/
minilisp
executable file
·233 lines (211 loc) · 6.38 KB
/
minilisp
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#!/usr/bin/env ruby
require 'sexpistol'
require 'readline'
module MiniLisp
class Environment
attr_accessor :parent
def initialize(parent = nil)
@parent = parent
@table = {}
end
def find(name)
return @table[name] if @table.has_key?(name)
return nil if @parent.nil?
return @parent.find(name)
end
def define(name, value)
@table[name] = value
end
end
class Interpreter
attr_accessor :base_environment,
:current_environment
def initialize
@base_environment = @current_environment = MiniLisp::Environment.new
end
def run(program)
expressions = Sexpistol.new.parse_string(program)
result = nil
expressions.each do |expression|
result = evaluate(expression)
end
return result
end
def evaluate(expression)
return @current_environment.find(expression) if expression.is_a? Symbol
return expression unless expression.is_a? Array
if expression[0] == :define
return @current_environment.define expression[1],
evaluate(expression[2])
elsif expression[0] == :native_function
return eval expression[1]
else # function call
function = evaluate(expression[0])
arguments = expression.slice(1, expression.length)
return function.call(arguments, self)
end
end
end
end
Interpreter = MiniLisp::Interpreter.new
Interpreter.run(%q!(define +
(native_function "Proc.new() do |arguments, interpreter|
arguments.inject(0) {|sum, x| sum += interpreter.evaluate(x)};
end"))!)
Interpreter.run(%q!(define -
(native_function "
Proc.new() do |arguments, interpreter|
tmp = arguments.map {|item| interpreter.evaluate(item)}
tmp.inject {|sum, n| sum - n}
end
"))!)
Interpreter.run(%q!(define *
(native_function "Proc.new() do |arguments, interpreter|
arguments.inject(1) {|sum, x| sum *= interpreter.evaluate(x)};
end"))!)
Interpreter.run(%q!(define /
(native_function "
Proc.new() do |arguments, interpreter|
tmp = arguments.map {|item| interpreter.evaluate(item)}
tmp.inject {|sum, n| sum / n}
end
"))!)
Interpreter.run(%q!(define display
(native_function "
Proc.new() do |arguments, interpreter|
output = interpreter.evaluate(arguments[0])
print output
output
end
"))!)
Interpreter.run(%q!(define if
(native_function "
Proc.new() do |arguments, interpreter|
if(interpreter.evaluate(arguments[0]))
interpreter.evaluate(arguments[1])
else
interpreter.evaluate(arguments[2]) unless(arguments[2].nil?)
end
end
"))!)
Interpreter.run(%q!
(define >
(native_function "
Proc.new() do |arguments, interpreter|
arguments.slice(1, arguments.length).all? do |x|
interpreter.evaluate(arguments[0]) > interpreter.evaluate(x)
end
end
"))!)
Interpreter.run(%q!
(define <
(native_function "
Proc.new() do |arguments, interpreter|
arguments.slice(1, arguments.length).all? do |x|
interpreter.evaluate(arguments[0]) < interpreter.evaluate(x)
end
end
"))!)
Interpreter.run(%q/(define =
(native_function "
Proc.new() do |arguments, interpreter|
!(arguments.map{|x| interpreter.evaluate(x) ==
interpreter.evaluate(arguments[0])}).include?( false )
end"))/)
Interpreter.run(%q!
(define lambda
(native_function "
Proc.new() do |arguments, interpreter|
formals = arguments[0]
body = arguments.slice(1, arguments.length)
if formals.is_a? Array
# detect if any formal names have been used more than once
error_message = 'Formal {FORMAL} declared more than once'
formals.each_index do |x|
tmp = formals.dup
tmp.delete_at(x)
raise(error_message.gsub('{FORMAL}',
formals[x])) if tmp.include? formals[x]
end
end
sub_env = Environment.new(interpreter.current_environment)
execute_body = Proc.new() do |body, environment, interpreter|
interpreter.current_environment = environment
result = nil
body.each do |expression|
result = interpreter.evaluate(expression)
end
interpreter.current_environment = environment.parent
result
end
if formals.is_a?(Array) && formals.include?(:'.')
Proc.new() do |arguments, interpreter|
args = arguments.dup
named_formals = formals.slice(0, formals.index(:'.'))
list_formal = formals[formals.index(:'.') + 1]
named_formals.each_index do |i|
sub_env.define(named_formals[i], interpreter.evaluate(args.shift))
end
sub_env.define(list_formal, args)
execute_body.call(body, sub_env, interpreter)
end
elsif formals.is_a? Array
Proc.new() do |arguments, interpreter|
formals.each_index do |i|
sub_env.define(formals[i], interpreter.evaluate(arguments[i]))
end
execute_body.call(body, sub_env, interpreter)
end
elsif formals.is_a? Symbol
Proc.new() do |arguments, interpreter|
arguments = arguments.map {|x| interpreter.evaluate(x) }
sub_env.define(formals, arguments)
execute_body.call(body, sub_env, interpreter)
end
end
end
"))!)
Interpreter.run(%q!(define quote
(native_function "
Proc.new() do |arguments, interpreter|
arguments[0]
end
"))!)
Interpreter.run(%q!(define cons
(native_function "
Proc.new() do |arguments, interpreter|
arg_1 = interpreter.evaluate(arguments[0])
arg_2 = interpreter.evaluate(arguments[1]).dup
if arg_2.is_a? Array
arg_2.unshift arg_1
else
[arg_1, arg_2]
end
end
"))!)
Interpreter.run(%q!(define car
(native_function "
Proc.new() do |argument, interpreter|
list = interpreter.evaluate(argument[0])
list[0]
end
"))!)
Interpreter.run(%q!(define cdr
(native_function "
Proc.new() do |argument, interpreter|
list = interpreter.evaluate(argument[0])
list.slice(1, list.length)
end
"))!)
loop do
line = Readline::readline('> ')
break if line.nil? || line == 'quit'
Readline::HISTORY.push(line)
begin
result = Interpreter.run(line)
print result.to_s+"\n"
rescue
print $!
print "\n"
end
end