I'm looking at this from
https://github.com/dparpyani/99-Lisp-Problems-in-Racket:
#lang racket
(require typed/racket)
;; Question:
;; Find the last box of a list.
;; Example:
;; (my-last '(a b c d))
;; => '(d)
;; Consumes a list and returns the last element in it.
(define (my-last lst)
(cond
[(or (empty? lst) (empty? (rest lst))) lst]
[else (my-last (rest lst))]))
;; Tests
(assert (equal? (my-last `(a b c d)) `(d)))
(assert (equal? (my-last `(1 2 3 4)) `(4)))
(assert (equal? (my-last `((a b) (c d))) `((c d))))
...which seems to behave fine when loaded from the command line, i.e.,
#> racket Q01.rkt
#t
#t
#t
However, when loaded from with a Racket REPL
> (load "Q01.rkt")
> (my-last '(1 2 3))
; readline-input:14:1: Type Checker: missing type for top-level identifier;
; either undefined or missing a type annotation
; identifier: my-last
; in: my-last
; [,bt for context]
Likewise, simply entering everything in the REPL also fails:
> (require typed/racket)
> (define (my-last lst)
(cond
[(or (empty? lst) (empty? (rest lst))) lst]
[else (my-last (rest lst))]))
; readline-input:18:30: Type Checker: Polymorphic function `rest' could not be
; applied to arguments:
; Domains: (Listof a)
; (Pairof a (Listof b))
; Arguments: Any
; in: (rest lst)
; [,bt for context]
Why the different behaviors? All I'm trying to do is use assert. But then how
would I change this code to be typed Racket?
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