LispInSmallPieces/chapter3/interpreter.coffee

{listToString, listToVector, pairp, cons, car, cdr, caar, cddr, cdar,
 cadr, caadr, cadar, caddr, nilp, nil, setcdr,
 metacadr, setcar} = require "cons-lists/lists"
{normalizeForms, normalizeForm} = require "../chapter1/astToList"
{Node, Symbol} = require '../chapter1/reader_types'

class LispInterpreterError extends Error
  name: 'LispInterpreterError'
  constructor: (@message) ->

the_false_value = (cons "false", "boolean")

# Base class that represents a value.  Base class representing a LiSP
# value, a primitive, or a function

eq = (id1, id2) ->
  if id1 instanceof Symbol and id2 instanceof Symbol
    return id1.name == id2.name
  id1 == id2

class Value

# Represents the base class of a continuation.  Calls to invoke resume
# the contained continuation, which is typecast to one of the specific
# continuation needs of conditional, sequence, etc...

class Continuation
  constructor: (@kont) ->
  invoke: (value, env, kont) ->
    if nilp cdr value
      @kont.resume (car value)
    else
      throw new LispInterpreterError "Continuations expect one argument"
  unwind: (value, ktarget) ->
    if (@kont == ktarget) then (@kont.resume value) else (@kont.unwind value, ktarget)
  catchLookup: (tag, kk) ->
    @kont.catchLookup tag, kk

# Abstract class representing the environment

class Environment
  lookup: -> throw new LispInterpreterError "Nonspecific invocation"
  update: -> throw new LispInterpreterError "Nonspecific invocation"
  blockLookup: -> throw new LispInterpreterError "Not an Environment"

# Base of the environment stack.  If you hit this, your variable was
# never found for lookup/update.  Note that at this time in the
# class, you have not

class NullEnv extends Environment
  lookup: (e) -> throw new LispInterpreterError "Unknown variable #{e}"
  update: (e) -> throw new LispInterpreterError "Unknown variable #{e}"
  blockLookup: (name) -> throw new LispInterpreterError "Unknown block label #{name}"

# This appears to be an easy and vaguely abstract handle to the
# environment.  The book is not clear on the distinction between the
# FullEnv and the VariableEnv.

class FullEnv extends Environment
  constructor: (@others, @name) ->
    @_type = "FullEnv"
  lookup: (name, kont) ->
    @others.lookup name, kont
  update: (name, kont, value) ->
    @others.update name, kont, value
  blockLookup: (name, kont, value) ->
    @others.blockLookup(name, kont, value)

# This is the classic environment pair; either it's *this*
# environment, or it's a parent environment, until you hit the
# NullEnv.  Once the name has been found, the continuation is called
# with the found value.

class VariableEnv extends FullEnv
  constructor: (@others, @name, @value) ->
    @_type = "VariableEnv"
  lookup: (name, kont) ->
    if name == @name
      kont.resume @value
    else
      @others.lookup name, kont
  update: (name, kont, value) ->
    if name == @name
      @value = value
      kont.resume value
    else
      @others.update name, kont, value

# "Renders the quote term to the current continuation"; in a more
# familiar parlance, calls resume in the current context with the
# quoted term uninterpreted.

evaluateQuote = (v, env, kont) ->
  kont.resume normalizeForms v

# Evaluates the conditional expression, creating a continuation with
# the current environment that, when resumed, evaluates either the
# true or false branch, again in the current enviornment.

evaluateIf = (exps, env, kont) ->
  evaluate (car exps), env, new IfCont(kont, (cadr exps), (caddr exps), env)


class IfCont extends Continuation
  constructor: (@kont, @ift, @iff, @env) ->
    @_type = "IfCont"
  resume: (value) ->
    evaluate (if value == the_false_value then @iff else @ift), @env, @kont

# Sequences: evaluates the current expression with a continuation that
# represents "the next expression" in the sequence.  Upon resumption,
# calls this function with that next expression.

evaluateBegin = (exps, env, kont) ->
  if (pairp exps)
    if pairp (cdr exps)
      evaluate (car exps), env, (new BeginCont kont, exps, env)
    else
      evaluate (car exps), env, kont
  else
    kont.resume("Begin empty value")

class BeginCont extends Continuation
  constructor: (@kont, @exps, @env) ->
    @_type = "BeginCont"
  resume: (v) -> evaluateBegin (cdr @exps), @env, @kont

# In this continuation, we simply pass the continuation and the name
# to the environment to look up.  The environment knows to call the
# continuation with the value.

evaluateVariable = (name, env, kont) ->
  env.lookup(name, kont)

# This is the same dance as lookup, only with the continuation being
# called after an update has been performed.

evaluateSet = (name, exp, env, kont) ->
  evaluate exp, env, (new SetCont(kont, name, env))

class SetCont extends Continuation
  constructor: (@kont, @name, @env) ->
    @_type = "SetCont"
  resume: (value) ->
    @env.update @name, @kont, value

# Calls the current contunation, passing it a new function wrapper.

evaluateLambda = (names, exp, env, kont) ->
  kont.resume new Function names, exp, env

# Upon invocation, evaluates the body with a new environment that
# consists of the original names, their current values as called, and
# the continuation an the moment of invocation, which will continue
# (resume) execution once the function is finished.
#
# By the way: this is pretty much the whole the point.

