{"id":7541,"date":"2022-11-28T06:00:04","date_gmt":"2022-11-28T04:00:04","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=7541"},"modified":"2022-12-14T11:30:34","modified_gmt":"2022-12-14T09:30:34","slug":"28-nov-22","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/28-nov-22\/","title":{"rendered":"El tipo de las listas"},"content":{"rendered":"

El tipo de las listas, con elementos de tipo a, se puede definir por<\/p>\n

\n   data Lista a = Nil | Cons a (Lista a)\n<\/pre>\n
Por ejemplo, la lista [4,2,5]<\/code> se representa por Cons 4 (Cons 2 (Cons 5 Nil))<\/code>.<\/p>\n
Definir la funci\u00f3n<\/p>\n
\n   longitud :: Lista a -> Int\n<\/pre>\n
tal que longitud xs<\/code> es la longitud de la lista xs<\/code>. Por ejemplo,<\/p>\n
\n   longitud (Cons 4 (Cons 2 (Cons 5 Nil)))  ==  3\n<\/pre>\n
Soluciones<\/b><\/p>\n
A continuaci\u00f3n se muestran las soluciones en Haskell<\/a> y las soluciones en Python<\/a>.<\/p>\n
<\/a>
\nSoluciones en Haskell<\/b><\/p>\n
\ndata Lista a = Nil | Cons a (Lista a)\n\nlongitud :: Lista a -> Int\nlongitud Nil         = 0\nlongitud (Cons _ xs) = 1 + longitud xs\n<\/pre>\n
<\/a>
\nSoluciones en Python<\/b><\/p>\n
\nfrom dataclasses import dataclass\nfrom typing import Generic, TypeVar\n\nA = TypeVar(\"A\")\n\n@dataclass\nclass Lista(Generic[A]):\n    pass\n\n@dataclass\nclass Nil(Lista[A]):\n    pass\n\n@dataclass\nclass Cons(Lista[A]):\n    x: A\n    xs: Lista[A]\n\ndef longitud(xs: Lista[A]) -> int:\n    match xs:\n        case Nil():\n            return 0\n        case Cons(_, xs):\n            return 1 + longitud(xs)\n    assert False\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
El tipo de las listas, con elementos de tipo a, se puede definir por data Lista a = Nil | Cons a (Lista a) Por ejemplo, la lista [4,2,5] se representa por Cons 4 (Cons 2 (Cons 5 Nil)). Definir la funci\u00f3n longitud :: Lista a -> Int tal que longitud xs es la longitud…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_kad_post_transparent":"","_kad_post_title":"","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"footnotes":"","_jetpack_memberships_contains_paid_content":false},"categories":[581],"tags":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/7541"}],"collection":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/comments?post=7541"}],"version-history":[{"count":2,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/7541\/revisions"}],"predecessor-version":[{"id":7639,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/7541\/revisions\/7639"}],"wp:attachment":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/media?parent=7541"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/categories?post=7541"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/tags?post=7541"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}