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### 5.4 Function Definitions

A command or function definition consists in a header followed by a block of instructions delimited by `end`.

A command definition header consists in a command name followed by a comma separated parameter declaration list enclosed in parenthesis. A parameter declaration consists in a parameter type: `number`, `point`, `vector`, `set`, `line`, `circle`, `conic` or `string`, followed by a parameter name. A function definition header is identical to a command definition header except that it starts with a return type.

A function definition must contain at least a return statement, which consists in the `return` keyword followed by an appropriate expression. Command definitions may contain empty return statements.

Example:

    number square(number x)
      return x*x
    end

Variables may be declared local to a command or function definition using the `local` keyword.

Example:

    vector conjugate(vector v)
      local x, y
      x = abscissa(v)
      y = ordinate(v)
      return vector(x, -y)
    end