Module: BusScheme

Defined in:
lib/cons.rb,
lib/eval.rb,
lib/lambda.rb,
lib/parser.rb,
lib/bus_scheme.rb,
lib/primitives.rb,
lib/stack_frame.rb

Defined Under Namespace

Classes: ArgumentError, AssertionFailed, BusSchemeError, Cons, EvalError, IncompleteError, Lambda, LoadError, ParseError, Primitive, StackFrame

Constant Summary collapse

SYMBOL_TABLE =

top-level scope

{}
INVALID_IDENTIFER_BEGIN =
('0' .. '9').to_a + ['+', '-', '.']
VERSION =
"0.7.6"
PROMPT =
'> '
INCOMPLETE_PROMPT =
' ... '
@@stack =
[]

Class Method Summary collapse

Class Method Details

.[](sym) ⇒ Object

Raises:


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# File 'lib/eval.rb', line 41

def [](sym)
  raise EvalError.new("Undefined symbol: #{sym.inspect}") unless in_scope?(sym)
  current_scope[sym]
end

.[]=(sym, val) ⇒ Object


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# File 'lib/eval.rb', line 46

def []=(sym, val)
  current_scope[sym] = val
end

.add_load_path(filename, load_path = BusScheme['load-path'.sym]) ⇒ Object

Raises:


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# File 'lib/bus_scheme.rb', line 75

def self.add_load_path(filename, load_path = BusScheme['load-path'.sym])
  return filename if filename.match(/^\//) or File.exist? filename
  raise LoadError, "File not found: #{filename}" if load_path.empty?
  return load_path.car + '/' + filename if File.exist? load_path.car + '/' + filename
  return add_load_path(filename, load_path.cdr)
end

.apply(function_sym, args) ⇒ Object

Call a function with given args


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# File 'lib/eval.rb', line 23

def apply(function_sym, args)
  args = args.to_a
  function = eval(function_sym)
  args.map!{ |arg| eval(arg) } unless function.special_form
  puts ' ' * stack.length + Cons.new(function_sym, args.sexp).inspect if (@trace ||= false)

  function.call_as(function_sym, *args)
end

.cons(car, cdr = nil) ⇒ Object


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# File 'lib/cons.rb', line 77

def cons(car, cdr = nil)
  Cons.new(car, cdr)
end

.current_scopeObject

Scoping methods:


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# File 'lib/eval.rb', line 33

def current_scope
  @@stack.empty? ? SYMBOL_TABLE : @@stack.last
end

.define(identifier, value) ⇒ Object


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# File 'lib/primitives.rb', line 2

def self.define(identifier, value)
  # TODO: fix if this turns out to be a good idea
  value = Primitive.new(value) if value.is_a? Proc
  BusScheme[identifier.sym] = value
end

.eval(form) ⇒ Object

Eval a form passed in as an array


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# File 'lib/eval.rb', line 12

def eval(form)
  if (form.is_a?(Cons) or form.is_a?(Array)) and form.first
    apply(form.first, form.rest)
  elsif form.is_a? Sym
    self[form.sym]
  else # well it must be a literal then
    form
  end
end

.eval_string(string) ⇒ Object

Parse a string, then eval the result


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# File 'lib/eval.rb', line 7

def eval_string(string)
  eval(parse("(top-level #{string})"))
end

.in_scope?(sym) ⇒ Boolean

Returns:

  • (Boolean)

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# File 'lib/eval.rb', line 37

def in_scope?(sym)
  current_scope.has_key?(sym) or SYMBOL_TABLE.has_key?(sym)
end

.load(filename) ⇒ Object

Load a file if on the load path or absolute


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# File 'lib/bus_scheme.rb', line 64

def self.load(filename)
  begin
    loaded_files.push filename
    eval_string File.read(add_load_path(filename))
    loaded_files.pop
  rescue
    loaded_files.pop
    raise
  end
end

.loaded_filesObject

For stack traces


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# File 'lib/bus_scheme.rb', line 83

def self.loaded_files
  (@loaded_files ||= ["(eval)"])
end

.parse(input) ⇒ Object

Turn an input string into an S-expression


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# File 'lib/parser.rb', line 7

def parse(input)
  @@lines = 1
  # TODO: should sexp it as it's being constructed, not after
  parse_tokens(tokenize(input).flatten).sexp(true)
end

.parse_dots_into_cons(list) ⇒ Object

Parse a “dotted cons” (1 . 2) into (cons 1 2)


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# File 'lib/parser.rb', line 40

def parse_dots_into_cons(list)
  if(list && list.length > 0 && list[1] == :'.')
    [:cons.sym, list.first, *list[2 .. -1]]
  else
    list
  end
end

.parse_list(tokens) ⇒ Object

Nest a list from a 1-dimensional list of tokens

Raises:


