[refactor] Is this the functor/applicative/monadic life?

This is a big change.  For chapter 5, I ripped out all line/column
tracking and most error handling from the parser; it's now a plain
ol' Lisp parser, and if it's not close to CL 22.1.1, it's a hell of
a lot closer than it used to be.

In doing so, I reduced the size of the parser by about 40 lines.

TrackingReader takes every function in a Reader and puts that
debugging information *back*.  It turns out that all that information
was prelude and postlude to the act of parsing; by wrapping each
function in a decorator I was able to restore all that information,
and I only had to get it right exactly *once*.

In functional programming terms, this lifts:

	IO -> (atom | list)

to:

	IO with tracking -> Node (atom | list) with tracking

It's a totally free win without having to do much extra work.

Now, this check-in isn't perfect.  The tracking reader is still
tossing on some things, and because I don't have a robust type
system (it is Coffeescript, after all), I'm having to do the
decorating and wrapping by hand.  But I'm definitely on my way
to understanding the issues, and having a grasp on functors and
monoids.

chapter5/reader.coffee

@@ -1,6 +1,6 @@
 {car, cdr, cons, nil, nilp, pairp, vectorToList, list} = require 'cons-lists/lists'
 {inspect} = require "util"
-{Node, Comment, Symbol} = require "../chapter5/reader_types"
+{Comment, Symbol} = require "../chapter5/reader_types"
 
 NEWLINES   = ["\n", "\r", "\x0B", "\x0C"]
 WHITESPACE = [" ", "\t"].concat(NEWLINES)
@@ -8,6 +8,10 @@ WHITESPACE = [" ", "\t"].concat(NEWLINES)
 EOF = new (class Eof)()
 EOO = new (class Eoo)()
 
+class ReadError extends Error
+  name: 'LispInterpreterError'
+  constructor: (@message) ->
+
 class Source
   constructor: (@inStream) ->
     @index = 0
@@ -32,33 +36,6 @@ class Source
 skipWS = (inStream) ->
   while inStream.peek() in WHITESPACE then inStream.next()
 
-# msg -> (IO -> IO, Node)
-handleError = (message) ->
-  (line, column) -> new Node('error', message, line, column)
-
-# IO -> (IO, Node)
-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 -> (IO, Node) | 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) -> (Symbol | Number) | Nothing
 readMaybeNumber = (symbol) ->
   if symbol[0] == '+'
     return readMaybeNumber symbol.substr(1)
@@ -75,129 +52,116 @@ readMaybeNumber = (symbol) ->
     return nil
   undefined
 
-# (IO, macros) -> (IO, Node => Number | Symbol) | Error
+# (Delim, TypeName) -> IO -> (IO, Node) | Errorfor
-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 (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()
+      inStream.next() unless inStream.done()
-      return new Node type, nil, line, column
+      return if type then cons((new Symbol type), nil) else nil
 
     # IO -> (IO, Node) | Error
     dotted = false
-    readEachPair = (inStream) ->
+    readEachPair = (inStream) =>
-      [line, column] = inStream.position()
+      obj = @read inStream, true, null, true
-      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)
+      return obj if obj instanceof ReadError
-      if dotted then return handleError("More than one symbol after dot")
+      if inStream.done() then return new ReadError "Unexpected end of input"
-      return obj if obj.type == 'error'
+      if dotted then return new ReadError "More than one symbol after dot in list"
-      if obj.type == 'symbol' and obj.value == '.'
+      if obj instanceof Symbol and obj.name == '.'
         dotted = true
         return readEachPair inStream
       cons obj, readEachPair inStream
 
-    ret = new Node type, readEachPair(inStream), line, column
+    obj = readEachPair(inStream)
     inStream.next() 
-    ret
+    if type then cons((new Symbol type), obj) else obj
 
 # 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'
+    return obj if obj instanceof ReadError
-    new Node "list", cons((new Node("symbol", (new Symbol type), line1, column1)), cons(obj)), line, column
+    cons((new Symbol type), obj)
 
