Power Fx in desktop flows

Power Fx is the low-code language for expressing logic across Microsoft Power Platform. It's a general-purpose, strong-typed, declarative, and functional programming language.

Power Fx is expressed in human-friendly text. It's a low-code language that makers can work with directly in an Excel-like formula bar or Visual Studio Code text window. The "low" in low-code is due to the concise and simple nature of the language, making common programming tasks easy for both makers and developers.

Power Fx enables the full spectrum of development from no-code makers without any programming knowledge to pro-code for the professional developers. It enables diverse teams to collaborate and save time and efforts.

Using Power Fx in desktop flow

To use Power Fx as an expression language in a desktop flow, you have to create a desktop flow and enable the respective toggle button when creating the flow through Power Automate for desktop's console.

Differences in Power Fx enabled flows

If you're transitioning from flows where Power Fx is disabled, you might notice some differences. To streamline your experience while creating new desktop flows, here are some key concepts to keep in mind:

• In the same fashion as Excel formulas, desktop flows that use Power Fx as their expression language use 1 (one) based array indexing instead of 0 (zero) based indexing. For example, expression =Index(numbersArray, 1) returns the first element of the numbersArray array.

• Variable names are case-sensitive in desktop flows with Power Fx. For example, NewVar is different than newVar.

• When Power Fx is enabled in a desktop flow, variable initialization is required before use. Attempting to use an uninitialized variable in Power Fx expressions results in an error.

• The If action accepts a single conditional expression. Previously, it accepted multiple operands.

• While flows without Power Fx enabled have the term "General value" to denote an unknown object type, Power Fx revolves around a strict type system. In Power Fx enabled flows, there's a distinction between dynamic variables (variables whose type or value can be changed during runtime) and dynamic values (values whose type or schema is determined at runtime). To better understand this distinction, consider the following example. The dynamicVariable changes its type during runtime from a Numeric to a Boolean value, while dynamicValue is determined during runtime to be an untyped object, with its actual type being a Custom object:

  

• Values that are treated as dynamic values are:

  • Data tables
  • Custom objects with unknown schema
  • Dynamic action outputs (for example, the "Run .NET Script" action)
  • Outputs from the "Run desktop flow" action
  • Any action output without a predefined schema (for example, "Read from Excel worksheet" or "Create New List")

• Dynamic values are treated similarly to the Power Fx Untyped Object and normally require explicit functions to be converted into the required type (for example, Bool() and Text()). In order to streamline your experience, there's an implicit conversion when using a dynamic value as an action input or as a part of a Power Fx expression. There's no validation during authoring, but depending on the actual value during runtime, a runtime error occurs if the conversion fails.

• Whenever a dynamic variable is used, a warning message stating "Deferred type provided" is presented. These warnings arise due to Power Fx's strict requirement for strong-typed schemas (strictly defined types). Dynamic variables aren't permitted in lists, tables, or as a property for Record values.

• By combining Run Power Fx expression action with expressions using Collect, Clear, ClearCollect, and Patch functions you can emulate behavior found in the actions Add item to list and Insert row into data table which were previously not available for Power Fx enabled desktop flows. While both actions are still available, use the Collect function when working with strongly typed lists (for example, a list of files). This function ensures the list remains typed, as using the Add Item to List action converts the list into an untyped object.

Examples

• The =1 in an input field is equivalent to the numeric value 1.
• The = variableName is equal to the variableName variable's value. 
• The expression = {'prop':"value"} returns a record value that is equivalent to a custom object.
• The expression = Table({'prop':"value"}) returns a Power Fx table that is equivalent to a list of custom objects. 
• The expression - = [1,2,3,4] creates a list of numeric values.
• To access the value from a List, use the function Index(var, number), where var is the name of the List and number is the position of the value to be retrieved.
• To access a data table cell using a column index, use the Index() function. =Index(Index(DataTableVar, 1), 2) retrieves the value from the cell in row 1 within column 2. =Index(DataRowVar, 1) retrieves the value from the cell in row 1.
• To include an interpolated value in an input or a UI/web element selector, use the following syntax: Text before ${variable / expression} text after
  • Example: The total number is ${Sum(10, 20)}

Available Power Fx functions

For the complete list of all available functions in Power Automate for desktop flows, go to Formula reference - desktop flows.

