more code

Pentole/pervasives.fs

@@ -1,5 +1,6 @@
 namespace Pentole
 
+/// The initially opened module. 
 [<AutoOpen>]
 module Pervasives =
 
@@ -7,3 +8,10 @@ module Pervasives =
     /// The identity function.
     /// </summary>
     let identity = id
+
+    /// An active pattern that matches strings starting with a specified prefix.
+    let (|Prefix|_|) (p: string) (s: string) =
+        if s.StartsWith p then
+            s.Substring p.Length |> Some
+        else
+            None

Pentole/string.fs

@@ -1,4 +1,6 @@
-module Pentole.String
+namespace Pentole
+
+module String =
 
     let split (separator: string) (target: string) : string list =
         if System.String.IsNullOrEmpty separator  then

Pentole/test_extensions.fs

@@ -2,6 +2,8 @@ namespace Pentole
 
 open NUnit.Framework
 
+type TestAttribute = NUnit.Framework.TestAttribute
+
 module Assert =
     let inline okEquals<'ok, 'err> (expected: 'ok) (got: Result<'ok, 'err>) =
         match got with