Expose formula parser

[Felx-B]

Hi,
I'd like to parse the formula before executing it :

Use case:

• In a grid with available columns A, B, C, D, user choose to display A, B
• Application execute SQL query to populate grid:
  SELECT A, B FROM MyTable
• Now we want to let user create custom columns, powered by PowerFx
• User defines column F = ThisItem.C & ThisItem.D
• User chooses to display A, B, F

Here we need to parse formula F to know we need to query C, D from DB
=> SELECT A, B, C, D FROM MyTable

Is there any way to achieve this ?
Could we expose the formula parser to retrieve used fields ?

Thank you

[MikeStall]

You can parse the expression and get the top-level identifiers,

Power-Fx/src/libraries/Microsoft.PowerFx.Interpreter/RecalcEngine.cs

Line 175 in 12b87ac

result.TopLevelIdentifiers = DependencyFinder.FindDependencies(binding.Top, binding);

This quickly gets challenging as the expression gets more complicated.
In your example above, Check() would show you the reference to ThisItem, but it looks like you're trying to see which fields on ThisItem are being referenced?

We do want to expose syntax tree and bindings, but they're still internal.

[Felx-B]

You guessed right, I need the fields used in ThisItem, so the Check() method won't help me.
I'm please to hear you have plan to expose the syntax tree, so for now I think I'll go with a simple regex, until I get more robust way.

Thank you for the reply

[MikeStall]

FYI parser is now exposed in public surface area.