Day 1 in F#

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/EfficientString.fs

@@ -0,0 +1,97 @@
+namespace AdventOfCode2023
+
+open System
+open System.Globalization
+open System.Runtime.CompilerServices
+
+type EfficientString = System.ReadOnlySpan<char>
+
+[<RequireQualifiedAccess>]
+module EfficientString =
+
+    let inline isEmpty (s : EfficientString) : bool = s.IsEmpty
+
+
+    let inline ofString (s : string) : EfficientString = s.AsSpan ()
+
+    let inline toString (s : EfficientString) : string = s.ToString ()
+
+    let inline trimStart (s : EfficientString) : EfficientString = s.TrimStart ()
+
+    let inline slice (start : int) (length : int) (s : EfficientString) : EfficientString = s.Slice (start, length)
+
+    let inline equals (a : string) (other : EfficientString) : bool =
+        MemoryExtensions.Equals (other, a.AsSpan (), StringComparison.Ordinal)
+
+    /// Mutates the input to drop up to the first instance of the input char,
+    /// and returns what was dropped.
+    /// If the char is not present, deletes the input.
+    let takeUntil<'a> (c : char) (s : EfficientString byref) : EfficientString =
+        let first = s.IndexOf c
+
+        if first < 0 then
+            let toRet = s
+            s <- EfficientString.Empty
+            toRet
+        else
+            let toRet = slice 0 first s
+            s <- slice (first + 1) (s.Length - first - 1) s
+            toRet
+
+[<Struct>]
+[<IsByRefLike>]
+type StringSplitEnumerator =
+    internal
+        {
+            Original : EfficientString
+            mutable Remaining : EfficientString
+            mutable InternalCurrent : EfficientString
+            SplitOn : char
+        }
+
+    interface IDisposable with
+        member this.Dispose () = ()
+
+    member this.Current : EfficientString = this.InternalCurrent
+
+    member this.MoveNext () =
+        if this.Remaining.Length = 0 then
+            false
+        else
+            this.InternalCurrent <- EfficientString.takeUntil this.SplitOn &this.Remaining
+            true
+
+    member this.GetEnumerator () = this
+
+[<RequireQualifiedAccess>]
+module StringSplitEnumerator =
+
+    let make (splitChar : char) (s : string) : StringSplitEnumerator =
+        {
+            Original = EfficientString.ofString s
+            Remaining = EfficientString.ofString s
+            InternalCurrent = EfficientString.Empty
+            SplitOn = splitChar
+        }
+
+    let make' (splitChar : char) (s : ReadOnlySpan<char>) : StringSplitEnumerator =
+        {
+            Original = s
+            Remaining = s
+            InternalCurrent = EfficientString.Empty
+            SplitOn = splitChar
+        }
+
+    let chomp (s : string) (e : byref<StringSplitEnumerator>) : unit =
+#if DEBUG
+        if not (e.MoveNext ()) || not (EfficientString.equals s e.Current) then
+            failwithf "expected '%s', got '%s'" s (e.Current.ToString ())
+#else
+        e.MoveNext () |> ignore
+#endif
+
+    let consumeInt (e : byref<StringSplitEnumerator>) : int =
+        if not (e.MoveNext ()) then
+            failwith "expected an int, got nothing"
+
+        Int32.Parse e.Current