Add spaces before uppercase letters I'm trying to convert some very simple C# string utility functions to F# as a learning exercise. Ignore the fact that the C# version is implemented as an extension method for the moment. 

The function adds a blank space before any upper case letters (with the exception of the very first char) - so, "ATestString" becomes "A Test String":

return string.Concat(str.Select(x =&gt; Char.IsUpper(x) ? " " + x : x.ToString())).TrimStart(' ');


My first pass using F#:

let padWithSpace str = 
    (str |&gt; Seq.fold (fun acc elm -&gt; if Char.IsUpper(elm) then acc + (sprintf " %c" &lt;| elm) else acc + (string elm)) "").TrimStart([| ' ' |])


Is there a more concise, or more importantly, idiomatic way to do this in F#?
String.collect is equivalent to Select+Concat.

let padWithSpace = 
    String.collect (fun c -&gt; (if Char.IsUpper c then " " else "") + string c) 
    &gt;&gt; fun s -&gt; s.TrimStart()