An warware: shugaban lissafin

Haskell babban yaren shirye-shirye ne kawai, wanda ya shahara saboda sauƙaƙansa da kyawunsa.. Madaidaicin ɗakin karatu yana ba da ɗimbin ayyuka da nau'ikan bayanai, gami da jeri, waɗanda ke da mahimmanci ga yawancin ayyukan shirye-shirye a Haskell. Matsala ɗaya da aka saba fuskanta a cikin shirye-shiryen Haskell ta haɗa da samun dama ga shugaban lissafi, watau kashi na farko a lissafin. Wannan aiki da alama mai sauƙi zai iya haifar da kurakurai na lokacin aiki idan ba a kula da su daidai ba. A cikin wannan cikakkiyar jagorar, za mu zurfafa cikin matsalar samun damar kan lissafin, mu bayyana ingantacciyar hanyar warwarewa, sannan mu ɗauke ku ta hanyar lambar da ke da alaƙa, mataki-mataki.

Matsalar da muke son warwarewa ita ce yadda za mu sami shugaban lissafin a Haskell lafiya. Wannan batu ya taso ne saboda daidaitaccen aikin kai na Haskell yana da ban sha'awa, wanda ke nufin ba a bayyana shi ga kowane shigarwar da zai yiwu ba. Musamman, yana kasawa akan lissafin fanko. Manufarmu ita ce ƙirƙirar aikin da yake gabaɗaya, ma'ana yana ɗaukar kowane shigarwar da zai yiwu, gami da lissafin fanko.

safeHead :: [a] -> Maybe a
safeHead []     = Nothing
safeHead (x:xs) = Just x

Wannan aikin safeHead ba zai dawo da komai ba idan lissafin fanko ne, kuma kawai x (tare da x shine abu na farko) idan lissafin ba komai bane. Anan, Watakila a nau'i ne da ke wakiltar ƙimar zaɓi: kowane Watakila ƙima ba komai ba ce ko kuma tana ɗauke da ƙimar nau'in a kawai.

Fahimtar Code: Mataki-mataki

Mun tsara aikin mu na safeHead don sarrafa duk abubuwan da za a iya shigar da su, bin ƙa'idodin Haskell da shirye-shirye masu aiki: sarrafa duk dama kai tsaye, guje wa illa, da haɓaka iya karanta lambar.

Da farko, muna ayyana sa hannun nau'in aikin, safeHead :: [a] -> Wataƙila a. Wannan yana nufin aikin yana ɗaukar jerin kowane nau'i ([a]) kuma yana dawo da nau'in Wataƙila. Yana da mahimmanci a tuna da tsarin nau'in ƙarfi na Haskell, inda kowane magana a cikin Haskell yana da nau'i wanda aka ƙaddara a lokacin tattarawa.

Ana aiwatar da aikin mu ta amfani da daidaitawar ƙirar, mahimmin fasalin Haskell.

safeHead []     = Nothing
safeHead (x:xs) = Just x

Anan, ''[]' yayi daidai da lissafin fanko, don haka ba mu dawo da komai ba. '(x:xs)' yayi daidai da jerin marasa fanko tare da kai 'x' da wutsiya'xs' kuma mu dawo 'Just x'.

Tallafin Laburare da Sauran Ayyuka

Nau'in Wataƙila wani ɓangare ne na daidaitaccen ɗakin karatu na Haskell kuma yana ba masu shirye-shirye damar magance ƙimar da ba a bayyana ba ko kuma kula da lamuran irin namu inda aikin ƙila ba shi da ƙayyadaddun ƙimar dawowa ga duk abubuwan da za a iya samu. A halin yanzu, ana iya tsawaita aikin safeHead ta halitta don gudanar da ƙarin ayyukan sarrafa jeri cikin aminci.

Misali, ana iya bayyana aikin safeTail kamar haka:

safeTail :: [a] -> Maybe [a]
safeTail []     = Nothing
safeTail (x:xs) = Just xs

Kamar aikin mu na safeHead, safeTail ba zai dawo da komai ba don jerin fanko kuma kawai xs (jerin ya rage kashinsa na farko) in ba haka ba. Bayan mun rufe manufar samun damar jeri mai aminci a cikin Haskell, bari mu matsa kayan aiki kuma mu zurfafa cikin fagen salon salo inda zaɓi da haɗe-haɗe za su iya zama kamar hadaddun da wadata kamar a cikin shirye-shirye masu aiki.