Created
February 22, 2012 23:24
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Stupid Simple Forth System in Ruby
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# Example Usage: ruby froth.rb ": sq dup * ; 2 sq ." | |
class Froth | |
attr_reader :storage | |
attr_accessor :trace | |
WordDefinition = Struct.new(:name, :xt, :immediate) | |
class WordDefinition | |
def immediate? | |
immediate | |
end | |
end | |
def initialize | |
@dictionary = {} | |
@stack = [] | |
@rstack = [] | |
@storage = [] | |
@ip = 0 | |
@trace = false | |
@mode = :interpret | |
define_primitives | |
end | |
def run(string) | |
@string = string | |
xt = here | |
@storage << @dictionary["(top)"].xt | |
@storage << @dictionary["bye"].xt | |
dump if @trace | |
goto(xt) | |
end | |
private | |
def compile(string) | |
result = here | |
@words = string.split | |
while word = @words.shift | |
if word_def = @dictionary[word] | |
if @mode == :interpret || word_def.immediate? | |
execute(word_def.xt) | |
else | |
@storage << word_def.xt | |
end | |
elsif word =~ /^\d+$/ | |
if @mode == :interpret | |
@stack.push(word.to_i) | |
else | |
compile_literal(word.to_i) | |
end | |
else | |
fail "Unknown word '#{word}'" | |
end | |
end | |
result | |
end | |
def execute(xt) | |
old_ip = @ip | |
@storage[@execip] = xt | |
goto(@execip) | |
@ip = old_ip | |
end | |
def goto(initial_ip) | |
@ip = initial_ip | |
@running = true | |
while @running | |
@cp = @storage[@ip] | |
puts "STEP: @ip=#{@ip} #{@cp} #{reverse_lookup(@cp)}" if @trace | |
@ip += 1 | |
@storage[@cp].call | |
end | |
end | |
def compile_literal(n) | |
@storage << @dictionary["(lit)"].xt | |
@storage << n | |
end | |
def primitive(name, immediate=false, &block) | |
n = here | |
@storage << lambda { @storage[@cp+1].call } | |
@storage << block | |
@dictionary[name] = WordDefinition.new(name, n, immediate) | |
end | |
def define_primitives | |
primitive("(stop_running)") { @running = false } | |
@execip = here | |
@storage << 0 | |
@storage << @dictionary["(stop_running)"].xt | |
primitive("(lit)") { push(@storage[@ip]); @ip += 1 } | |
primitive(".") { puts pop } | |
primitive("+") { a = pop; b = pop; push(a+b) } | |
primitive("-") { a = pop; b = pop; push(a-b) } | |
primitive("*") { a = pop; b = pop; push(a*b) } | |
primitive("/") { a = pop; b = pop; push(a.to_i/b.to_a) } | |
primitive("dup") { a = pop; push(a); push(a) } | |
primitive("drop") { pop } | |
primitive("rot") { a = pop; b = pop; c = pop; push(b); push(a); push(c) } | |
primitive(".s") { puts @stack.join(" ") + " <#{@stack.size}>" } | |
primitive("bye") { exit } | |
primitive("dump") { dump } | |
primitive(":") { | |
name = @words.shift | |
n = here | |
@dictionary[name] = WordDefinition.new(name, n, false) | |
@storage << lambda { | |
@rstack << @ip | |
@ip = @cp + 1 | |
} | |
@mode = :compile | |
} | |
primitive("(ret)") { @ip = @rstack.pop } | |
primitive(";", true) { | |
@storage << @dictionary["(ret)"].xt | |
@mode = :interpret | |
} | |
primitive("(top)") { | |
compile(@string) | |
} | |
end | |
def here | |
@storage.size | |
end | |
def pop | |
@stack.pop | |
end | |
def push(n) | |
@stack.push(n) | |
end | |
def reverse_lookup(n) | |
@dictionary.each do |key, value| | |
return key if value.xt == n | |
end | |
nil | |
end | |
def dump | |
@storage.each_with_index do |w, i| | |
puts "#{i}: #{w} #{reverse_lookup(w)}" | |
end | |
end | |
end | |
f = Froth.new | |
if ARGV.first == '-t' | |
f.trace = true | |
ARGV.shift | |
end | |
command = ARGV.join(" ") + " bye" | |
f.run(command) |
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