gistfile1.txt

        Generates bytecode for if expression.

        To understand how it works consider the
        following Scheme code:

        (if (> 3 8) 10 14)

        Results in the following bytecode:
        array('i', [9, 0, 9, 1, 5, 6, 1, 2, 17, 14, 9, 2, 16, 16, 9, 3])
        
        and disasm run outputs the following:
        
        literals:
        0: 3
        1: 8
        2: 14
        3: 10

        instructions:
        --------------------------------------------------
        0000         push_literal literal=0
        0002         push_literal literal=1
        0004           push_local idx: 6, name: >
        0006                 call argc=2
        0008    goto_if_not_false ip=0x000E
        000A         push_literal literal=2
        000C                 goto ip=0x0010
        000E         push_literal literal=3
        0010         ...

        If expression in this example has condition expression,
        "then" clause and "else" clause. It is turned into two
        jump instructions and three
        instructions (or sequences instructions in more complex
        cases), one for condition expression,
        one for "then" clause and one for "else" clause.

        In the example above condition expression is (> 3 8) which
        results into instructions

        0000         push_literal literal=0
        0002         push_literal literal=1
        0004           push_local idx: 6, name: >
        0006                 call argc=2

        Then goto_if_not_false instruction is used to jump to "then"
        clause if value on top of the stack (result of evaluating
        of 

        0008    goto_if_not_false ip=0x000E

        jumps to instruction at 0x000E if value on top of the stack
        is not false.

        0x000E is the value of "then" clause that pushes 10 on top
        of the stack in this example:

        000E         push_literal literal=3

        10 comes from 3rd literal in literals frame.

        if jump at 0008 did not happen, instruction at
        000A is executed:

        000A         push_literal literal=2

        it pushes 14 (2nd slot in literals frame) onto the stack.
        14 is the value of "else" clause in this example. Then
        to jump over "then" clause we use goto instruction.