Yet another Rust implementation for Crafting Interpreter's tree walk interpreter for Lox language.
Note: Precedence for optional implementations
(extra materials from the book) roughly follows C's (not C++) grammar,
with one difference: I'm not sure how to restrict assignments's left hand side
to equality instead of ternary in a recursive descent parser.
See StackOverflow and The Syntax of C in Backus-Naur form.
program ::= declaration* EOF
declaration ::= varDecl | statement
varDecl ::= "var" IDENTIFIER ( "=" expression )? ";"
statement ::= exprStmt | ifStmt | printStmt | whileStmt | block
ifStmt ::= "if" "(" expression ")" statement ( "else" statement )?
whileStmt ::= "while" "(" expression ")" statement
forStmt ::= "for" "(" varDecl | exprStmt ";" expression? ";" expression? ")" statement
block ::= "{" declaration* "}"
exprStmt ::= expression
printStmt ::= "print" expression
expression ::= comma
comma ::= assignment ( "," assignment )*
assignment ::= ternary "=" assignment | ternary
ternary ::= logic_or "?" expression ":" ternary
logic_or ::= logic_and ( "or" logic_and )*
logic_and ::= equality ( "and" equality )*
equality ::= comparison ( ( "!=" | "==" ) comparison )*
comparison ::= term ( ( ">" | ">=" | "<" | "<=" ) term )*
term ::= factor ( ( "-" | "+" ) factor )*
factor ::= unary ( ( "/" | "*" ) unary )*
unary ::= ( "!" | "-" ) unary | primary
primary ::= NUMBER | STRING | "true" | "false" | "nil" | "(" expression ")" | IDENTIFIER