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Midterm Review

CS 242. Midterm Review. TA Help Session. Midterm Exam Wednesday Oct 26 7:00 – 9:00 PM Gates B01. Today’s Outline. Brief Introduction/Review of course so far Review final slides ~10-15 mins Help stimulate useful questions Office Hours on steroids

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Midterm Review

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  1. CS 242 Midterm Review TA Help Session Midterm Exam Wednesday Oct 26 7:00 – 9:00 PM Gates B01

  2. Today’s Outline • Brief Introduction/Review of course so far • Review final slides • ~10-15 mins • Help stimulate useful questions • Office Hours on steroids • All of the TA’s will be available to answer questions • Note: No section Friday

  3. Summary of the course • Lisp • Computability • Fundamentals • lambda calculus • functional prog • ML and type systems • Block structure and activation records • Exceptions • Scripting Lang/DSL’s

  4. Lisp Summary • Successful language • Symbolic computation, experimental programming • Specific language ideas • Expression-oriented: functions and recursion • Lists as basic data structures • Programs as data, with universal function eval • Stack implementation of recursion via "public pushdown list" • Idea of garbage collection.

  5. Fundamentals • Grammars, parsing • Lambda calculus • Functional vs. Imperative Programming • Is implicit parallelism a good idea? • Is implicit anything a good idea?

  6. Algol Family and ML • Evolution of Algol family • Recursive functions and parameter passing • Evolution of types and data structuring • ML: Combination of Lisp and Algol-like features • Expression-oriented • Higher-order functions • Garbage collection • Abstract data types • Module system • Exceptions

  7. Types and Type Checking • Types are important in modern languages • Program organization and documentation • Prevent program errors • Provide important information to compiler • Type inference • Determine best type for an expression, based on known information about symbols in the expression • Polymorphism • Single algorithm (function) can have many types • Overloading • Symbol with multiple meanings, resolved at compile time

  8. Block structure and storage mgmt • Block-structured languages and stack storage • In-line Blocks • activation records • storage for local, global variables • First-order functions • parameter passing • tail recursion and iteration • Higher-order functions • deviations from stack discipline • language expressiveness => implementation complexity

  9. Summary of scope issues • Block-structured lang uses stack of activ records • Activation records contain parameters, local vars, … • Also pointers to enclosing scope • Several different parameter passing mechanisms • Tail calls may be optimized • Function parameters/results require closures • Closure environment pointer used on function call • Stack deallocation may fail if function returned from call • Closures not needed if functions not in nested blocks

  10. Control • Structured Programming • Go to considered harmful • Exceptions • “structured” jumps that may return a value • dynamic scoping of exception handler • Continuations • Function representing the rest of the program • Generalized form of tail recursion

  11. Scripting Language Upsides • Optimize for people, not machines • Principle of Least Surprise (after you know the language well…) • There’s more than one way to do it (TMTOWTDI, pronounced Tim Toady) • No built-in limits • Make common things short • Make easy tasks easy and hard tasks possible • Executable pseudo-code

  12. Scripting Language downsides… • “Write once, read never” • Perl in particular seems to facilitate writing difficult to read programs. A consequence of TMTOWDI? • Performance can be difficult to predict • Fast: regular expression processing • Slow: threads • Shell calls? • Errors are detected dynamically

  13. Domain Specific Langs Summary • All languages have a domain. • Languages provide a rich interface to computers. • Tailored abstractions are powerful: • support domain experts • make code more reliable (shorter: boring code is generated) • Less is more • Extra reasoning principles & more optimization opportunities • Two for one specials • Executable, verification support, auxiliary tools, … • Languages are constantly being designed, implemented, and used.

  14. Questions? • Remember: Midterm Exam • Wednesday Oct 26 (Tonight) • 7:00 – 9:00 PM • Gates B01 (this room) • Closed Book, Closed Notes

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