Int32.TryParse and F#+ tryParse give different results

Description

Basically (tested with culture on en-US).

> let value: int option = tryParse "123,45";;
val value: int option = Some 12345

> Int32.TryParse "123,45";;
val it: bool * int = (false, 0)

In other words, integers cannot have thousand-separators with Int32.TryParse, but can with tryParse.

Conversely, it doesn’t allow decimals, which is good:

> let value: int option = tryParse "123.45";;
val value: int option = None

> Int32.TryParse "123.45";;
val it: bool * int = (false, 0)

Likewise there’s a similar difference with e-notation:

> let value: int option = tryParse "12345e4";;
val value: int option = Some 123450000

> Int32.TryParse "12345e4";;
val it: bool * int = (false, 0)

Repro steps

See above.

Expected behavior

From the description of the method, you’d expect the same behavior as the .NET functions, but they allow certain illegal values, or at least ambiguous, considering how .NET parses numbers.

Actual behavior

See above. This is caused by NumberStyles.Any, which is not used by Int32.TryParse or Decimal.TryParse. These use NumberStyles.Integer and NumberStyles.Decimal respectively (see source of .NET), which limit the allowed range.

Known workarounds

Create your own types or call Int32.TryParse directly, or create your own helper function.

Related information

Most recent F#+ and tested with .NET 6, but assuming it is the same on .NET 7.

[abelbraaksma]

Related: regardless of whether we’d fix this issue or not, perhaps we can update the documentation to specify that parse and tryParse uses InvariantCulture. Currently, it not being mentioned, may lead people to believe it works the same as XXX.Parse/TryParse from the BCL, that is, that it changes behavior depending on the current culture.

[abelbraaksma]

I would set the defaults to what I wrote before:

we should stay as close as possible to what .NET itself implements, to stick with the “principle of least suprised”.

not sure if parseStrict is the ideal choice, but I can’t think of anything better right now.