1:- module(interval, [interval/2, interval/3, op(150, xfx, ...)]).    2
    3:- multifile int_hook/4.    4:- multifile eval_hook/2.    5:- multifile mono/2.    6:- multifile interval_/3.    7:- multifile instantiate/2.    8:- multifile interval_hook/3.    9
   10:- set_prolog_flag(float_overflow, infinity).   11:- set_prolog_flag(float_undefined, nan).   12:- set_prolog_flag(float_zero_div, infinity).   13
   14:- nb_setval(digits, 2).   15
   16:- consult(['../inst/prolog/lib/interface', '../inst/prolog/lib/core', '../inst/prolog/lib/op']).

This module adds interval arithemtic to Prolog. An interval is represented as L...U, where L stands for the lower bound and U for the upper bound. If the upper bound is a negative number, it has to be written with an additional space, e.g., -3... -2, or in the infix notation, ...(-3, -2). The interval/2 parses and evaluates the arithemtic expression with such intervals to a result.

 interval(+A, ?Res)

Evalutes an expression to an interval. If the first argument is already an interval, no evaluation is performed. Supported operations:

• Basic arithemtic: addition '+', subtraction '-', division '/', multiplication '*'
• Square root for positive interval: 'interval(sqrt(X), Res)'
• Square root for negative or mixed interval: 'interval(sqrt1(X), Res)'
• Power: 'interval(X^atomic(N), Res)' with N being a natural number
• Absolute value: 'interval(abs(X), Res)'
• Comparison: '>', '<', '>=', '=<', '=\=', '=:='
• Rounding: 'interval(round(1.356...1.634, atomic(2)), Res)'

Arguments:

A	- is the expression to be evaluted.
Res	- is the result.