Refactor

PrattParser/Example.fs

@@ -0,0 +1,66 @@
+namespace PrattParser
+
+open System
+open System.Globalization
+
+[<RequireQualifiedAccess>]
+module Example =
+    let private atom (inputString : string) (token : Token) : Expr option =
+        match token.Type with
+        | TokenType.ConstInt ->
+            let start, len = token.Trivia
+
+            Int32.Parse (inputString.AsSpan().Slice (start, len), NumberStyles.None, CultureInfo.InvariantCulture)
+            |> Expr.constInt
+            |> Some
+        | TokenType.Var ->
+            let start, len = token.Trivia
+            Some (Expr.var (inputString.Substring (start, len)))
+        | TokenType.Plus
+        | TokenType.Minus
+        | TokenType.Times
+        | TokenType.Factorial
+        | TokenType.If
+        | TokenType.Then
+        | TokenType.Else
+        | TokenType.LeftBracket
+        | TokenType.RightBracket -> None
+
+    let parser =
+        Parser.empty
+        |> Parser.defineAtoms atom
+        |> Parser.withUnaryPostfix TokenType.Factorial (7, ()) Expr.factorial
+        |> Parser.withUnaryPrefix TokenType.Plus ((), 5) id
+        |> Parser.withUnaryPrefix TokenType.Minus ((), 5) Expr.unaryMinus
+        |> Parser.withInfix TokenType.Plus (1, 2) Expr.plus
+        |> Parser.withInfix TokenType.Minus (1, 2) Expr.minus
+        |> Parser.withInfix TokenType.Times (1, 2) Expr.times
+        |> Parser.withBracketLike
+            TokenType.LeftBracket
+            {
+                ConsumeAfterFinalToken = false
+                BoundaryTokens = [ TokenType.RightBracket ]
+                Construct = Seq.exactlyOne >> Expr.paren
+            }
+        |> Parser.withBracketLike
+            TokenType.If
+            {
+                ConsumeAfterFinalToken = true
+                BoundaryTokens = [ TokenType.Then ; TokenType.Else ]
+                Construct =
+                    fun s ->
+                        match s with
+                        | [ ifClause ; thenClause ; elseClause ] -> Expr.ifThenElse ifClause thenClause elseClause
+                        | _ -> failwith "logic error"
+            }
+        |> Parser.withBracketLike
+            TokenType.If
+            {
+                ConsumeAfterFinalToken = true
+                BoundaryTokens = [ TokenType.Then ]
+                Construct =
+                    fun s ->
+                        match s with
+                        | [ ifClause ; thenClause ] -> Expr.ifThen ifClause thenClause
+                        | _ -> failwith "logic error"
+            }