The bulk of F# is functions acting on values modeled by types. This maps directly to JS. In the F# and .NET compatibility document, you'll note that all "core F#" components map directly to JS. And of course, you can consume JS libraries, TS definition files, etc. For example:
"The following F# semantic and syntactic features are also available:
* Records and Unions
* Structural Equality/Comparison
* Comprehensions (seq, array, list)
* Computation Expressions
* Pattern Matching
* Active Patterns
* Object Expressions
* Units of measure"
Do you have specific examples where F# semantics cannot map to JS such that the "80% rule" also does not hold?
> Do you have specific examples where F# semantics cannot map to JS such that the "80% rule" also does not hold?
Yes, my comment was around some of the C# compatibility things, which don't make sense when compiling to other targets.
> Tuples vs struct tuples distinction.
> Having both modules and namespaces
> Explicit interfaces
> The strange coupling of SRTP and inlining
I find OCaml's support for structural typing in classes and polymorphism to be more flexible than the above.
In typed FP, runtime reflection is seldom used, and I believe reflection support (and associated overhead) should have to be explicitly opted in.
I also faced weird issues when tracing the source of an exception in an async workflow, and some incomprehensible errors around automatic generalization. But this was a long time back and I no longer have the full context. These may have since been addressed.
My intent was certainly not to criticise F#. It has been developed and is used by people far smarter than me. It is just that after a preliminary evaluation I have not found a strong reason to prefer Fable over bucklescript in the absence of a more deeper commitment to dotnet stack.
I am also really fond of many modern JS features like Module <-> Filepath 1:1 correlation, explicit imports, ES6 proxies, tagged template literals (placeholders etc.) which TypeScript elegantly inherits from JS. Support for intersection types in typescrpt is also very handy.