Difference between revisions of "CS422 - Programming Language Design (Spring 2020)"

Exercise 1 (10 points): Modify IMP (its Big-Step and its Small-Step SOS) to halt when a division-by-zero takes place, returning a configuration holding the state in which the division by zero took place.

Exercise 2 (10 points): Add a variable increment construct, ++x (increment x and return the incremented value), to IMP: first add it to the formal BNF syntax, then to the Big-Step SOS, then to the type-system, and then to the Small-Step SOS.

Exercise 3 (10 points): Add I/O constructs, read() and print(AExp) to IMP: first add these to the formal BNF syntax (read() is an AExp construct and print(AExp) is a Stmt construct), then to the Big-Step SOS, then to the type-system, and then to the Small-Step SOS.

Exercise 4 (10 points): Combine the three above: add division-by-zero halting, an increment construct, and the two I/O constructs to IMP. Feel free to comment on what's going on, particularly on how inconvenient it is to do certain things in SOS (one of the points of this HW is to understand the limitations of SOS, so you will appreciate K).

Exercise 1 (10 points): The current K LAMBDA semantics of mu (in Lesson 8) is based on substitution, and then letrec is defined as a derived operation using mu. Give mu a different semantics, as a derived construct by translation into other LAMBDA constructs, like we defined letrec in Lesson 7. To test it, use the same definition of letrec in terms of mu (from Lesson 8) and write 3 recursive programs, like the provided factorial-letrec.lambda.

Note: See the mu-derived exercise in the nightly built for details and test programs.

Exercise 2 (10 points): Modify the K definition of IMP to not automatically initialize variables to 0. Instead, declared variables should stay uninitialized until assigned a value, and the execution should get stuck when an uninitialized variable is looked up.

Note: See the uninitialized-variables exercise in the nightly built for details and test programs.

Exercise 3 (10 points): Mofify IMP so that the K "followed by" arrow, ~>, does not explicitly occur in the definition (it currently occurs in the semantics of sequential composition). Hint: make sequential composition strict(1) or seqstrict, and have statements reduce to "{}" instead of ".", ... and don't forget to make "{}" a KResult (you may need a new syntactic category for that, which only includes "{}" and is included in KResult).

Note: See the purely-syntactic exercise in the nightly built for details and test programs.

Exercise 4 (10 points): Define a variant of callcc, say callCC, which never returns to the current continuation unless a value is specifically passed to that continuation. Can you define them in terms of each other? Do these in both the substitution and the environment-based definitions.

Note: See the callCC (substitution), from-call-CC-to-callcc (substitution), from-callcc-to-call-CC(substitution), callCC (environment), from-call-CC-to-callcc (environment), and from-callcc-to-call-CC (environment) exercises in the nightly built for details and test programs.