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| 1 | +# Elm syntax basics 2 |
| 2 | + |
| 3 | +## Exporting functions |
| 4 | + |
| 5 | +Exporting functions was covered in the first concept, here is a quick refresher. |
| 6 | + |
| 7 | +Each file in Elm is a module and must contain a `module` statement before all other code. |
| 8 | + |
| 9 | +Module names must match their file name, so module `Calculator` must be in file Calculator.elm, and module `Parser.Utils` needs to be in file Parser/Utils.elm. |
| 10 | + |
| 11 | +Anything defined within a module is privatly scoped to it and cannot be accessed from outside this module, unless listed in `exposing`. |
| 12 | + |
| 13 | +```elm |
| 14 | +-- Calculator.elm |
| 15 | +-- Define the Calculator module, and expose the `add` function |
| 16 | +module Calculator exposing (add) |
| 17 | + |
| 18 | +six = 3 + 3 |
| 19 | + |
| 20 | +add number1 number2 = number1 + number2 |
| 21 | +``` |
| 22 | + |
| 23 | +```elm |
| 24 | +-- Calculator.elm |
| 25 | +-- Define the Calculator module, and expose everything within: `six` and `add` |
| 26 | +module Calculator exposing (..) |
| 27 | + |
| 28 | +six = 3 + 3 |
| 29 | + |
| 30 | +add number1 number2 = number1 + number2 |
| 31 | +``` |
| 32 | + |
| 33 | +https://elm-lang.org/docs/syntax#modules |
| 34 | + |
| 35 | +## Importing functions from other modules |
| 36 | + |
| 37 | +Accessing functions defined in other modules is done via imports. |
| 38 | +All functions within that module that were exposed by it are made accessible when importing that module. |
| 39 | +But how they are accessed varies depending on how the module is imported. |
| 40 | + |
| 41 | +Qualified imports are the default, and accessing a function within such module (for example the `map` function in the `List` module) is done by prefixing the module name (`List.map`). |
| 42 | + |
| 43 | +Open imports enable direct access to the exposed functions within that module, without prefixing. They are done with the `exposing` keyword, like a mirror to the one used in exports. You can expose all available functions (with `..`), or specific ones (for example `map`). |
| 44 | + |
| 45 | +You can also import types, and their constructors from other modules, which is a later concept. |
| 46 | + |
| 47 | +Qualified imports are preferred to aid clarity and avoid name clashes. |
| 48 | + |
| 49 | +```elm |
| 50 | +-- qualified imports |
| 51 | +import List -- List.map, List.foldl |
| 52 | +import List as L -- L.map, L.foldl |
| 53 | + |
| 54 | +-- open imports |
| 55 | +import List exposing (..) -- map, foldl, concat, ... |
| 56 | +import List exposing ( map, foldl ) -- map, foldl, List.concat |
| 57 | +``` |
| 58 | + |
| 59 | +https://elm-lang.org/docs/syntax#modules |
| 60 | + |
| 61 | +## Type annotations |
| 62 | + |
| 63 | +Type annotations are defined with `name : parameter types -> return type`, parameter types also being separated by `->`. |
| 64 | + |
| 65 | +```elm |
| 66 | +add : Int -> Int -> Int |
| 67 | +add number1 number2 = number1 + number2 |
| 68 | +``` |
| 69 | + |
| 70 | +Parentheses can be used to define function parameters (which are themselves defined with the same syntax, hence the need for brackets). |
| 71 | + |
| 72 | +```elm |
| 73 | +-- Transform every character in a string |
| 74 | +map : (Char -> Char) -> String -> String |
| 75 | +map charMapperFunction string = |
| 76 | + -- ... |
| 77 | +``` |
| 78 | + |
| 79 | +https://elm-lang.org/docs/syntax#type-annotations |
| 80 | + |
| 81 | +## Numbers |
| 82 | + |
| 83 | +There are two types of numbers available in Elm, defined by the `Int` and `Float` types. |
| 84 | +`Int` corresponds to the set of positive and negative integers. |
| 85 | +`Float` corresponds to the set of real numbers, limited by the precision of the computer. |
| 86 | +Operations defined on numbers usually work on one type or the other, but not mixing them. |
| 87 | +There exists functions to convert between the two, such that `toFloat` which converts `Int` to `Float` and `round`, `floor`, `ceiling` or `truncate` which convert a `Float` to an `Int` with different semantics. |
| 88 | + |
| 89 | +https://package.elm-lang.org/packages/elm/core/latest/Basics#Int |
| 90 | + |
| 91 | +## String operations |
| 92 | + |
| 93 | +To describe words and sentences in code, Elm has a native `String` type. |
| 94 | +String literals are written between double quotes such as `"Hello World!"`. |
| 95 | +A string concatenation operator `++` and equality operator `==` are available by default. |
| 96 | + |
| 97 | +```elm |
| 98 | +hello : String -> String |
| 99 | +hello subject = "Hello " ++ subject |
| 100 | + |
| 101 | +hello "World!" --> "Hello World!" |
| 102 | +``` |
| 103 | + |
| 104 | +Most other string functions are in the `String` module, which needs to be imported. |
| 105 | + |
| 106 | +https://package.elm-lang.org/packages/elm/core/latest/String |
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