Is this the F# Builder bug or my misunderstanding?

f#

Solution

No it's a bug in your code. You need to add parentheses after "printSomeMessage", otherwise printSomeMessage is a simple value rather than a function.

open System

let printSomeMessage() =        
    printfn "Is this the F# BUG?"    

[<EntryPoint>]
let main args =    
    if args.Length = 2 then
        printSomeMessage()
    else        
        printfn "Args.Length is not two."
    0

Simple values are initialized in the constructor of a module, so you see your code being called when the module is initialized. This is logical when you think about it, the normal case of simple values would be binding a string, integer, or other literal value to an identifier. You would expect this to happen a start up. i.e. the following will be bound at module start up:

let x = 1
let y = "my string"

Problem

When I tried the console programming, I received unexpected result. ``` open System let printSomeMessage = printfn "Is this the F# BUG?" [<EntryPoint>] let main args = if args.Length = 2 then printSomeMessage else printfn "Args.Length is not two." 0 ``` The printSomeMessage function was included in .cctor() function. Here is IL DASM result. ``` .method private specialname rtspecialname static void .cctor() cil managed { // Code size 24 (0x18) .maxstack 4 IL_0000: nop IL_0001: ldstr "Is this the F# BUG\?" IL_0006: newobj instance void class [FSharp.Core]Microsoft.FSharp.Core.PrintfFormat`5<class [FSharp.Core]Microsoft.FSharp.Core.Unit,class [mscorlib]System.IO.TextWriter,class [FSharp.Core]Microsoft.FSharp.Core.Unit,class [FSharp.Core]Microsoft.FSharp.Core.Unit,class [FSharp.Core]Microsoft.FSharp.Core.Unit>::.ctor(string) IL_000b: call !!0 [FSharp.Core]Microsoft.FSharp.Core.ExtraTopLevelOperators::PrintFormatLine<class [FSharp.Core]Microsoft.FSharp.Core.Unit>(class [FSharp.Core]Microsoft.FSharp.Core.PrintfFormat`4<!!0,class [mscorlib]System.IO.TextWriter,class [FSharp.Core]Microsoft.FSharp.Core.Unit,class [FSharp.Core]Microsoft.FSharp.Core.Unit>) IL_0010: dup IL_0011: stsfld class [FSharp.Core]Microsoft.FSharp.Core.Unit '<StartupCode$FSharpBugTest>'.$Program::printSomeMessage@3 IL_0016: pop IL_0017: ret } // end of method $Program::.cctor ``` So, its execution result is like this. ``` Is this the F# BUG? Args.Length is not two. ``` Am I missing some grammar or F# characteristic? Or F# builder’s BUG?

Original source