CS 3723 Programming Languages

Assignments:

• Grammar Homework
• II. Initial Parser
• III. Translate AEs to Quadruples
• IV. Translate Control Structures

Topics:

• Parsers:
  • Construction of top-down recursive descent parsers (the main technique we used in the course).
  • Construction of a bottom-up parser (using ``weak precedence'' and a simple grammar for arithmetic expressions). Illustration of how this parser works using a parse stack.
• Translation of AEs to Quadruples (Project III):
  • Use of temporary locations.
  • Each function of the parser returns an integer. This integer gives the location of a variable that will hold, at run time, the value of the construct recognized by the function.
• Translation of Control Structures to Quadruples (Project IV):
  • Translating gotos.
  • Backpatching quadruples.
  • Translating relational expressions.
  • Translating if-else and while-do constructs (both involving backpatching).
• Implementing functions and parameters:
  • Need extensions of the Quadruple machine, at least to include and indirect JMP.
  • Use of a run-time stack of return points to support function call/return including recursive functions.
  • Use of a run-time stack and activation records to support return addresses, parameters to functions, local variables, local arrays, value returned by a function, and pointers of various kinds.
• Run-time storage management:
  • The Burroughs machine used a hardware stack, which turns out to be a poor allocation of hardware resources.
  • Constrast C, C++, and Java with respect to:
    simple variables, arrays, structs (or classes, parameters, return values, assignment operator, static variables, dynamic allocation, dynamically allocating primitive types (C/C++ yes, Java no except in type-wrapper classes), allocating arrays, automatic initialization, recovering dynamic storage (C uses free, C++ uses new, Java automatic with garbage collection).
  • Static and global variables declared in a separate area.
  • Local variables on the stack.
  • New (or malloced) objects in a separate area (called the heap).
• Postscript:
  • A 2-dimensional page description language.
  • Allows the font characters themselves to be described algorithmically and manipulated.
  • Provides many good primitives for drawing 2-dim figures.
  • Postscript Programs
• Prolog:
  • Get rid of: gotos, pointers, assignments, functions.
  • Prolog is logic-based. Like SQL, we say what we want without saying how to achieve the desired result.
  • Prolog knowledgebase example
  • Example Prolog session
  • Other Prolog examples
  • Prolog Manual
    (Follow the link and click on the upper left "contents" icon.)

Sample Questions:

• About parsers:
  • Given a parser, say what it is doing (and how).
  • Write a parser for a simple example language.
• Translating AEs to quads:
  • Explain how the returned addresses of run-time variables work. (Variables which will hold the desired value at run time.)
  • Given some semantic actions, say how they are working.
  • Given a parser, create semantic actions to do some simple task.
• Translating control stuctures:
  • Describe how the backpatching works.
  • Actually do the translation for some simple example.
• Functions and parameters:
  • Show the activation records used at run-time on a stack. Explain.
• Run-time storage management:
  • Explain how and when the run-time stack is used.
  • Explain about the heap, including garbage collection.
• Postscript:
  • Given a simple example program, answer questions about it.
• Prolog:
  • Given a simple example program, answer questions about it.