Re: [Chicken-janitors] #1533: Scrutinizer seems to get confused about list length

[Chicken Trac]

#1533: Scrutinizer seems to get confused about list length
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            Reporter:  sjamaan      |      Owner:
                Type:  defect       |     Status:  new
            Priority:  major        |  Milestone:  5.0
           Component:  scrutinizer  |    Version:  5.0.0rc2
          Resolution:               |   Keywords:  flow analysis
Estimated difficulty:  hard         |
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Comment (by megane):

 There's at least two things going on here.

 First is type smashing. The calls to `usage`, which has unknown type
 smashes the type of `args` to `(or pair null)`. This can be avoided by
 moving the `usage` calls to tail call positions.

 In theory, defining `usage` like this should help:
 {{{
 (define usage
   (the (#!optional fixnum -> noreturn)
         (lambda (#!optional exit-code)
           (when exit-code
             (exit exit-code)))))
 }}}

 But doesn't, for some reason.

 Secondly, there's an issue with refinement:
 {{{
 (import scheme (chicken base) (chicken type))

 (let ([a (the (or pair null) (cons 1 '()))])
   (length a) ; refine (or pair null) with list (= (or pair null))
   (compiler-typecase a ((not *) 1)))
 ;;
 ;; Error: at toplevel:
 ;;   (hoi.scm:33) no clause applies in `compiler-typecase' for expression
 of type `null':
 ;;     (not *)

 }}}
 The type should stay `(or pair null)`, but is refined to `null`.

--
Ticket URL: <https://bugs.call-cc.org/ticket/1533#comment:1>
CHICKEN Scheme <https://www.call-cc.org/>
CHICKEN Scheme is a compiler for the Scheme programming language.