You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.

167 lines
3.6 KiB

require_relative "environment"
module Lox
class Interpreter
def initialize(env=Environment.new)
@env = env
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
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