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# File 'lib/parser.rb', line 25

def parse_list(tokens)
  list = []
  while element = tokens.shift and element != :')'
    if element == :'('
      list << parse_list(tokens)
    else
      list << element
    end
  end
  raise IncompleteError unless element == :')'

  parse_dots_into_cons list
end

.parse_tokens(tokens) ⇒ Object

Turn a list of tokens into a properly-nested array


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# File 'lib/parser.rb', line 14

def parse_tokens(tokens)
  token = tokens.shift
  if token == :'('
    parse_list(tokens)
  else
    raise ParseError unless tokens.empty?
    token # atom
  end
end

.pop_token(input) ⇒ Object

Take a token off the input string and return it


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# File 'lib/parser.rb', line 58

def pop_token(input)
  # can't use ^ since it matches line beginnings in mid-string
  token = case input
          when /\A(\s|;.*$)/ # ignore whitespace and comments
            @@lines += Regexp.last_match[1].count("\n")
            input[0 .. Regexp.last_match[1].length - 1] = ''
            return pop_token(input)
          when /\A(\(|\))/ # parens
            Regexp.last_match[1].intern
            #              when /\A#([^\)])/
          when /\A#\(/ # vector
            input[0 ... 2] = ''
            return [:'(', :vector.sym, tokenize(input)]
          when /\A'/ # single-quote
            input[0 ... 1] = ''
            return [:'(', :quote.sym,
                    if input[0 ... 1] == '('
                      tokenize(input)
                    else
                      pop_token(input)
                    end,
                    :')']
          when /\A(-?\+?[0-9]*\.[0-9]+)/ # float
            Regexp.last_match[1].to_f
          when /\A(\.)/ # dot (for pair notation), comes after float to pick up any dots that float doesn't accept
            :'.'
          when /\A(-?[0-9]+)/ # integer
            Regexp.last_match[1].to_i
          when /\A("(.*?)")/m # string
            Regexp.last_match[2]
            # Official Scheme valid identifiers:
            # when /\A([A-Za-z!\$%&\*\.\/:<=>\[email protected]\^_~][A-Za-z0-9!\$%&\*\+\-\.\/:<=>\[email protected]\^_~]*)/ # symbol
            # when /\A([^-0-9\. \n\)][^ \n\)]*)/
          when /\A([^ \n\)]+)/ # symbols
            # puts "#{Regexp.last_match[1]} - #{@@lines}"
            # cannot begin with a character that may begin a number
            sym = Regexp.last_match[1].sym
            sym.file, sym.line = [BusScheme.loaded_files.last, @@lines]
            raise ParseError, "Invalid identifier: #{sym}" if INVALID_IDENTIFER_BEGIN.include? sym[0 .. 0] and sym.size > 1
            sym
          else
            raise ParseError if input =~ /[^\s ]/
          end

  # Remove the matched part from the string
  input[0 .. Regexp.last_match[1].length - 1] = '' if token
  return token
end

.replObject

Read-Eval-Print-Loop


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# File 'lib/bus_scheme.rb', line 39

def self.repl
  loop do
    puts begin
           input = Readline.readline(PROMPT)
           exit if input.nil? # only Ctrl-D produces nil here it seems
           begin # allow for multiline input
             result = BusScheme.eval_string(input).inspect
           rescue IncompleteError
             input += "\n" + Readline.readline(INCOMPLETE_PROMPT)
             retry
           end
           Readline::HISTORY.push(input)
           result
         rescue Interrupt
           'Type "(quit)" or press Ctrl-D to leave Bus Scheme.'
         rescue BusSchemeError => e
           "Error: #{e}"
         rescue StandardError => e
           "You found a bug in Bus Scheme!\n" +
             "#{e.class}: #{e}\n#{e.backtrace.join("\n")}"
         end
  end
end

.special_form(identifier, value) ⇒ Object


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# File 'lib/primitives.rb', line 8

def self.special_form(identifier, value)
  # TODO: fix if this turns out to be a good idea
  value = Primitive.new(value) if value.is_a? Proc
  value.special_form = true
  BusScheme[identifier.sym] = value
end

.stackObject


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# File 'lib/eval.rb', line 56

def stack
  @@stack
end

.stacktraceObject

Tracing methods:


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# File 'lib/eval.rb', line 51

def stacktrace
  # TODO: notrace is super-duper-hacky!
  @@stack.reverse.map{ |frame| frame.trace if frame.respond_to? :trace }.compact
end

.tokenize(input) ⇒ Object

Split an input string into lexically valid tokens


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# File 'lib/parser.rb', line 49

def tokenize(input)
  [].affect do |tokens|
    while token = pop_token(input)
      tokens << token
    end
  end
end