Touhou Danmakufu: Functions and Subroutines

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Subroutines

Often-used codes can be shared as subroutine.

sub (name) {
    (statements)
}

In the following case,

sub fire {
    CreateShot01(GetX, GetY, 5, GetAngleToPlayer, RED01, 0);
}

fire;
fire;

is equivalent to:

CreateShot01(GetX, GetY, 5, GetAngleToPlayer, RED01, 0);
CreateShot01(GetX, GetY, 5, GetAngleToPlayer, RED01, 0);

Subroutines can be used not only to share codes but also to give names to processes. Both code-sharing and naming improve the maintainability of the program.

Functions

If the often-used codes require some parameters, or the calculational results need to be returned, functions are used instead of subroutines.

function (name) ( (parameter list) ) {
    (statements)
}

e.g. a mathematical function

f(x) = x2 + 2

is represented in Danmakufu as follows:

function f(x) {
    return x ^ 2 + 2;
}

where f is the function name, x is the parameter, and x ^ 2 + 2 is the function's value. return statement defines the function's value with parameter x. In this case, the value of f(2) is 2² + 2 = 6.

Functions can be used as subroutines. In fact, functions having no parameters and no return values are equivalent to subroutines as:

function fire {
    CreateShot01(GetX, GetY, 5, GetAngleToPlayer, RED01, 0);
}

However, functions are little bit slower than subroutines.

Functions are often used as parametrized subroutines. e.g.

function fire(v) {
    CreateShot01(GetX, GetY, v, GetAngleToPlayer, RED01, 0);
}

In this case,

fire(3);
fire(5);

is equivalent to:

CreateShot01(GetX, GetY, 3, GetAngleToPlayer, RED01, 0);
CreateShot01(GetX, GetY, 5, GetAngleToPlayer, RED01, 0);

The CreateShot01, GetX, GetY, and GetAngleToPlayer are functions, too. There are many pre-defined functions as them. For details, see Touhou Danmakufu: Functions.

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