Lexer in Racket

lever.rkt

#lang typed/racket
(require racket/list)


(define (operator c )
  (match c
     ['+' Plus]
     ['-' Minus]
     ['/' Div]))

(struct (i) Literal ([v : i]))
(struct Plus ())
(struct Minus ())
(struct Div ())
(struct (i) InvalidChar ([v : i]))

(struct EndOfInput())
(struct Empty() )
(struct (i) Unexpected([val : i]))
(define-type (Expected i e) (U Integer Char))
(struct (i)  ExpectedEndOfFile([val : i]))
(struct  (i) BeginningOfInput ([val : i]))

(define-type (ErrorType i e)
      (U Empty EndOfInput
      ( Unexpected i)
      ( Expected i e)
      ( ExpectedEndOfFile i)
      ( BeginningOfInput i)))

(define-type (Error i e) (U Integer
                            (ErrorType i e)))