Compile

Parses an expression string and returns it as a compiled ITbExpression.

Syntax: service.Compile( expression )

service
required An object expression that evaluates to a TbExpressionService object.
expression
required A String containing a twinBASIC-syntax expression — for example, "Sqr(2) + 1" or "UCase(FirstName) & "" "" & UCase(LastName)".

The return value is an ITbExpression. Calling Evaluate on it runs the expression and produces the current value; the same instance can be evaluated as many times as needed.

Symbols referenced in expression — function names, object members, properties — are resolved against the binders registered with service at the time of the call. At least one binder must be registered before Compile is called; the most common starting point is AddStdLibraryBinder, which exposes the standard runtime library.

Compilation is the relatively expensive step; evaluation reuses the compiled form. When a piece of source text is going to drive repeated evaluation — a formula column refreshed every row, a watch expression sampled in a debugger — compile it once and keep the ITbExpression around.

If expression is malformed, or references a symbol that no registered binder can resolve, Compile raises a run-time error.

Example 

Dim Service As TbExpressionService = New TbExpressionService
Service.AddStdLibraryBinder()

Dim Square As ITbExpression = Service.Compile("Sqr(2)")
Debug.Print Square.Evaluate()    ' 1.4142135623731
Debug.Print Square.Evaluate()    ' Same compiled instance, evaluated again.

See Also