CSC362.01, Class 2: An Abbreviated Introduction to Pascal

Admin:
* Surprize: No Quiz
* Attendance is required
* Almost everything I type on the screen gets recorded in an EBoard, available through the current outline or the EBoards link
* How did you feel about lab 1?
  * Lack some fundamental skills, e.g., Unix terminal windows, Assembly, 
  * You should mail me your results (day or so), but I do not grade them
  * Open-endedness
* Read chapter 1 of ASU.

Overview:
* A short history of Pascal
* Reflection: What are they key building blocks of an imperative language?
* [To be filled in]

Detour: Question four from lab 1

Good compiler design says
* One intermediate language
* Compile high-level language to intermediate
* Compile intermediate to various targets
         pascal        68K
                 \   /
              c - INT - i86
                 /   \
          fubula        mips
* In this class, I said "GNU trees"
* On the eboard, I said "RTL"
* 

About Pascal
* Until the late 1950's, there were no high-level languages
* First patch cords
* Then "virtual patch cords" that employed the von Neumann principle
* Then assembly
* Four initial "threads" of programming langauge design
  * Fortran: Scientific Computation / Number crunching
  * COBOL: Business Computation / Information processing
  * LISP: AI computation / Simultating knowledge
  * Algol: Communicate algorithmic ideas
* Nicklaus Wirth
  * Simplify
  * Keep key constructs
  * Never trust the programmer
  * Good for students
  * Support structured programming

What aspects of an imperative language would you expect to learn?
* Types (note that Wirth thought many errors were type based)
* Control structures
  * Loops
  * Conditionals
  * Sequencing
  * Procedure/Function/Subroutine
  * Goto considered harmful
* Key operators (+ , -, *, /, etc.)
* Basic statements
  * Assignment
  * Input
  * Output
* Overall program structure
* Variables

program NAME(LIST-OF-PORTS);
CONSTANT-DECLARATIONS
TYPE-DECLARATIONS
VARIABLE-DECLARATIONS
PROCEDURE-AND-FUNCTION-DECLARATIONS
begin
  LIST-OF-STATEMENTS
end.

VARIABLE-DECLARATIONS
  var
    NAME1,NAME2,....NAMEn: TYPE;
    NM1,NM2,...NMm: TYPE;

ASSIGNMENT STATEMENTS

  NAME := EXP;

INPUT

  read(VAR);
  readln(VAR);

OUTPUT

  write(EXP);
  writeln(EXP);

In C, semicolons *terminate* statements, In Pascal, semicolons *separate* statements

CONDITIONAL

  if TEST then
    STATEMENT

  if TEST then
    STATEMENT
  else
    STATEMENT

if TEST1 then if TEST2 then STATEMENT1 else STATEMENT2

if (test1) if (test2) statement1; else statement2;

if (itsFriday) {
  if (its115) {
    go to Sam's class
  }
  else {
    sleep
  }
}

if (itsFriday) {
  if (its115) {
    go to Sam's class;
  }
}
else {
  sleep;
}

Case Statement

case (EXP) of
  VAL: STATEMENT;
  VAL: STATEMENT;
  ...
  VAL: STATEMENT
end

We need a "default" or "else"
It's nicer to have more than one thing on the left

	VAL1,VAL2: STATEMENT

Inclusive ranges are nice

	VAL1..VAL2: STATEMENT

Combinations are nice
	1..3, 5, 7..11: STATEMENT

Compound statement

	begin
	  STATEMENT;
	  STATEMENT
	end
Who cares about complete coverage?