View source for Programmer Guide/Command Reference/EVAL Intro/EVAL

{{DISPLAYTITLE:{{SUBPAGENAME}}}}
==EVAL==

The <code>EVAL</code> command can be used to evaluate numerical expressions. These expressions can be constants, scalar variables, vectors, matrices or <code>[[Programmer Guide/Command Reference/EVAL/EVAL Subcommands|EVAL]]</code>[[Programmer Guide/Command Reference/EVAL/EVAL Subcommands| subcommands]].

<pre>
// 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.
</pre>
Syntax

An <code>EVAL</code> command uses the following general syntax:

<code>result := eval expression</code>

<code>result := evalcheck expression</code>

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

<code>result := eval (5 * 10) % 3</code>

or a subcommand, e.g.

<code>result := eval init(10,1,1)</code>

or a combination thereof:

<code>result := eval 5+max(fill(6,1,1))</code>

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

Numerical and Logical Operators

The <code>EVAL</code> command supports the following numerical operators:

{|
|-
|<code>></code>
|less than
|-
|<code><</code>
|greater than
|-
|<code><=</code>
|less than or equal to
|-
|<code>>=</code>
|greater than or equal to
|-
|<code>==</code>
|equal to
|-
|<code>!=</code>
|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 <code>EVAL</code> command also supports the following logical operators:

{|
|-
|<code>||</code>
|logical or
|-
|<code>&&</code>
|logical and
|-
|<code>!</code>
|unary not
|}

A C<nowiki>-</nowiki>like '<code>? :'</code> operator is also supported:

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

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

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

Examples

See the script <code>eval_examples.sts</code> for an extensive list of examples.

Command History

The <code>EVAL</code> command was added to the S_TOOLS-STx language in version 3.7.0. The <code>EVAL</code> command replaces and extends the <code>EVALUATE</code> command. If the <code>EVAL</code> 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 [[Programmer Guide/Command Reference/EVAL/Numerical objects|numerical objects]] than just the scalars <code>INT</code> and <code>NUM</code>.

{|
|-
|
|}