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) modulo Y |
| X xor Y | X exclusive or Y |
| X * Y | multiplication |
| X + Y | addition |
| X-Y | subtraction |
| X/Y | division |
| X//Y | integer division |
| X/\Y | integer bitwise conjunction |
| X « Y | integer bitwise left of X by Y places |
| X » Y | integer bitwise right shift of X by Y places |
| X\/Y | integer bitwise disjunction |
| X^Y | X to the power Y |
| \X not(X) | integer bitwise negation |
| 0 ‘ Char | the ASCII code of Char |
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 exponential function |
| 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 logarithm |
| log10(X) | base 10 logarithm |
| random | returns a random floating point number such that 0.0 ≤ X < 1.0 |
| realtime | actual time in seconds since ALS Prolog started |
| 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.
NOTES
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.