The Style

In addition to following the design recipe, all code must adhere to the following basic style guidelines:

  1. Start every file with a standard header:

    ; Authors: <directoryID1>, <directoryID2>
    ; Purpose: <concise, high-level purpose statement for program>

    These should be the first two lines of the file.

  2. Organize your program top-down, regardless of how you actually work through your wish list. The phrase "top down" means that project files consist of a general purpose statement, a data definition and a constant definition section, a main function, followed by sections for handler functions, and wrapped up by general utility functions.

    The main function is the one that uses big-bang, read-file, write-file, and so on. A good purpose statememt for the main function explains how to use it. For example,

    ; PortNumber -> ClientState
    ; (client p) connects to port p on
    ; the SERVER machine, deals with incoming messages, displays
    ; ...
    ; Try with (client 10002)
    (define (client port-no)
      (big-bang CLIENTSTATE0
        [register SERVER]
        [port     port-no]
        [to-draw render-client-state]))

    Note the specific sample function call.

    Separate distinct sections of your program with dashed lines that are exactly 80 columns wide.

  3. Arrange your functions according to the design recipe. Place short and informative test cases between the signature and the function definition. Place any additional long or complicated test cases below the function or at the bottom of your program in a separate test section.

  4. Use (function, constant, parameter) names that make sense with respect to the problem.

  5. Design concise functions. No function should span more than five to eight lines. If it does, reconsider your interpretation of the "one task, one function" guideline.

    If a function consumes a complex argument and must perform several different tasks, design several functions that all consume the argument, produce a value in the same data collection, and hand it over to the next function:

    ;; ------------------------------------------------- GOOD

    ;; HHState -> HHState


    (define (hungry-henry-action-per-clock-tick hh-world-state)



           (move-hungry-henry-closer-to-wp hh-world-state))))


    ;; HHState -> HHState

    (define (bump-tick-value hh-world-state) ...)


    ;; HHState -> HHState

    (define (eat-all-cup-cakes-in-reach hh-world-state) ...)


    ;; HHState -> HHState

    (define (move-hungry-henry-closer-to-wp hh-world-state) ...)

    Piling the code from these three functions into the first one would yield a confusing mess.

  6. Keep lines narrow. No line should span more than 80 characters. See bottom right of DrRacket or use its edit -> find longest line menu.

    Break lines at those points suggested by HtDP.

  7. Use proper indentation. Use the indentation style of DrRacket in your program. To indent a selected portion of your file, press tab. Ctrl+A is useful to select all of the file.

  8. Programs use the parentheses style displayed in HtDP and this web page:

    ;; ------------------------ GOOD

    (define (f l)

      (cond [(empty? l) 0]

            [else (f (rest l))]))


    ;; ------------------------ BAD

    (define (f l)

      (cond [(empty? 1) 0]

            [else (f (rest l))]



    The dangling parentheses in the second code excerpt are considered extremely bad style. You will lose all style points for using it even once.

Not observing these very basic guidelines leads to unreadable code and to loss of points.