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@deadprogram
Forked from krainboltgreene/forth.rb
Created January 15, 2012 20:02
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Forth interpreter in 64 lines of Ruby
#!/usr/bin/env ruby
def pop; $stack.pop || raise(StackUnderflow); end
def push(expression); $stack << expression; end
def unary; -> { push(yield pop) }; end
def binary; -> { push(yield pop, pop) }; end
def unary_boolean; -> { push(if yield pop then 1 else 0 end) }; end
def binary_boolean; -> { push(if yield pop, pop then 1 else 0 end) }; end
def swap; $stack[-2,2] = $stack[-2,2].reverse; end
$stack = []
def new_word
raise EmptyWord if $word.size < 1
raise NestedDefinition if $word.include? ':'
name, expression = $word.shift, $word.join(' ')
$dictionary[name] = -> { parse(expression) }
$word = nil
end
def parse(expression)
puts "=> #{expression}"
begin
expression.split.each do |statement|
case
when !$skip.nil? && statement != 'fi'; next
when !$word.nil? && statement != ';'; $word << statement
when $dictionary.has_key?(statement); $dictionary[statement].call
else push statement.to_i
end
end
rescue
puts "Error: #{$!}"
end
end
$dictionary = {
'+' => binary { |a, b| a + b },
'-' => binary { |a, b| a - b },
'*' => binary { |a, b| a * b },
'/' => binary { |a, b| a * b },
'%' => binary { |a, b| a * b },
'<' => binary_boolean { |a, b| a < b },
'>' => binary_boolean { |a, b| a > b },
'=' => binary_boolean { |a, b| a == b },
'&' => binary_boolean { |a, b| a && b },
'|' => binary_boolean { |a, b| a || b },
'not' => binary_boolean { |a, b| a == 0 },
'neg' => binary { |a| -a },
'.' => -> { puts(pop) },
'..' => -> { puts($stack) },
':' => -> { $word = [] },
';' => -> { new_word },
'pop' => -> { pop },
'fi' => -> { $skip = nil },
'words' => -> { p $dictionary.keys.sort },
'if' => -> { $skip = true if pop == 0 },
'dup' => -> { push($stack.last || raise(StackUnderflow)) },
'over' => -> { push($stack.last(2).first || raise(StackUnderflow)) },
'swap' => -> { begin swap rescue raise(StackUnderflow) end }
}
puts "Ruby Forth interpreter: enter commands at the prompt"
while ARGV.size > 0; open(ARGV.shift).each { |line| parse(line) }; end
while true; print "> "; break unless gets; parse $_; end
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