Language Design
Lecture 2

• What is a compiler?
• Compilers vs. interpreters
• Symbols vs. meaning

• spaces in variables (b), a says no
  • underscores instead of spaces
• latin alphabet, arabic numerals
• use emojis?
  • unicode allows this i think
• create shortcuts
  • public static void
    • #define MACRO public static void
      • use c preprocessor?
• arithmetic expressions
  • nand is enough?
  • symbols, keywords
    • or instead of ||
    • one instead 1
    • two thousand and three
  • operators
  • numbers
• functions
  • utility: reusable
  • maps a name to some copmutation, series of instructions
  • C identifiers: start character or underscore, and is a sequence of characters, underscores, digits
  • declaration: int sq; // i'm creating a new name, and i'm saying its type is an integer type
    • what if you didn't have to declare the type? infer it autoamically?
    • who cares what type it is? (some care, some don't)
      • x = 7
      • x = "jfksdlk"
      • x = x + 10
      • int f() { return 1; } f = 10;
  • sq.f = "2";
• types
  • want the language to tell us when we get types wrong

auto x;  // double
auto y;  // int 

x = 1 + 2.0;  // plus(1, 2.0)
y = 1 + 7     // plus(1, 7)


x = "string"

polymorhpism: the same symbol has different types under different contexts

language:

• c-like types, delcaration (type inference personal project)

strong definition: no untrapped errors, no invalid programs are allowed to run/compile

types: set of possible values, a set of operators on those values

• numbers, int, floating point (some limited range)
  • y = x + 1?
    • x = 2 print(y); print(y);
    • 3, 3
    • print(y) -> print(x+1); x = 10; print(x+1) -> print(10+1)
    • 3, 11
• no operators, just functions
  • recursion
  • scope?
• branching, conditionals
• while loops?
• symbols to store values, variables

paradigms:

• impertaive, recipe style
• functional

the symbol for the number one is "1"

<1> - this means the symbol 1 - this means the math notion of one (or assembly representation)

<1 + 3> => 4 // symbols 1 followed by + followed by 3, evaluates to the math number 4

• Growing a language, Guy Steele
• Null References: The Billion Dollar Mistake, Tony Hoare
• Hints on programming-language design, Tony Hoare
• Go To Statement Considered Harmful, Edsger W. Dijkstra
• Why Pascal is Not My Favorite Programming Language, Brian W. Kernighan
• C standard
• History of Programming Languages Conference (HOPL)

• Clone source code example repo (see webcourses)
• Add example programs as pull requests