{"id":7777,"date":"2023-01-11T06:00:24","date_gmt":"2023-01-11T04:00:24","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=7777"},"modified":"2022-12-30T12:45:22","modified_gmt":"2022-12-30T10:45:22","slug":"11-ene-23","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/11-ene-23\/","title":{"rendered":"Valor de una expresi\u00f3n aritm\u00e9tica con variables"},"content":{"rendered":"<p>Las expresiones aritm\u00e9ticas con variables pueden representarse usando el siguiente tipo de datos<\/p>\n<pre lang=\"text\">\n   data Expr = C Int\n             | V Char\n             | S Expr Expr\n             | P Expr Expr\n<\/pre>\n<p>Por ejemplo, la expresi\u00f3n <code>2\u00b7(a+5)<\/code> se representa por<\/p>\n<pre lang=\"text\">\n   P (C 2) (S (V 'a') (C 5))\n<\/pre>\n<p>Definir la funci\u00f3n<\/p>\n<pre lang=\"text\">\n   valor :: Expr -> [(Char,Int)] -> Int\n<\/pre>\n<p>tal que <code>valor x e<\/code> es el valor de la expresi\u00f3n <code>x<\/code> en el entorno <code>e<\/code> (es decir, el valor de la expresi\u00f3n donde las variables de <code>x<\/code> se sustituyen por los valores seg\u00fan se indican en el entorno <code>e<\/code>). Por ejemplo,<\/p>\n<pre lang=\"text\">\n   \u03bb> valor (P (C 2) (S (V 'a') (V 'b'))) [('a',2),('b',5)]\n   14\n<\/pre>\n<p><b>Soluciones<\/b><\/p>\n<p>A continuaci\u00f3n se muestran las <a href=\"#haskell\">soluciones en Haskell<\/a> y las <a href=\"#python\">soluciones en Python<\/a>.<\/p>\n<p><a name=\"haskell\"><\/a><br \/>\n<b>Soluciones en Haskell<\/b><\/p>\n<pre lang=\"haskell\">\ndata Expr = C Int\n          | V Char\n          | S Expr Expr\n          | P Expr Expr\n\nvalor :: Expr -> [(Char,Int)] -> Int\nvalor (C x)   _ = x\nvalor (V x)   e = head [y | (z,y) <- e, z == x]\nvalor (S x y) e = valor x e + valor y e\nvalor (P x y) e = valor x e * valor y e\n<\/pre>\n<p><a name=\"python\"><\/a><br \/>\n<b>Soluciones en Python<\/b><\/p>\n<pre lang=\"python\">\nfrom dataclasses import dataclass\n\n\n@dataclass\nclass Expr:\n    pass\n\n@dataclass\nclass C(Expr):\n    x: int\n\n@dataclass\nclass V(Expr):\n    x: str\n\n@dataclass\nclass S(Expr):\n    x: Expr\n    y: Expr\n\n@dataclass\nclass P(Expr):\n    x: Expr\n    y: Expr\n\ndef valor(e: Expr, xs: list[tuple[str, int]]) -> int:\n    match e:\n        case C(a):\n            return a\n        case V(x):\n            return [y for (z, y) in xs if z == x][0]\n        case S(e1, e2):\n            return valor(e1, xs) + valor(e2, xs)\n        case P(e1, e2):\n            return valor(e1, xs) * valor(e2, xs)\n    assert False\n<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>Las expresiones aritm\u00e9ticas con variables pueden representarse usando el siguiente tipo de datos data Expr = C Int | V Char | S Expr Expr | P Expr Expr Por ejemplo, la expresi\u00f3n 2\u00b7(a+5) se representa por P (C 2) (S (V &#8216;a&#8217;) (C 5)) Definir la funci\u00f3n valor :: Expr -> [(Char,Int)] -> Int&#8230;<\/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":[582],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/7777"}],"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=7777"}],"version-history":[{"count":1,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/7777\/revisions"}],"predecessor-version":[{"id":7778,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/7777\/revisions\/7778"}],"wp:attachment":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/media?parent=7777"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/categories?post=7777"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/tags?post=7777"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}