arwhatever • 2 days ago

if I may elaborate on "everything is an expression," F# allows you to do things like (with apologies for being a tad rusty with the syntax)

  let bar = 
      if foo then  
         7  
      else  
         11
or

  let bar = 
      try
        // code that might throw
        7
      with ex ->
        11
and will ensure that both/all code branches return a compatible type for the `let` binding.

Whereas in C# you have to do like

  int bar;

  if (foo) {
     bar = 7;
  } else {
     bar = 11;
  }
And C# will let you know if you omit the `else` on accident ...

Except that most C# developers do

  int bar = 0; // or some other default value`
to get the red squiggly to go away while they type the rest of the code, unknowingly subverting the compiler's safety check.

This doesn't seem like a big deal given these examples. But it becomes a much bigger deal when the if/else grows super large, becomes nested, etc.

1
DeathArrow • 1 day ago

Also C#:

bar = foo switch

{

   true => 7,

   false => 11

}

1 reply
arwhatever • 1 day ago

Ah yes that is definitely a nice addition to the C# language, albeit still with a couple of shortcomings compared to F#:

1. It doesn’t support code blocks, so if you need multiple lines or statements you have to define a function elsewhere. 2. To get exhaustiveness checking on int-backed enums you have to fiddle with compiler preprocessor directives.

And for #2 any data associated with each enum variant is left implied by C# and has to be inferred from a reading of the surrounding imperative code, whereas in F# the union data structure makes the relationship explicit, and verifiable by the compiler.