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