is/2

Module: builtins

is/2 — evaluates an arithmetic expression

FORMS

Result is Expression

DESCRIPTION

Expression should be a ground term that can be evaluated. Numbers evaluate as themselves, and a list evaluates as the first element of the list. The operators listed in Arithmetic Operators and Arithmetic Functions can also be evaluated when their arguments can be evaluated. If Result is an unbound variable, then it will be bound to the numeric value of Expression. If Result is not unbound, then it will be evaluated, and the value of the Result will be unified with the value of Expression.

Arithmetic Operators

Operator Description
-X unary minus
X div Y integer division
X mod Y X(integer)
X xor Y X
X * Y multiplication
X + Y addition
X-Y subtraction
X/Y division
X//Y integer division
X/\Y integer bitwise
X < < Y integer bitwise left
X > > Y integer bitwise right shift of X by Y places
X\/Y integer bitwise
X^Y X to the
\X not(X) integer bitwise
0 ‘ Char the

Arithmetic Functions

Function Description
abs(X) absolute value
acos(X) arc cosine
asin(X) arc sine
atan(X) arc tangent
cos(X) cosine
cputime CPU time in seconds since ALS Prolog started.
exp(X) natural
exp10(X) base 10 exponential function
floor(X) the largest integer not greater than X
heapused heap space in use, in bytes
j0(X) Bessel function of order 0
j1(X) Bessel function of order 1
log(X) natural
log10(X) base 10 logarithm
random returns a
realtime actual
round(X) integer rounding of X
sin(X) sine
sqrt(X) square root
tan(X) tangent
trunc(X) the largest integer not greater than X
y0(X) Bessel function of second kind of order 0
y1(X) Bessel function of second kind of order 1

EXAMPLES

?- 2 is 3-1.

yes.

?- X is 6*7

X=42

yes.

?- X is 2.5+3.5.

X=6

yes.

?- Result is sqrt(2).

Result=1.414213562

yes.

ERRORS

is/2 fails when it attempts to evaluate an unknown operator, or if Expression is not ground. Failure also occurs if there are any arithmetic faults, such as overflow, underflow, or division by zero.

ALS Prolog complies to the ISO Prolog Standard regarding errors. A calculation error will be thrown on overflow, underflow, division by zero, or use of an unrecognized arithmetic operator.