LispInSmallPieces/chapter4/reader.coffee

{car, cdr, cons, nil, nilp, pairp, vectorToList, list} = require 'cons-lists/lists'
{inspect} = require "util"
{Node, Comment, Symbol} = require "../chapter1/reader_types"

NEWLINES   = ["\n", "\r", "\x0B", "\x0C"]
WHITESPACE = [" ", "\t"].concat(NEWLINES)

EOF = new (class Eof)()
EOO = new (class Eoo)()

class Source
  constructor: (@inStream) ->
    @index = 0
    @max = @inStream.length - 1
    @line = 0
    @column = 0

  peek: -> @inStream[@index]

  position: -> [@line, @column]

  next: ->
    c = @peek()
    return EOF if @done()
    @index++
    [@line, @column] = if @peek() in NEWLINES then [@line + 1, 0] else [@line, @column + 1]
    c

  done: -> @index > @max

# IO -> IO
skipWS = (inStream) ->
  while inStream.peek() in WHITESPACE then inStream.next()

# msg -> (IO -> Node => Error)
handleError = (message) ->
  (line, column) -> new Node('error', message, line, column)

# IO -> Node => Comment
readComment = (inStream) ->
  [line, column] = inStream.position()
  r = (while inStream.peek() != "\n" and not inStream.done()
    inStream.next()).join("")
  if not inStream.done()
    inStream.next()
  new Node 'comment', (new Comment r), line, column

# IO -> (Node => Literal => String) | Error
readString = (inStream) ->
  [line, column] = inStream.position()
  inStream.next()
  string = until inStream.peek() == '"' or inStream.done()
    if inStream.peek() == '\\'
      inStream.next()
    inStream.next()
  if inStream.done()
    return handleError("end of file seen before end of string.")(line, column)
  inStream.next()
  new Node 'string', (string.join ''), line, column

# (String) -> (Node => Literal => Number) | Nothing
readMaybeNumber = (symbol) ->
  if symbol[0] == '+'
    return readMaybeNumber symbol.substr(1)
  if symbol[0] == '-'
    ret = readMaybeNumber symbol.substr(1)
    return if ret? then -1 * ret else undefined
  if symbol.search(/^0x[0-9a-fA-F]+$/) > -1
    return parseInt(symbol, 16)
  if symbol.search(/^0[0-9a-fA-F]+$/) > -1
    return parseInt(symbol, 8)
  if symbol.search(/^[0-9]+$/) > -1
    return parseInt(symbol, 10)
  if symbol.search(/^nil$/) > -1
    return nil
  undefined

# (IO, macros) -> (IO, Node => Number | Symbol) | Error
readSymbol = (inStream, tableKeys) ->
  [line, column] = inStream.position()
  symbol = (until (inStream.done() or inStream.peek() in tableKeys or inStream.peek() in WHITESPACE)
    inStream.next()).join ''
  number = readMaybeNumber symbol
  if number?
    return new Node 'number', number, line, column
  new Node 'symbol', (new Symbol symbol), line, column


# (Delim, TypeName) -> IO -> (IO, node) | Error
makeReadPair = (delim, type) ->
  # IO -> (IO, Node) | Error
  (inStream) ->
    inStream.next()
    skipWS inStream
    [line, column] = inStream.position()
    if inStream.peek() == delim
      inStream.next()
      return new Node type, nil, line, column

    # IO -> (IO, Node) | Error
    dotted = false
    readEachPair = (inStream) ->
      [line, column] = inStream.position()
      obj = read inStream, true, null, true
      if inStream.peek() == delim
        if dotted then return obj
        return cons obj, nil
      if inStream.done() then return handleError("Unexpected end of input")(line, column)
      if dotted then return handleError("More than one symbol after dot")
      return obj if obj.type == 'error'
      if obj.type == 'symbol' and obj.value == '.'
        dotted = true
        return readEachPair inStream
      cons obj, readEachPair inStream

    ret = new Node type, readEachPair(inStream), line, column
    inStream.next()
    ret

# Type -> (IO -> (IO, Node))
prefixReader = (type) ->
  # IO -> (IO, Node)
  (inStream) ->
    [line, column] = inStream.position()
    inStream.next()
    [line1, column1] = inStream.position()
    obj = read inStream, true, null, true
    return obj if obj.type == 'error'
    new Node "list", cons((new Node("symbol", (new Symbol type), line1, column1)), cons(obj)), line, column

# I really wanted to make anything more complex than a list (like an
# object or a vector) something handled by a read macro.  Maybe in a
# future revision I can vertically de-integrate these.

readMacros =
  '"': readString
  '(': makeReadPair ')', 'list'
  ')': handleError "Closing paren encountered"
  '[': makeReadPair ']', 'vector'
  ']': handleError "Closing bracket encountered"
  '{': makeReadPair('}', 'record', (res) ->
    res.length % 2 == 0 and true or mkerr "record key without value")
  '}': handleError "Closing curly without corresponding opening."
  "`": prefixReader 'back-quote'
  "'": prefixReader 'quote'
  ",": prefixReader 'unquote'
  ";": readComment


# Given a stream, reads from the stream until a single complete lisp
# object has been found and returns the object

# IO -> Form
read = (inStream, eofErrorP = false, eofError = EOF, recursiveP = false, inReadMacros = null, keepComments = false) ->
  inStream = if inStream instanceof Source then inStream else new Source inStream
  inReadMacros = if InReadMacros? then inReadMacros else readMacros
  inReadMacroKeys = (i for i of inReadMacros)

  c = inStream.peek()

  # (IO, Char) -> (IO, Node) | Error
  matcher = (inStream, c) ->
    if inStream.done()
      return if recursiveP then handleError('EOF while processing nested object')(inStream) else nil
    if c in WHITESPACE
      inStream.next()
      return nil
    if c == ';'
      return readComment(inStream)
    ret = if c in inReadMacroKeys then inReadMacros[c](inStream) else readSymbol(inStream, inReadMacroKeys)
    skipWS inStream
    ret

  while true
    form = matcher inStream, c
    skip = (not nilp form) and (form.type == 'comment') and not keepComments
    break if (not skip and not nilp form) or inStream.done()
    c = inStream.peek()
    null
  form

# readForms assumes that the string provided contains zero or more
# forms.  As such, it always returns a list of zero or more forms.

# IO -> (Form* | Error)
readForms = (inStream) ->
  inStream = if inStream instanceof Source then inStream else new Source inStream
  return nil if inStream.done()

  # IO -> (FORM*, IO) | Error
  [line, column] = inStream.position()
  readEach = (inStream) ->
    obj = read inStream, true, null, false
    return nil if (nilp obj)
    return obj if obj.type == 'error'
    cons obj, readEach inStream

  obj = readEach inStream
  if obj.type == 'error' then obj else new Node "list", obj, line, column

exports.read = read
exports.readForms = readForms
exports.Node = Node
exports.Symbol = Symbol