Guido van Robot Language Reference

The Five Primitive Guido van Robot Instructions:

    move
    turnleft
    pickbeeper
    putbeeper
    turnoff

Block Structuring

Each Guido van Robot instruction must be on a separate line. A sequence of one or more Guido van Robot instructions that are all indented the same number of spaces compose a block of code. <instruction> refers to any of the five primitive instructions above, the conditional branching or iteration instructions below, or a user defined instruction.

    <instruction>
    <instruction>
      ...
    <instruction>

Conditional Branching

Conditional branching refers to the ability of a program to alter it's flow of execution based on the result of the evaluation of a conditional. The three types of conditional branching instructions in Guido van Robot are if and if/else and if/elif/else. <test> refers to one of the eighteen conditionals below.

    if <test>:
        <block>

    if <test>:
        <block>
    else:
        <block>

    if <test>:
        <block>
    elif <test>:
        <block>
    ...
    elif <test>:
        <block>
    else:
        <block>

Conditionals

GvR has eighteen built-in tests that are divided into three groups: the first six are wall tests, the next four are beeper tests, and the last eight are compass tests:

    front_is_clear
    front_is_blocked
    left_is_clear
    left_is_blocked
    right_is_clear
    right_is_blocked

    next_to_a_beeper
    not_next_to_a_beeper
    any_beepers_in_beeper_bag
    no_beepers_in_beeper_bag

    facing_north
    not_facing_north
    facing_south
    not_facing_south
    facing_east
    not_facing_east
    facing_west
    not_facing_west

Iteration

Iteration refers to the ability of a program to repeate an instruction (or block of instructions) over and over until some condition is met. The two types of iteration instructions are the do and while instructions. <positive_number> must be an integer greater than 0.

    do <positive_number>:
        <block>

    while <test>:
        <block>

Defining a New Instruction:

New instructions can be created for Guido van Robot using the define statement. <new_name> can be any sequence of letters or digits as long as it begins with a letter and is not already used as an instruction. Letters for Guido van Robot are A..Z, a..z, and the underscore (_) character. Guido van Robot is case sensitive, so TurnRight, turnright, and turnRight are all different names.

    define <new_name>:
        <block>

Simplest GvR Program

Execution of a GvR program ends with the turnoff instruction. Any program which reaches the end of its instruction sequence without encountering turnoff is considered in error. Thus the simplest GvR program is:

    turnoff

An Example Program

Given the following world:

rightWall world

The following program will make Guido follow the right wall until he encouters a beeper:

    define turnright:
        do 3:
            turnleft

    define follow_right_wall:
        if right_is_clear:
            turnright
            move
        elif front_is_clear:
            move
        else:
            turnleft

    while not_next_to_a_beeper:
        follow_right_wall

    turnoff