Runtime expression evaluation in ActionScript

Finally I have a bit of free time to write down this post. Some days ago a guy on the forum asked about how to Dissertation Proposals On Corporate Governance evaluate at runtime simple mathematical expressions with support for symbols and function calls.

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Now that the eval function have been removed from the language for reasons I’ve not enought time to talk about, we need to parse and execute those expressions manually.

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I built a simple Actionscript library that can be used to parse mathematical expressions: it has support for function calls, for variables and it is able to convert the expression into a postfix rappresentation if you may need it. The expression parser is quite simple and have been built manually following some concepts related to programming language compilers; it includes a Scanner (or lexer – however you want to call it) to tokenize the expression, a Parser that convert the expression into an Abstract Syntax Tree and a simple routine that evaluates that AST using a Symbol Table as evaluation context.

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Viagra For Sale Canada Pharmacy There are no comments inside the code right now; I hope to find a little bit of time to write an in depth discussion about this topic. In the mean time you can continue reading the entry for a general explanation about how does the code works and for some examples that may be useful.

Here is a simple example that shows how does the code works:

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import it.sephiroth.expr.CompiledExpression;
import it.sephiroth.expr.Parser;
import it.sephiroth.expr.Scanner;
public class Example
{
public static function run(): void
{
var expression: String = "sin( x / ( 8 / 2 + (-0.12 + 2.3) * x / x ) ) * 100";
var scanner: Scanner = new Scanner( expression );
var parser: Parser = new Parser( scanner );
var compiled: CompiledExpression = parser.parse();
var context: Object = {
x:    100,
sin:   Math.sin,
cos:  Math.cos
};
trace( 'Postfix:', compiled.toString() );
trace( 'Result:', compiled.execute( context ) );
}
}

Best Dissertation Writers London Before I forgot, you can download the source code here with a simple example included.

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