SICP exercise 3.19

2021-09-02T00:00:00+00:00

(define (cycle? l)
  (define (rec l x)
    (cond
      ((null? x) false)
      ((eq? l x) true)
      (true (rec l (cdr x)))))
  (rec l (cdr l)))

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Sample interactive session:

scheme@(guile-user)> (define true #t)
scheme@(guile-user)> (define false #f)
scheme@(guile-user)>
(define (cycle? l)
  (define (rec l x)
    (cond
      ((null? x) false)
      ((eq? l x) true)
      (true (rec l (cdr x)))))
  (rec l (cdr l)))
scheme@(guile-user)> (cycle? '(1 2 3))
$9 = #f
scheme@(guile-user)> (cycle? (make-cycle '(1 2 3)))
$10 = #t

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Raku tuple type annotation

2019-12-29T00:00:00+00:00

# Single Str return value: this works
sub f1(Str $in --> Str) {
  $in;
}

# Tuple of Str as return value: this works
sub f2(Str $in) {
  ($in, $in);
}

# Tuple of Str as return value with type annotation: this doesn't works
sub f2(Str $in --> (Str, Str)) {
  ($in, $in);
}

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Error log is:

1 2	===SORRY!=== Error while compiling /path/to/my/file Malformed return value

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SICP exercise 3.19

Raku tuple type annotation