Functions

Functions are essential to any language. They allow us to reuse code and solve complex problems.

Defining Functions

Defining a named function is similar to naming any other value in Grain.

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let add = (x, y) => x + y

A function can perform a series of actions. One thing to note about functions in Grain is that they always return the result of the final expression in the function body, without needing an explicit return statement.

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let logAndAdd = (x, y) => {
  print(x)
  print(y)
  x + y
}

Functions as First Class Citizens

Since functions are just like any other values in Grain, they can be passed as arguments to other functions.

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let doMath = (fn, x, y) => fn(x, y)

let multiply = (x, y) => x * y
let subtract = (x, y) => x - y

doMath(multiply, 4, 6) // 24

Multiple Return Values

You can return multiple values from functions using tuples.

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let translateCoordinates = (x, y) => {
  (x + 4, y + 4)
}

let (x, y) = translateCoordinates(1, 2)
print(x) // 5
print(y) // 6

Recursive Functions

We can define recursive functions using the rec keyword. Recursive functions are a key part of Grain, so remember to use let rec when necessary!

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let rec fibonacci = (n) => {
  if (n == 0 || n == 1) {
    n
  } else {
    fibonacci(n - 1) + fibonacci(n - 2)
  }
}