kogupta / craftinterpreter

Working through the delightful "Crafting Interpreters" book

Crafting interpreters

Working through the delightful book.

Chapter 4

• use switch statements with disjoint branches to break free from myriad breaks

    case '(' -> addToken(LEFT_PAREN);
    case ')' -> addToken(RIGHT_PAREN);
    // ...
    case ' ', '\r', '\t' -> {}       // whitespace
    case '\n' -> line++;             // line ending
    // ...
    default -> { ... }

• logically, scanner can be thought of as Source => Stream[Token]

  

• "contiguous" errors can be batched as follows:

  • model errors as: record ScanError(int line, int start, int end, String message)
  • accumulate errors in JDK ArrayList
  • merge current error with last error if they are consecutive characters
  • since errors are appended to this list, insert/delete of last error is very cheap (an array access)

Chapter 5

• sealed traits and pattern matching y'all

• breakfast grammar:

  breakfast  -> protein "with" breakfast "on the side" ;
  breakfast  -> protein ;                => protein ("with" breakfast "on the side")? | bread
  breakfast  -> bread ;
             
  protein    -> crispiness "crispy" "bacon" ;
  protein    -> "sausage" ;
  protein    -> cooked "eggs" ;          => ("scrambled" | "poached" | "fried" ) "eggs" ;
             
  crispiness -> "really" ;
  crispiness -> "really" crispiness ;    =>  crispiness -> "really"+ ;
             
  cooked     -> "scrambled" ;
  cooked     -> "poached" ;              => cooked -> "scrambled" | "poached" | "fried" ;
  cooked     -> "fried" ;
             
  bread      -> "toast" ;
  bread      -> "biscuits" ;             => bread -> "toast" | "biscuits" | "English muffin";
  bread      -> "English muffin" ;
  

  in regex terms become:

  breakfast -> protein ( "with" breakfast "on the side" )? | bread ;
  protein   -> "really"+ "crispy" "bacon" | "sausage" | ( "scrambled" | "poached" | "fried" ) "eggs" ;
  bread     -> "toast" | "biscuits" | "English muffin" ;
  

• lox init grammar:

  expression  ->  literal
               | unary
               | binary
               | grouping ;
  literal     -> NUMBER | STRING | "true" | "false" | "nil" ;
  grouping    -> "(" expression ")" ;
  unary       -> ( "-" | "!" ) expression ;
  binary      -> expression operator expression ;
  operator    -> "==" | "!=" | "<" | "<=" | ">" | ">=" | "+"  | "-"  | "*" | "/" ;
  

• operators:

  symbol	repetition
  *	0 or more
  +	at least once - 1 or more
  ?	at most once - 0 or 1