Execute a user-defined function (from Functions list of this program).
Looks for given FunctionName.
IgnoreMissingFunction says what to do in case of missing function: if true, it will be simply ignored (ExecuteFunction will silently do nothng). If false (default) then we will raise exception ECasScriptMissingFunction.
Sets function parameters to given values (number of parameters must match, otherwise ECasScriptError). Values from your parameters are set as our parameters TCasScriptParameterValue.SourceValue, so script can read and write your values.
Environment (outside information) for this program.
This will be created and is owned by this TCasScriptProgram instance. You should take care to copy this reference to all expressions within this program (for example ParseProgram does this), this way all expressions share the same Environment instance.