Just finished an epic #fsharp coding binge this week. It was like plugging my brain directly into the machine. There was almost no impedance mismatch between forming a design intention and expressing it in code. I have never felt so productive.
The project is an internal tool that I can't talk too much about. Basically it's a console app that pulls data from different teams/departments and "joins" it together (normalizing disparate domain terminology) to produce various reports that it can dump to the screen or Excel.
Features that made this really easy:
- Type Providers (ExcelProvider FTW)
- Good old |> operator and your basic List/Seq/Array functions, which make much of the report-building logic look like KQL (more members of the team know KQL than F#)
- Type Providers (ExcelProvider FTW)
- Good old |> operator and your basic List/Seq/Array functions, which make much of the report-building logic look like KQL (more members of the team know KQL than F#)
- Sum types and match/with for domain modeling. It made defining and evolving DSLs super easy.
- Enforced file and declaration ordering, which was a forcing function for factoring the modules/layers correctly. I think of this not as a limitation, but an underappreciated feature.
- Enforced file and declaration ordering, which was a forcing function for factoring the modules/layers correctly. I think of this not as a limitation, but an underappreciated feature.
- Object expressions. I found a nice pattern in the F# style guide for defining service interfaces and implementing them inline in a function like MyServiceModule.create
- Yes, even classes. It felt very natural to use them for services and domain types with run-time validation.
- Yes, even classes. It felt very natural to use them for services and domain types with run-time validation.
I feel like I've really hit a groove here, knowing when to use the functional features and when to use OO. Everything just fits, and nothing felt needlessly difficult.
Maybe my favourite experience was refactoring the report-displaying code from a bunch of messy printfn's into a TabularReport domain object that can be turned into either console output or Excel spreadsheets via implementations of an IReportRenderer interface. MVC for consoles :)
It supports column alignment (kind of a PITA in console apps), type-specific formatting for currency and percentages, and conditional formatting. This sounds hard, but it really wasn't.
For the Excel renderer, much credit goes to ClosedXml, which is an awesome library. closedxml.github.io/ClosedXML/
This was a blast. Now I can rest.
Totally forgot units of measure, which were very applicable to the types of calculations used in generating the reports. I ❤️catching bugs at compile time!
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