Programmer Guide/Command Reference/EVAL Intro/EVAL

EVAL

The EVAL command can be used to evaluate numerical expressions. These expressions can be constants, scalar variables, vectors, matrices or EVAL subcommands.

// if the variable #v does not exist then the following command
// assigns a table item to #v.
$#v := eval vv(1,2,3,4)
// if #v is a value item, then #v remains a value item.

Syntax

An EVAL command uses the following general syntax:

result := eval expression

result := evalcheck expression

An expression can be either a numerical expression, e.g.

result := eval (5 * 10) % 3

or a subcommand, e.g.

result := eval init(10,1,1)

or a combination thereof:

result := eval 5+max(fill(6,1,1))

If the expression is syntactically ill-formed, an error (EVAL) or warning (EVALCHECK) is reported. See the example script expression_check.sts for details.

Numerical and Logical Operators

The EVAL command supports the following numerical operators:

>	less than
<	greater than
<=	less than or equal to
>=	greater than or equal to
==	equal to
!=	not equal to

Note that two numbers/vectors/matrices are considered equal if (and only if)

(a) their dimensions are the same; and (b) all elements are numerically equal.

The EVAL command also supports the following logical operators:

		logical or
&&	logical and
!	unary not

A C-like '? :' operator is also supported:

result := eval 1 < 2 ? 1+2 : 1-2 // result is 3

Note that unlike C, nested uses of this operator must be surrounded by brackets, e.g.:

result := eval 1 > 2 ? (5 == 5 ? 5 : 0) : (4 == 5 ? 3 : 4) // returns 4

Examples

See the script eval_examples.sts for an extensive list of examples.

Command History

The EVAL command was added to the S_TOOLS-STx language in version 3.7.0. The EVAL command replaces and extends the EVALUATE command. If the EVAL command is not assigning to an existing item, a table is assigned. Note that the current maximum number of arguments is 64 (S_TOOLS-STx version 3.8.0). As of version 3.7.0, S_TOOLS-STx has more numerical objects than just the scalars INT and NUM.