bound to a list structure.

is_real(Var)

Succeeds, if the parameter Var is bound to a real value.

is_string(Var)

Succeeds, if the parameter Var is bound to a string value.

nl

Prints a newline character.

not(Predicate_call)

Fails, if Predicate_call succeeds, succeeds, if Predicate_call fails.

Example:

not(connection(7588, 9032)) fails, if connection(7588, 9032) is found from the database, otherwise succeeds.

trap(Predicate_call, Var_exit, Exception_handler)

Executes Predicate_call. If an exception happens or exit is called within the call, the exit code is bound to Var_exit, Exception_handler is called, and finally the whole trap predicate fails.

Example:

trap(analyze(Situation, Results), X, write("*** Exception ", X, '!'))
        

write(parameters)

Prints the values of the parameters without punctuation or whitespace in between.

write('a', "bc", 3.142) prints abc3.142

writeln(parameters)

As write but followed by nl

writeq(parameters)

Prints the values of the parameters in lexical notation so that they can be read back. Strings are enclosed in double quotes and characters are enclosed in single quotes.

writeq('a', "bc", 3.142) prints 'a'"bc"3.142

writeq(a('b', 'c')) prints a('b','c')

Arithmetic Expressions

Operators

Operator Precedence

Arithmetic operators have their normal precedences. Expressions in parenthesis () are evaluated first. Operators multiplication, division, mod, and div have the same precedence and are evaluated from left to right.

Operators and Data Types