This, the first graded assignment of the semester asks you to solve a simple problem in each of five different programming languages (six if you’re in 454):
The problem is Exercise 6.23 in the textbook:
Construct a program that outputs (in some order) all structurally distinct binary trees of n nodes. Two trees are considered structurally distinct if they have different numbers of nodes or if their left or right subtrees are structurally distinct. There are, for example, 5 structurally distinct trees of 3 nodes:
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These are most easily output in “dotted parenthesized form”:
(((.).).) ((.(.)).) ((.).(.)) (.((.).)) (.(.(.)))
You can think of the parenthesized expressions as being generated by the following simple grammar:
T →
a tree can be empty T → (T.T)
or a node with left & right children
Finding trees is a naturally recursive problem (iterative solutions are
also possible). The easiest and most elegant
solutions employ a recursive set of iterators, which are
abstractions used to drive
a for
loop. We will study iterators in
Section 6.5.3; you
may want to read ahead. In the terminology of that section,
you’ll find that Python and C# have “true”
iterators.
Prolog’s search mechanism can be used to create the equivalent of
iterators, and yields a very elegant solution.
Ada and Scheme have no special iterator support; for these you’ll have to
work with lists (or find some other solution—e.g., tasks in
Ada).
For what it’s worth, Java and C++ (which you can try for extra credit)
have iterator objects, which are sort of half of what you
want.
If you already knew all the languages, you’d probably find your task easiest in Prolog and hardest in Ada, with the other languages ranging in between. (Of course you probably don’t know all the languages already, so the unfamiliar ones will be the hardest.) A hint: the companion site for the fourth edition of the textbook contains working versions of all the nontrivial examples in the book. For Ada and C# you might find it helpful to start with one of these: it will already import appropriate libraries and contain examples of the control constructs, I/O calls, etc.
When run, your programs should read a single integer n from
standard input; most should then print the appropriate trees to
standard output (as dotted lists, one per line, in arbitrary order).
For Prolog, which runs in an interpreter, please arrange for
trees(n, L)
to produce successive trees (values for
L
) in response to a semicolon prompt. For Scheme,
please arrange for (trees n)
to evaluate to a list of
trees, each of which is a (nested) list.
You may work alone on this project or in teams of two. If you split up
the languages, whoever takes Ada should probably do two; the other
person should do three.
However you divide the programming,
each team member must write his or her own
README
file (no sharing of text on this allowed), and turn in
the project separately (with all five or six programs, which
will be the same as the partner’s code).
This means, of course, that you’ll need to really
understand your partner’s code.
Be sure to read the instructions on the
grading page regarding the turn-in
procedure and requirements.
To turn in your code, use the following procedure, which will be the
same for all assignments this semester:
On a csug
machine,
put your write-up in a README.txt
, README.md
, or
README.pdf
file in the same directory as your code, and
(while still in that directory) run
the script ~cs254/bin/TURN_IN
.
The script will package the contents of the directory (and any
subdirectories) into a bundle and send it to the TAs for grading (so
clean up any mess you might have in the directory first).
Be sure your write-up (README
file) describes any features
of your code that the TAs might not immediately notice. In
addition, for this assignment, your
README
file must compare and contrast the
programming experience in the different languages you used (all five/six
of them). What was easy? What was hard?
Are there noticeable differences in speed?
What do you like/dislike?
Did you find iterators to be helpful?
We will be using the following language implementations.
The Ruby, Python, and Prolog interpreters, the Haskell interpreter and
compiler, the Ada and Rust compilers, and the OCaml interpreter and
compiler are found in /usr/bin
.
The Scheme interpreter is found in /usr/staff/bin
.
The remaining implementations (for C#, Go, and Swift)
are in /u/cs254/bin
, which you
should append to your PATH
environment variable (ask a
friend or one of the TAs if you
don’t know how).
gnatmake
(a wrapper for the
GNU Ada translator). It produces native executables.
mcs
(the Mono project C#
compiler) and run with the mono
JIT/run-time system.
go
.
ghci
interpreter, or
compile with ghc
(the Glasgow Haskell Compiler) to
produce native binaries.
swipl
interpreter.
python3
interpreter.
ocaml
interpreter, or
compile with ocamlc
to produce native binaries.
ruby
interpreter.
rustc
.
plt-r5rs
or, under X, with the drracket
GUI.
Be sure to configure the latter to use the R5RS language standard
(it boots up expecting a vastly expanded language that will try to
force you to use modules and other features you don’t want to
have to learn at this point.)
swift
interpreter, or
compile with swiftc
.
You are welcome to work with other language implementations and/or platforms, but you must ensure that your final versions compile and run correctly using the implementations listed above. We will be testing using only these.
I won’t be devoting lecture time to how to use these languages. You’ll need to find on-line tutorials or other resources, and teach yourself. Here are some decent starting points:
README
.
Before the end of the day on Sunday, January 26, complete the T1 trivia assignment found on Blackboard.