Function-Related Formatting Rules

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§4 Function Definition

§4.1 Function Signature. No space between the function name and the parameter list.

// ✅ Correct
foo: (a: Int, b: Int) -> Int = a + b

// ❌ Incorrect
foo : (a: Int, b: Int) -> Int = a + b

§4.2 Parameter List Line Break. When the parameter list exceeds the line width, each parameter occupies one line, with a trailing comma.

// Exceeds line width
very_long_function_name: (first_param: Int, second_param: Int, third_param: Int) -> Int = first_param + second_param + third_param

// After formatting
very_long_function_name:
    first_param: Int,
    second_param: Int,
    third_param: Int,
) -> Int = first_param + second_param + third_param

§4.3 Return Type. The return type is connected to the parameter list with ->, with one space before and after ->.

// ✅ Correct
foo: () -> Int = 1

// ❌ Incorrect
foo: () ->Int = 1
foo: ()-> Int = 1
foo:()-> Int = 1

§4.4 Function Body. The function body is separated from the return type by a single space.

// ✅ Correct
foo: () -> Int = 1

// ❌ Incorrect (two spaces)
foo: () -> Int  = 1

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§7 Function Call

§7.1 Parameter List. Parameters are separated by commas, with one space after each comma.

// ✅ Correct
foo(1, 2, 3)

// ❌ Incorrect
foo(1,2,3)
foo(1 , 2 , 3)

§7.2 Named Arguments. Named arguments use the name = value format.

// ✅ Correct
foo(x = 1, y = 2)

// ❌ Incorrect
foo(x=1, y=2)

§7.3 Parameter Line Break. When the argument list exceeds the line width, each argument occupies one line, with a trailing comma.

// Exceeds line width
very_long_function_name(first_argument, second_argument, third_argument)

// After formatting
very_long_function_name(
    first_argument,
    second_argument,
    third_argument,
)

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§12 Lambda Expressions

§12.1 Lambda Format. Lambda uses the (params) => body format.

// ✅ Correct
f = (x) => x + 1

// Single expression body
f = (x) => x * 2

// Multi-statement body
f = (x) => {
    y = x + 1
    y * 2
}