Known issues and limitations

• The following actions from the standard library of automation actions aren't currently supported:
  • Switch
  • Case
  • Default case
• Some Power Fx functions presented through IntelliSense aren't currently supported in desktop flows. Those functions display the following design time error when used: "Parameter 'Value': PowerFx type 'OptionSetValueType' isn't supported."

What's new

This section lists what changed in each update.

2.48

In September 2024 release:

• Re-enable previously unsupported list and data table manipulation actions from the Variables category.
• Native untyped object support, for custom objects, lists, and data tables. Learn more about untyped objects at Untyped object data type.
  • This change was introduced to reduce the design-time warnings and usage of deferred types. Untyped object is a way to handle types with unknown schema at design time.
  • In previous versions, dynamic variables (variables whose type or value can be changed during runtime) and dynamic values (values whose type or schema is determined at runtime) were handled the same way. When either a dynamic value or a dynamic variable was used in a Power Fx expression, a warning was triggered: "Deferred type provided." These warnings occurred because Power Fx enforces strict type schemas (strongly defined types). Starting with this version, we distinguished between these two cases. While dynamic variables continue to generate the "deferred type" warning, dynamic values are now treated as untyped objects.
  • All data table variables are untyped, while custom objects resulting from Convert JSON to a custom object action are untyped. Lists will become untyped after manipulating them with Power Automate for desktop actions from the Variables category.
  • Previously, certain automation actions from the standard library of actions, such as Read from Excel, Read from CSV, Extract data from a web, Extract data from window, Execute SQL statement, and Convert JSON to a custom object would produce a dynamic variable, along with a "deferred type" warning. They now produce an untyped data table or untyped custom object variable instead.
• Set Power Fx function is now enabled but not fully supported yet. While it can't be used to modify a variable's value directly, it can be used with the above structures to also update custom object properties and values of lists in specific indexes (for example, =Set(Index(Index(DataTable, 1), 1), 42) or =Set(customObject.property, 17)).
• Fixed an issue with accessing nested list properties of an object in Power Fx enabled flows.

2.43

In April 2024 release:

• Case sensitivity. For example, NewVar is a different variable than newVar.
• Run Power Fx expression action is available under the Variables group of actions. Run Power Fx expression allows you to execute expressions directly on data sources.
• Collect, Clear, ClearCollect Power Fx functions are supported in desktop flows.
• Patch Power Fx functions are supported in desktop flows.
• Variables and Power Fx expressions can be used in UI element or web selector syntax.
• Interpolated values can now be included in the syntax of a UI/web element selector. For interpolated strings, you can use this syntax: ${ Power Fx expression }.

2.42

In March 2024 release:

• IntelliSense capabilities are now available for Power Fx enabled desktop flows.
  • Syntax colorization
  • Autocomplete functionality during typing with real time suggestions
  • Signature helpers for Power Fx functions

• Function picker
  • You can access the function picker using the fx button in the skittle when interacting with the respective inputs. All Power Fx functions currently supported for desktop flows are available there.

2.41

In February 2024 release:

• From now on inputs that don't begin with the equals sign (=) are considered as text type values. Numeric and boolean inputs must always begin with the equals sign.
• Inputs now support interpolated strings. To include an interpolated value in an input, use the following syntax: Text before ${variable/ expression} text after.
  • Example: The total number is ${Sum(10, 20)}

2.39

In December 2023 release:

• If the input provided doesn't start with the equals sign, the following rules apply:
  • Numeric values without spaces are interpreted as numeric values.
  • True/ False as input, regardless of case and without spaces are interpreted as boolean values.
  • All other inputs are considered of text type values.