Modeling Language: Plurals, Part 2

BH: Add a TIF in which they use a list of suffixes and expressions and then do a FOR EACH ITEM…

MF: Need to revise to follow Modeling Langauge in U1

You can improve plural to work correctly with more words. If the project is not already open, please reload it. (The suggested file name was U2-Plural.)

  1. Abstraction: Make a plural-h block that "specializes" on just one category, words that end with the letter h.
    • Start with a list of the words you want it to work for.
    • This specialist block should work correctly for words that fit its specialty plural (for words ending with h) with correct result for the word crutch suffix s (for words ending in h) with result for moth, plural (for words ending in h) with result. It can be completely wrong about words that don't fit its specialty plural (for words ending with h) with wrong result for mouse (wrong input) because the plural block should never give words to plural-h unless those words end with h.
    • Test plural-h with a variety of words to make sure it works the way you want. Then use map to test it on the entire list you made earlier.

    2. Abstraction: Language often has special cases. In English, the plurals ofsome nouns add s; some add es; nouns like calf and fly become calves and flies, changing their final letters before adding es. And more. For a programming task this complex, it's (generally) best to break it into parts, handle each part separately with its own procedure (its own block), and then have the "top-level" block—in this case, plural, itself—use those specialists. That is, instead of coding every little detail directly in plural, it is cleaner and clearer to make plural look something like this.

    abstract definition of plural: if h = last letter of word, report h-case plural; if y = last letter of word, report y-case plural; if some other case, use a block that specializes in that case; etc.; else report join word s

    Showing the structure of the method—just the overall strategy—in the "top-level" block and leaving the details to separate blocks is one part of an important computer science idea called abstraction. Abstraction keeps your code clear, readable, and more easily debugged. It will also help your code be more flexible.

  2. When you trust your new specialist block, edit plural to use the specialist. Test (you can use map) to make sure plural still works for all the words it used to work for, as well as the new ones.
  3. Create plural-y to handle words like plural_y-tray-with-result and plural_y-sky-with-result

    4. Remember, any specialist can make mistakes if it's asked to do a job that isn't its specialty. plural_y-mouse-with-(wrong)result

    Make sure plural gives it only the job it knows how to handle correctly.

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I'm not thrilled with the way this pushes a particular implementation for a reason that's hidden until they get there, and doesn't make sense on its own. bh
  1. Because you know what keep-items-such-that-(last-letter-of-(input)-equals-h)-from-test-list does, you can, if you like, use just that specialized list as input to a test of plural or plural-h, this way.map-plural(with-input)-over-(keep-items-such-that-(last-letter-of-(input)-equals-h)-from-test-list)
  2. Extend plural to handle another special case. Use a special-purpose block for your special case to keep plural from becoming cluttered.
  3. Right now, if plural is given a word with a space at the end, it leaves that space in the plural, like this: plural of bulldog with space at the end, and result with space before s. Figure out how to handle this special case and edit plural so that the result is plural of bulldog with space at the end, and correct result, no space before s. You already have a block that specializes in making plurals of words that don't have a space at the end. Use it.
  4. Surprise! Once plural works for a single space at the end of a word, try giving it plural of bulldog with four spaces at the end. That works!! But why?!
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