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| Ambos lados, revisión anterior Revisión previa Próxima revisión | Revisión previa | ||
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wiki2:elm-code [2020/12/25 13:29] alfred [Gotchas] |
wiki2:elm-code [2020/12/26 08:03] (actual) |
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| Línea 15: | Línea 15: | ||
| priceInEuros 3.3 -- 3.63 | priceInEuros 3.3 -- 3.63 | ||
| </code> | </code> | ||
| - | ==== Function composition (?) ==== | + | ==== Partially applied functions ==== |
| Every function that accepts two arguments can be converted in one that accepts one argument: | Every function that accepts two arguments can be converted in one that accepts one argument: | ||
| Línea 26: | Línea 26: | ||
| </code> | </code> | ||
| + | Then there is this: | ||
| + | <code> | ||
| + | double = (*) 2 | ||
| + | <function> : number -> number | ||
| + | </code> | ||
| + | This can happen because all functions accept only and exactly one argument. | ||
| - | ==== Simplify types ==== | + | <code> |
| + | > greeting : String -> String -> String | ||
| + | | greeting greet name = greet ++ ", " ++ name ++ "!" | ||
| + | <function> : String -> String -> String | ||
| + | > greeting "Hello" "DailyDrip" == ((greeting "Hello") "DailyDrip") | ||
| + | True : Bool | ||
| + | </code> | ||
| - | type alias MyType = Int -> String -> String | + | Parentheses are optional because function evaluation associates to the left by default. |
| - | mytrial: MyType | + | |
| - | mytrial n s = String.repeat n s | + | <code> |
| - | mytrial 3 "abc" | + | > (*) |
| + | <function> : number -> number -> number | ||
| + | double = (*) 2 | ||
| + | <function> : number -> number | ||
| + | </code> | ||
| + | As we can see we can think that (*) takes two numbers as arguments. On double function the compiler will really infer that our double function takes one number as its sole argument. | ||
| + | |||
| + | Then we can easily create a function for doubling values on a list: | ||
| + | <code> | ||
| + | doubleList = List.map double | ||
| + | -- <function> : List number -> List number | ||
| + | </code> | ||
| + | |||
| + | This is the main reason why [[https://package.elm-lang.org/help/design-guidelines#the-data-structure-is-always-the-last-argument|the data structure should be always the last argument]]. | ||
| + | |||
| + | He have also this: | ||
| + | <code> | ||
| + | > (|>) | ||
| + | <function> : a -> (a -> b) -> b | ||
| + | |||
| + | amountDeposited : List Transaction -> Float | ||
| + | amountDeposited list = | ||
| + | List.filter (\t -> t.type_ == Deposit) list | ||
| + | |> List.map .amount | ||
| + | |> List.sum | ||
| + | |||
| + | -- It filters all the transactions in list which are deposits and obtain the amount for, at the last step, sum them. | ||
| + | -- rather than the nested equivalent: | ||
| + | -- List.sum (List.map .amount (List.filter (\t -> t.type_ == Deposit) list)) | ||
| + | </code> | ||
| + | ==== Simplify types ==== | ||
| + | <code> | ||
| + | > type alias MyType = Int -> String -> String | ||
| + | > mytrial: MyType | ||
| + | | mytrial n s = String.repeat n s | ||
| + | <function> : Int -> String -> String | ||
| + | > mytrial 3 "abc" | ||
| + | "abcabcabc" : String | ||
| + | </code> | ||
wiki2/elm-code.1608902975.txt.gz · Última modificación: 2020/12/25 14:29 (editor externo)
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