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require_relative "environment"
module Lox
class Interpreter
def initialize
@env = Environment.new
end
# The book does printing and error catching here, but
# we're going to do it in the runner instead.
def interpret(stmts)
stmts.each do |stmt|
evaluate(stmt)
end
end
def evaluate(stmt) = stmt.accept(self)
def visit_expr(expr)
evaluate(expr.expr)
nil
end
def visit_print(expr)
puts stringify(evaluate(expr.expr))
nil
end
def visit_var(stmt)
value = stmt.initializer&.yield_self { evaluate(_1) }
@env.define(stmt.name.lexeme, value)
nil
end
def visit_grouping(expr) = evaluate(expr.expr)
def visit_literal(expr) = expr.value
def visit_unary(expr)
right = evaluate(expr.right)
case expr.op.type
when :MINUS
check_number_operand!(expr.op, right)
-right
when :BANG then !truthy?(right)
else fail
end
end
def visit_variable(expr)
@env.get(expr.name)
end
def visit_binary(expr)
left = evaluate(expr.left)
right = evaluate(expr.right)
case expr.op.type
when :GREATER
check_number_operands!(expr.op, left, right)
left > right
when :GREATER_EQUAL
check_number_operands!(expr.op, left, right)
left >= right
when :LESS
check_number_operands!(expr.op, left, right)
left < right
when :LESS_EQUAL
check_number_operands!(expr.op, left, right)
left <= right
when :BANG_EQUAL then left != right
when :EQUAL_EQUAL then left == right
when :MINUS
check_number_operands!(expr.op, left, right)
left - right
when :PLUS
unless left.is_a?(Float) && right.is_a?(Float) || left.is_a?(String) && right.is_a?(String)
raise RuntimeError.new(expr.op, "Operands must be two numbers or two strings.")
end
left + right
when :SLASH
check_number_operands!(expr.op, left, right)
left / right
when :STAR
check_number_operands!(expr.op, left, right)
left * right
else fail
end
end
private
def truthy?(value) = !!value
def check_number_operand!(token, operand)
return if operand.is_a?(Float)
raise RuntimeError.new(token, "Operand must be a number.")
end
def check_number_operands!(token, left, right)
return if left.is_a?(Float) && right.is_a?(Float)
raise RuntimeError.new(token, "Operands must be numbers.")
end
def stringify(value)
return "nil" if value.nil?
return value.to_s.sub(/\.0$/, "") if value.is_a?(Float)
value.to_s
end
end
end