What is that "arg00" in the type of Fsharp.Text.Lexing's LexBuffer<char>.LexemeString?
> LexBuffer<char>.LexemeString;;
val it : arg00:LexBuffer<char> -> string
The short answer is that F# can sometimes keep track of argument names when printing the type of a function. In this case, arg00 is an implicit name generated by the compiler for the first argument of the LexemeString operation.
The longer answer is that F# is a bit inconsistent when dealing with function arguments. If you define a function using let, the output will include arguments:
> let foo a b = a + b;;
val foo : a:int -> b:int -> int
If you just a function as a value through its name, the result is treated as a function value (with parentheses around it) and the argument names are omitted:
> foo;;
val it : (int -> int -> int) = <fun:it@4-2>
However, if you define a static member and access it, then the compiler still attempts to print the argument names, but cannot access them (because the member has now been turned into a value) and so it prints implicitly generated names like arg00:
> type A =
static member Foo a b = a + b;;
type A = (...)
> A.Foo;;
val it : arg00:int -> arg10:int -> int