-# I really wanted to make anything more complex than a list (like an
+class Reader
-# object or a vector) something handled by a read macro.  Maybe in a
+  "symbol": (inStream) ->
-# future revision I can vertically de-integrate these.
+    symbol = (until (inStream.done() or @[inStream.peek()]? or inStream.peek() in WHITESPACE)
+      inStream.next()).join ''
+    number = readMaybeNumber symbol
+    if number?
+      return number
+    new Symbol symbol
 
-readMacros =
+  "read": (inStream, eofErrorP = false, eofError = EOF, recursiveP = false, keepComments = false) ->
-  '"': 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 -> IO, Node
-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) ->
+    matcher = (inStream, c) =>
       if inStream.done()
-      return if recursiveP then handleError('EOF while processing nested object')(inStream) else nil
+        return if recursiveP then (new ReadError 'EOF while processing nested object') 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)
+      ret = if @[c]? then @[c](inStream) else @symbol(inStream)
       skipWS inStream
       ret
   
     while true
       form = matcher inStream, c
-    skip = (not nilp form) and (form.type == 'comment') and not keepComments
+      skip = (not nilp form) and (form instanceof 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
+  '(': makeReadPair ')', null
-# forms.  As such, it always returns a list of zero or more forms.
 
-# IO -> (IO, Nodes* | Error)
+  '[': makeReadPair ']', 'vector'
-readForms = (inStream) ->
-  inStream = if inStream instanceof Source then inStream else new Source inStream
-  return nil if inStream.done()
 
-  # IO -> (IO, Nodes* | Error
+  '{': makeReadPair('}', 'record', (res) ->
-  [line, column] = inStream.position()
+    res.length % 2 == 0 and true or mkerr "record key without value")
-  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
+  '"': (inStream) ->
-  if obj.type == 'error' then obj else new Node "list", obj, line, column
+    inStream.next()
+    s = until inStream.peek() == '"' or inStream.done()
+      if inStream.peek() == '\\'
+        inStream.next()
+      inStream.next()
+    return (new ReadError "end of file seen before end of string") if inStream.done()
+    inStream.next()
+    s.join ''
 
-exports.read = read
+  ')': (inStream) -> new ReadError "Closing paren encountered"
-exports.readForms = readForms
+
-exports.Node = Node
+  ']': (inStream) -> new ReadError "Closing bracket encountered"
-exports.Symbol = Symbol
+
+  '}': (inStream) -> new ReadError "Closing curly without corresponding opening."
+
+  "`": prefixReader 'back-quote'
+
+  "'": prefixReader 'quote'
+
+  ",": prefixReader 'unquote'
+
+  ";": (inStream) ->
+    r = (while inStream.peek() != "\n" and not inStream.done()
+      inStream.next()).join("")
+    inStream.next() if not inStream.done()
+    new Comment r
+
+exports.Source = Source
+exports.ReadError = ReadError  
+exports.Reader = Reader
+reader = new Reader()
+exports.read = -> reader.read.apply(reader, arguments)

chapter5/reader_rawtoform.coffee

@@ -0,0 +1,27 @@
+{car, cdr, cons, listp, nilp, nil,
+ list, pairp, listToString} = require 'cons-lists/lists'
+
+{Symbol, Comment} = require './reader_types'
+
+exports.normalize = normalize = (form) ->
+  return nil if nilp form
+
+  methods =
+    'vector': (form) ->
+      until (nilp form) then p = normalize(car form); form = cdr form; p
+
+    'record': (form) ->
+      o = Object.create(null)
+      until (nilp form)
+        o[(normalize car form)] = (normalize car cdr form)
+        form = cdr cdr form
+        null
+      o
+
+  if (listp form) and (car form) instanceof Symbol
+    if (car form).name in ['vector', 'record']
+      methods[(car form).name](cdr form)
+    else
+      cons (normalize car form), (normalize cdr form)
+  else
+    form

