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. Functions in Grain always return the result of the final expression in the function body.

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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) {
    1
  } else {
    fibonacci(n - 1) + fibonacci(n - 2)
  }
}