The first is almost certainly better off as it is in F#: active patterns. That'll let you define patterns that'll execute arbitrary code to match, making regex

The first is almost certainly better off as it is in F#: active patterns. That'll let you define patterns that'll execute arbitrary code to match, making regex a simple library feature, vs a special one-off. C# should have focused on having proper extensible syntax vs hard coding random features (like duck typed foreach or collection initializers). But given the constraints of mscorp and the target users perhaps they made the right decisions.