require_relative "environment" module Lox class Interpreter def initialize(env=Environment.new) @globals = env @env = @globals @globals.define("clock", Class.new { def arity = 0 def call(*) = Time.now.to_f def to_s = "" }) 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| execute(stmt) end end def evaluate(expr) = expr.accept(self) def execute(stmt) = stmt.accept(self) def visit_block(stmt) execute_block(stmt.stmts, Environment.new(@env)) nil end def execute_block(stmts, env) prev_env = @env @env = env stmts.each do |stmt| execute(stmt) end ensure @env = prev_env end def visit_expr(expr) evaluate(expr.expr) nil end def visit_if(stmt) if truthy?(evaluate(stmt.cond)) evaluate(stmt.then) elsif stmt.else evaluate(stmt.else) end 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_while(stmt) while truthy?(evaluate(stmt.cond)) execute(stmt.body) end nil end def visit_grouping(expr) = evaluate(expr.expr) def visit_literal(expr) = expr.value def visit_logical(expr) left = evaluate(expr.left) if expr.op.type == :OR return left if truthy?(left) else return left unless truthy?(left) end evaluate(expr.right) end 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_assign(expr) value = evaluate(expr.value) @env.assign(expr.name, value) value 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 def visit_call(expr) func = evaluate(expr.callee) args = expr.args.map { evaluate(_1) } raise RuntimeError.new(expr.paren, "Can only call functions and classes.") unless func.respond_to?(:call) raise RuntimeError.new(expr.paren, "Expected #{func.arity} arguments but got #{args.size}.") unless args.size == func.arity func.call(self, args) 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