Function blocks and scoped variables

This version of gnuplot introduces a mechanism for invoking a block of standard gnuplot commands as a callable function. A function block can accept from 0 to 9 parameters and returns a value. Function blocks can be used to calculate and assign a new value to a variable, to combine with other functions and operators, or to perform a repetitive task preparing data. There are three components to this mechanism. See local, scope, function blocks, return.

• The local qualifier allows optional declaration of a variable or array whose scope is limited to the duration of execution of the program unit in which it is found. These units currently include execution of a load or call statement, function block evaluation, and the code block in curly brackets following an if, else, do for, or while statement. If the name of a local variable duplicates the name of a global variable, the global variable is shadowed until exit from the local scope.
• The function command declares a named function block (effectively an array of strings) containing gnuplot commands. When the function block is invoked, commands are executed successively until the end of the block or until a return command is encountered.
• The return <expression> command terminates execution of a function block. The result of evaluating <expression> is returned as the value of the function. Anywhere outside a function block return acts like exit.

Please see function_block.dem for an example of using this mechanism to define and plot a non-trivial function that is too complicated for a simple one-line definition f(x) = ....