Command Line Tools

Okay, so I'm going to start by inspecting the command line tools for F#. This depends on whether you're using .NET or mono. For mono:

fsharpc == command line compiler
fsharpi == command line interactive (REPL)

For .NET:

fsc.exe == command line compiler
fsi.exe == command line interactive (REPL)

So I'll start by messing around with the interpreter. A REPL is a hugely beneficial tool when learning a language or trying out code you don't understand. It won't take me too far, because doing anything complicated requires more flexibility, but it's a great way to test understanding. 

I'm also going to use the tutorials over at Try F#. You can do the same if you like. Okay, I'm ready to learn some basics!

Matthews-MacBook-Pro:~ Matthew$ fsharpi

The REPL tells me I can get help with the command #help;; so I'll try that first. Here are a few fundamentals of the REPL:

• Every statement or block needs to be followed with ;;. This tells the REPL to process the command. This doesn't seem to be part of the language,  just a convention of the interactive F#.
• The REPL responds to commands that start with a hash mark. It took me a minute to figure this out, because I didn't use #help;;. Be smarter than me and use the help menu!
• #help;;  Access the help menu. 
• #quit;;  Quit the REPL.
• #r "File.dll";;  
• Assuming that the "r" stands for reference; allows you to reference a dll. I'll take that for a spin.
• #I "path";;  
• Looks like you can add a path to include dlls. 
• #load "file.fs" ...;; 
• If I want to load a script and then play around with it in the REPL, this command should do that for me.
• #time ["on"|"off"];; 
• No idea.  Maybe this gives you stopwatch data about the executing code?

I'm curious about that #time;; option so I'll try that first. 

> #time "on";;

--> Timing now on

> let me = "spotaneous";;

Real: 00:00:00.000, CPU: 00:00:00.003, GC gen0: 0, gen1: 0

val me : string = "spotaneous"

That's pretty cool! So I can do some primitive optimization in the REPL by comparing the timing of different code options. It's not something I need right away, but cool nonetheless.

It's worth noting that this is how the REPL reports the value of a reference:

val me : string = "spotaneous"

It looks a little confusing to me, since it looks suspiciously like a variable assignment in another language, but it's not. I can check the value referenced by:

> me;;

Real: 00:00:00.000, CPU: 00:00:00.000, GC gen0: 0, gen1: 0

val it : string = "spotaneous"

See Also:

Referencing a dll interactively
Loading an external F# file interactively