F# Interactive emits debug symbols.

(a) To get line information in exceptions, you have to be loading from a file, like "fsi foo.fsx" or a #load, or else #line directives must be emitted by the script or tool hosting F# Interactive. The #line directives are inserted autoatically by Visual Studio and Xamarin Studio.

(b) Line information seem to be missing for exceptions from top-level initialization code.

(c) inlining and optimization may affect the accuracy of line information

Example:

#line 3 @"abc.fs"

let f() =
printfn "hello"
printfn "hello"
printfn "hello"
printfn "hello"
printfn "hello"
(failwith "x" : int)

f()

System.Exception: x
at FSI_0004.f() in C:\test\abc.fs:line 9
at <StartupCode$FSI_0004>.$FSI_0004.main@()

Note the "line 9" on the second last line