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require_relative "error"
require_relative "expr"
require_relative "stmt"
module Lox
class Parser
def initialize(tokens)
@tokens = tokens
@current = 0
end
def parse!
statements = []
until eot?
statements << declaration
end
statements
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rescue ParseError => e
$stderr.puts e.message
synchronize!
end
private
def declaration
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return class_decl if match?(:CLASS)
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return function("function") if match?(:FUN)
return var_declaration if match?(:VAR)
statement
end
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def class_decl
name = consume!(:IDENTIFIER, "Expect class name.")
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superclass = if match?(:LESS)
consume!(:IDENTIFIER, "Expect superclass name.")
Expr::Variable.new(prev)
else
nil
end
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consume!(:LEFT_BRACE, "Expect '{' before class body.")
methods = []
until check?(:RIGHT_BRACE) || eot?
methods << function("method")
end
consume!(:RIGHT_BRACE, "Expect '}' after class body.")
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Stmt::Class.new(name, superclass, methods)
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end
def var_declaration
name = consume!(:IDENTIFIER, "Expect variable name.")
initializer = match?(:EQUAL) ? expression : nil
consume!(:SEMICOLON, "Expect ';' after variable declaration.")
Stmt::Var.new(name, initializer)
end
def while_stmt
consume!(:LEFT_PAREN, "Expect '(' after 'if'.")
cond = expression
consume!(:RIGHT_PAREN, "Expect ')' after 'if'.")
body = statement
Stmt::While.new(cond, body)
end
def statement
return for_stmt if match?(:FOR)
return if_stmt if match?(:IF)
return print if match?(:PRINT)
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return return_stmt if match?(:RETURN)
return while_stmt if match?(:WHILE)
return Stmt::Block.new(block) if match?(:LEFT_BRACE)
expression_stmt
end
def for_stmt
consume!(:LEFT_PAREN, "Expect '(' after 'if'.")
initializer = if match?(:SEMICOLON)
nil
elsif match?(:VAR)
var_declaration
else
expression_stmt
end
condition = check?(:SEMICOLON) ? Expr::Literal.new(true) : expression
consume!(:SEMICOLON, "Expect ';' after loop condition.")
increment = check?(:RIGHT_PAREN) ? nil : expression
consume!(:RIGHT_PAREN, "Expect ')' after for clauses.")
body = statement
if increment
body = Stmt::Block.new([
body,
Stmt::Expr.new(increment),
])
end
body = Stmt::While.new(condition, body);
if initializer
body = Stmt::Block.new([
initializer,
body,
])
end
body
end
def if_stmt
consume!(:LEFT_PAREN, "Expect '(' after 'if'.")
cond = expression
consume!(:RIGHT_PAREN, "Expect ')' after 'if'.")
then_stmt = statement
else_stmt = match?(:ELSE) ? statement : nil
Stmt::If.new(cond, then_stmt, else_stmt)
end
def print
value = expression
consume!(:SEMICOLON, "Expect ';' after value.")
Stmt::Print.new(value)
end
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def return_stmt
keyword = prev
value = check?(:SEMICOLON) ? nil : expression
consume!(:SEMICOLON, "Expect ';' after return value.")
Stmt::Return.new(keyword, value)
end
def expression_stmt
value = expression
consume!(:SEMICOLON, "Expect ';' after value.")
Stmt::Expr.new(value)
end
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def function(kind)
name = consume!(:IDENTIFIER, "Expect #{kind} name.")
consume!(:LEFT_PAREN, "Expect '(' after #{kind} name.")
params = []
unless check?(:RIGHT_PAREN)
loop do
raise ParseError.new(peek, "Can't have more than 255 parameters.") if params.size >= 255
params << consume!(:IDENTIFIER, "Expect parameter name.")
break unless match?(:COMMA)
end
end
consume!(:RIGHT_PAREN, "Expect ')' after parameters.")
consume!(:LEFT_BRACE, "Expect '{' before #{kind} body.")
