{"id":2256,"date":"2016-03-29T06:00:29","date_gmt":"2016-03-29T04:00:29","guid":{"rendered":"http:\/\/www.glc.us.es\/~jalonso\/exercitium\/?p=2256"},"modified":"2022-03-26T12:12:07","modified_gmt":"2022-03-26T10:12:07","slug":"evaluacion-de-expresiones-aritmeticas","status":"publish","type":"post","link":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/evaluacion-de-expresiones-aritmeticas\/","title":{"rendered":"Evaluaci\u00f3n de expresiones aritm\u00e9ticas"},"content":{"rendered":"<p>Las expresiones aritm\u00e9ticas se pueden definir mediante el siguiente tipo de dato<\/p>\n<pre lang=\"text\">\n   data Expr  = N Int | V Char | Sum Expr Expr | Mul Expr Expr \n                deriving Show\n<\/pre>\n<p>Por ejemplo, (x+3)+(7*y) se representa por<\/p>\n<pre lang=\"text\">\n   ejExpr :: Expr\n   ejExpr = Sum (Sum (V 'x') (N 3))(Mul (N 7) (V 'y')) \n<\/pre>\n<p>Definir la funci\u00f3n<\/p>\n<pre lang=\"text\">\n   valor :: Expr -> Maybe Int\n<\/pre>\n<p>tal que (valor e) es &#8216;Just v&#8217; si la expresi\u00f3n e es num\u00e9rica y v es su valor, o bien &#8216;Nothing&#8217; si e no es num\u00e9rica. Por ejemplo:<\/p>\n<pre lang=\"text\">\n   valor (Sum (N 7) (N 9))                            == Just 16\n   valor (Sum (Sum (V 'x') (N 3))(Mul (N 7) (V 'y'))) == Nothing\n   valor (Sum (Sum (N 1) (N 3))(Mul (N 7) (N 2)))     == Just 18\n<\/pre>\n<h4>Soluciones<\/h4>\n<pre lang=\"haskell\">\ndata Expr  = N Int | V Char | Sum Expr Expr | Mul Expr Expr \n             deriving Show\n\n-- 1\u00aa soluci\u00f3n\n-- ===========\n\nvalor1 :: Expr -> Maybe Int\nvalor1 e | null (aux e) = Nothing\n         | otherwise    = Just (head (aux e))\n    where aux (N x)       = [x]\n          aux (V _)       = []\n          aux (Sum e1 e2) = [x+y| x <- aux e1, y <- aux e2]\n          aux (Mul e1 e2) = [x*y| x <- aux e1, y <- aux e2]\n\n-- 2\u00aa soluci\u00f3n\n-- ===========\n\nvalor2 :: Expr -> Maybe Int\nvalor2 e | numerico e = Just (aux e)\n         | otherwise  = Nothing\n    where aux (N x)       = x\n          aux (Sum e1 e2) = aux e1 + aux e2\n          aux (Mul e1 e2) = aux e1 * aux e2\n\nnumerico :: Expr -> Bool\nnumerico (N _)       = True\nnumerico (V _)       = False\nnumerico (Sum e1 e2) = numerico e1 && numerico e2\nnumerico (Mul e1 e2) = numerico e1 && numerico e2\n<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>Las expresiones aritm\u00e9ticas se pueden definir mediante el siguiente tipo de dato data Expr = N Int | V Char | Sum Expr Expr | Mul Expr Expr deriving Show Por ejemplo, (x+3)+(7*y) se representa por ejExpr :: Expr ejExpr = Sum (Sum (V &#8216;x&#8217;) (N 3))(Mul (N 7) (V &#8216;y&#8217;)) Definir la funci\u00f3n valor&#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":[4],"tags":[500,71,141,6,133],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/2256"}],"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=2256"}],"version-history":[{"count":3,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/2256\/revisions"}],"predecessor-version":[{"id":2295,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/posts\/2256\/revisions\/2295"}],"wp:attachment":[{"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/media?parent=2256"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/categories?post=2256"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glc.us.es\/~jalonso\/exercitium\/wp-json\/wp\/v2\/tags?post=2256"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}