ExpressionProcessor (NanoDB SQL Relational Database 0.1-SNAPSHOT API)

All Known Implementing Classes:

Expression.SymbolFinder, SubquerySchemaComputer
```
public interface ExpressionProcessor
```
This interface is used to implement scans or transformations of expression trees by specifying what to do when entering or leaving each expression node. When leaving an expression node, a replacement expression may be returned that will replace the expression node that was just left.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`enter(Expression node)`	This method is called when expression-traversal is entering a particular node in the expression tree.
`Expression`	`leave(Expression node)`	This method is called when expression-traversal is leaving a particular node in the expression tree.

- Method Detail
  - enter
```
void enter(Expression node)
```
    This method is called when expression-traversal is entering a particular node in the expression tree. It is not possible to replace a node when entering it, because this would unnecessarily complicate the semantics of expression-tree traversal.
    
    Parameters:
    
    node - the Expression node being entered
  - leave
```
Expression leave(Expression node)
```
    This method is called when expression-traversal is leaving a particular node in the expression tree. To facilitate mutation of expression trees, this method must return an Expression object: If the expression processor wants to replace the node being left with a different node, this method can return the replacement node; otherwise, the method should return the passed-in node.
    
    Parameters:
    
    node - the Expression node being left
    
    Returns:
    
    the Expression object to use for the node being left; either node if no changes are to be made, or a new Expression object if node should be replaced.