chapter5/reader_tracktoform.coffee

@@ -0,0 +1,37 @@
+{car, cdr, cons, listp, nilp, nil,
+ list, pairp, listToString} = require 'cons-lists/lists'
+
+{Symbol, Comment} = require './reader_types'
+
+exports.normalize = normalize = (form) ->
+  _normalize = (form) ->
+    return nil if nilp form.v
+  
+    methods =
+      'vector': (form) ->
+        until (nilp form.v) then p = normalize(car form.v); form = cdr form.v; p
+  
+      'record': (form) ->
+        o = Object.create(null)
+        until (nilp form.v)
+          o[(normalize car form.v)] = (normalize car cdr form.v)
+          form = cdr cdr form.v
+          null
+        o
+
+      'list': (form) ->
+        handle = (form) ->
+          return nil if (nilp form)
+          return _normalize(form) if not (listp form)
+          cons (_normalize car form), (handle cdr form)
+        handle(form.v)
+  
+    if (listp form.v)
+      if (car form.v) instanceof Symbol and (car form.v).name in ['vector', 'record']
+        methods[(car form.v).name](cdr form.v)
+      else
+        methods.list(form)
+    else
+      form.v
+
+  _normalize(form)

chapter5/tracking_reader.coffee

@@ -0,0 +1,22 @@
+{Reader, ReadError, Source} = require './reader'
+{Node} = require './reader_types'
+
+liftToTrack = (f) ->
+  (ioStream) ->
+    ioStream = if ioStream instanceof Source then ioStream else new Source ioStream
+    [line, column] = ioStream.position()
+    obj = f.apply(this, arguments)
+    if obj instanceof ReadError
+      obj['line'] = line
+      obj['column'] = column
+      return obj
+    if obj instanceof Node then obj else new Node obj, line, column
+
+TrackingReader = class
+for own key, func of Reader::
+  TrackingReader::[key] = liftToTrack(func)
+
+exports.ReadError = ReadError  
+exports.Reader = TrackingReader
+exports.reader = reader = new TrackingReader()
+exports.read = -> reader.read.apply(reader, arguments)

test/reader5_samples.coffee

@@ -0,0 +1,22 @@
+{cons, nil} = require "cons-lists/lists"
+exports.samples = [
+  ['nil', nil]
+  ['0', 0]
+  ['1', 1]
+  ['500', 500]
+  ['0xdeadbeef', 3735928559]
+  ['"Foo"', 'Foo']
+  ['(1)', cons(1)]
+  ['(1 2)', cons(1, (cons 2))]
+  ['(1 2 )', cons(1, (cons 2))]
+  ['( 1 2 )', cons(1, (cons 2))]
+  ['(   1   2   )', cons(1, (cons 2))]
+  ['("a" "b")', cons("a", (cons "b"))]
+  ['("a" . "b")', cons("a", "b")]
+  ['[]', []]
+  ['{}', {}]
+  ['[1 2 3]', [1, 2, 3]]
+  # ['(1 2 3', 'error']
+  ['{"foo" "bar"}', {foo: "bar"}]
+]
+

test/test_reader5a.coffee

@@ -0,0 +1,15 @@
+chai = require 'chai'
+chai.should()
+expect = chai.expect
+
+{cons, nil, nilp} = require "cons-lists/lists"
+{read} = require '../chapter5/reader'
+{normalize} = require '../chapter5/reader_rawtoform'
+{samples} = require './reader5_samples'
+
+describe "Lisp reader functions", ->
+  for [t, v] in samples
+    do (t, v) ->
+      it "should interpret #{t} as #{v}", ->
+        res = normalize read t
+        expect(res).to.deep.equal(v)

test/test_reader5b.coffee

@@ -0,0 +1,15 @@
+chai = require 'chai'
+chai.should()
+expect = chai.expect
+
+{cons, nil, nilp} = require "cons-lists/lists"
+{read} = require '../chapter5/tracking_reader'
+{normalize} = require '../chapter5/reader_tracktoform'
+{samples} = require './reader5_samples'
+
+describe "Tracker reader functions", ->
+  for [t, v] in samples
+    do (t, v) ->
+      it "should interpret #{t} as #{v}", ->
+        res = normalize read t
+        expect(res).to.deep.equal(v)