body = block
Stmt::Function.new(name, params, body)
end
def block
statements = []
until check?(:RIGHT_BRACE) || eot?
statements << declaration
end
consume!(:RIGHT_BRACE, "Expect '}' after block.")
statements
end
def assignment
expr = or_
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return expr unless match?(:EQUAL)
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eq = prev
value = assignment
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case expr
when Expr::Variable
Expr::Assign.new(expr.name, value)
when Expr::Get
Expr::Set.new(expr.object, expr.name, value)
else
raise ParseError.new(eq, "Invalid assignment target.")
end
end
def or_
expr = and_
while match?(:OR)
op = prev
right = and_
expr = Expr::Logical.new(expr, op, right)
end
expr
end
def and_
expr = equality
while match?(:AND)
op = prev
right = equality
expr = Expr::Logical.new(expr, op, right)
end
expr
end
def expression = assignment
def equality
expr = comparison
while match?(:BANG_EQUAL, :EQUAL_EQUAL)
op = prev
right = comparison
expr = Expr::Binary.new(expr, op, right)
end
expr
end
def comparison
expr = term
while match?(:GREATER, :GREATER_EQUAL, :LESS, :LESS_EQUAL)
op = prev
right = term
expr = Expr::Binary.new(expr, op, right)
end
expr
end
def term
expr = factor
while match?(:MINUS, :PLUS)
op = prev
right = factor
expr = Expr::Binary.new(expr, op, right)
end
expr
end
def factor
expr = unary
while match?(:SLASH, :STAR)
op = prev
right = unary
expr = Expr::Binary.new(expr, op, right)
end
expr
end
def unary
return call unless match?(:BANG, :MINUS)
op = prev
right = unary
Expr::Unary.new(op, right)
end
def call
expr = primary
loop do
if match?(:LEFT_PAREN)
expr = finish_call(expr)
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elsif match?(:DOT)
name = consume!(:IDENTIFIER, "Expect property name after '.'.")
expr = Expr::Get.new(expr, name)
else
break
end
end
expr
end
def finish_call(callee)
args = []
if !check?(:RIGHT_PAREN)
loop do
raise ParseError.new(peek, "Can't have more than 255 arguments.") if args.size >= 255
args << expression
break unless match?(:COMMA)
end
end
paren = consume!(:RIGHT_PAREN, "Expect ')' after arguments.")
Expr::Call.new(callee, paren, args)
end
def primary
return Expr::Literal.new(false) if match?(:FALSE)
return Expr::Literal.new(true) if match?(:TRUE)
return Expr::Literal.new(nil) if match?(:NIL)
return Expr::Literal.new(prev.literal) if match?(:NUMBER, :STRING)
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if match?(:SUPER)
keyword = prev
consume!(:DOT, "Expect '.' after 'super'.")
method = consume!(:IDENTIFIER, "Expect superclass method name.")
return Expr::Super.new(keyword, method)
end
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return Expr::This.new(prev) if match?(:THIS)
return Expr::Variable.new(prev) if match?(:IDENTIFIER)
if match?(:LEFT_PAREN)
expr = expression
consume!(:RIGHT_PAREN, "Expect ')' after expression.")
return Expr::Grouping.new(expr)
end
raise ParseError.new(peek, "Expect expression.")
end
private
def match?(*types)
return false unless check?(*types)
advance!
return true
end
def consume!(type, message)
raise ParseError.new(peek, message) unless check?(type)
advance!
end
def check?(*types)
return false if eot?
types.include?(peek.type)
end
def advance!
@current += 1 unless eot?
prev
end
def eot? = peek.type === :EOF
def peek = @tokens.fetch(@current)
def prev = @tokens.fetch(@current - 1)
def synchronize!
advance!
until eot?
return if prev.type == :SEMICOLON
return if %i[CLASS FUN VAR FOR IF WHILE PRINT RETURN].include?(peek.type)
advance!
end
end
end
end