# Custom Parsers

A very powerful feature of the Porting Project is the built-in interpreter that is used to support *SalCompileAndEvaluate* and to resolve bind/into expressions in sql statements. The interpreter executes a code tree expressed as a structured collection of code objects. The code tree can be generated in any way. Usually it's generated by a parser that parses the source code language into a code tree.

The built-in parser supports C# syntax only. However it is possible to plug-in a custom parser that is responsible only for the parsing of the source code. A custom parser class needs only to implement the *PPJ.Runtime.Scripting.IScriptParser* interface which defines only one method:

```csharp
public interface IScriptParser
{
 ASTNode Parse(string script);
}
```

The custom parser should only parse the source code text into an Abstract Statement Tree (AST).

To register the custom parser to be used only with SalCompileAndEvaluate use:

```csharp
Sal.Interpreter.Parser = new MyParser();
```

To register the custom parser to be used only with XSalScript, use:

```csharp
XSalScript.Interpreter.Parser = new MyParser();
```

To register the custom parser to be the default parser for everything, including bind/into expressions evaluations, use:

```csharp
PPJ.Runtime.Scriping.ScriptEngine.DefaultParserType = typeof(MyParser);
```

All AST classes are derived from *ASTNode* and are available in the *PPJ.Runtime.Scripting* namespace. There is no public reference manual about the *AST* classes and if you need to write your parser we can provide sample code for your reference and professional support upon request.


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