class Function extends Value
  constructor: (@variables, @body, @env) ->
    @_type = "Function"
  invoke: (values, env, kont) ->
    evaluateBegin @body, (extend @env, @variables, values), kont

# Helper function to build name/value pairs for the current execution
# context.

extend = (env, names, values) ->
  if (pairp names) and (pairp values)
    new VariableEnv (extend env, (cdr names), (cdr values)), (car names), (car values)
  else if (nilp names)
    if (nilp values) then env else throw new LispInterpreterError "Arity mismatch"
  else
    new VariableEnv env, names, values

# Now we start the invocation: this is applying the function.  Let's
# take it stepwise.

# Create a function environment.  Calls the evaluateArguments(), which
# in turns goes down the list of arguments and creates a new
# environment, and then the continuation is to actually appy the nev
# environment to the existing function.

evaluateApplication = (exp, exps, env, kont) ->
  evaluate exp, env, (new EvFunCont kont, exps, env)

class EvFunCont extends Continuation
  constructor: (@kont, @exp, @env) ->
    @_type = "EvFunCont"
  resume: (f) ->
    evaluateArguments @exp, @env, (new ApplyCont(@kont, f, @env))

# Evaluate the first list, creating a new list of the arguments.  Upon
# completion, resume the continuation with the gather phase

evaluateArguments = (exp, env, kont) ->
  if (pairp exp)
    evaluate (car exp), env, (new ArgumentCont kont, exp, env)
  else
    kont.resume(nil)

class ArgumentCont extends Continuation
  constructor: (@kont, @exp, @env) ->
    @_type = "ArgumentCont"
  resume: (v) ->
    evaluateArguments (cdr @exp), @env, (new GatherCont @kont, v)

# Gather the arguments as each ArgumentCont is resumed into a list to
# be passed to our next step.

class GatherCont extends Continuation
  constructor: (@kont, @value) ->
    @_type = "GatherCont"
  resume: (value) ->
    @kont.resume (cons @value, value)

# Upon resumption, invoke the function.

class ApplyCont extends Continuation
  constructor: (@kont, @fn, @env) ->
    @_type = "ApplyCont"
  resume: (value) ->
    @fn.invoke value, @env, @kont

# A special continuation that represents what we want the interpreter
# to do when it's done processing.

class BottomCont extends Continuation
  constructor: (@kont, @func) ->
    @_type = "BottomCont"
  resume: (value) ->
    @func(value)
  unwind: (value, ktarget) ->
    throw new LispInterpreterError "Obsolete continuation"
  catchLookup: (tag, kk) ->
    throw new LispInterpreterError "No associated catch"

evaluateBlock = (label, body, env, kont) ->
  k = new BlockCont(kont, label)
  evaluateBegin body, (new BlockEnv env, label, kont), k

class BlockCont extends Continuation
  constructor: (@kont, @label) ->
    @_type = "BlockCont"
  resume: (value) ->
    @kont.resume value

class BlockEnv extends FullEnv
  constructor: (@others, @name, @kont) ->
  blockLookup: (name, kont, value) ->
    if (name == @name)
      kont.unwind value, @kont
    else
      @others.blockLookup(name, kont, value)

evaluateReturnFrom = (label, form, env, kont) ->
  evaluate form, env, (new ReturnFromCont kont, env, label)

class ReturnFromCont extends Continuation
  constructor: (@kont, @env, @label) ->
  resume: (v) ->
    @env.blockLookup @label, @kont, v

evaluateCatch = (tag, body, env, kont) ->
  evaluate tag, env, (new CatchCont kont, body, env)

class CatchCont extends Continuation
  constructor: (@kont, @body, @env) ->
  resume: (value) ->
    evaluateBegin @body, @env, (new LabeledCont @kont, value)

class LabeledCont extends Continuation
  constructor: (@kont, @tag) ->
  resume: (value) ->
    @kont.resume value
  catchLookup: (tag, kk) ->
    if eq tag, @tag
      evaluate kk.form, kk.env, (new ThrowingCont kk, tag, this)
    else
      @kont.catchLookup tag, kk

class ThrowCont extends Continuation
  constructor: (@kont, @form, @env) ->
  resume: (value) ->
    @catchLookup value, @
  
evaluateThrow = (tag, form, env, kont) ->
  evaluate tag, env, (new ThrowCont kont, form, env)

class ThrowingCont extends Continuation
  constructor: (@kont, @tag, @resumecont) ->
  resume: (value) ->
    @resumecont.resume value

evaluateUnwindProtect = (form, cleanup, env, kont) ->
  evaluate form, env, (new UnwindProtectCont kont, cleanup, env)

class UnwindProtectCont extends Continuation
  constructor: (@kont, @cleanup, @env) ->
  resume: (value) ->
    evaluateBegin @cleanup, @env, (new ProtectReturnCont @kont, value)

class Primitive extends Value
  constructor: (@name, @nativ) ->
    @_type = "Primitive"
  invoke: (args, env, kont) ->
    @nativ.apply null, [args, env, kont]

env_init = new NullEnv()

definitial = (name, value = nil) ->
  env_init = new VariableEnv env_init, name, value
  name

defprimitive = (name, nativ, arity) ->
  definitial name, new Primitive name, (args, env, kont) ->
    vmargs = listToVector(args)
    if (vmargs.length == arity)
      kont.resume (nativ.apply null, vmargs)
    else
      throw new LispInterpreterError "Incorrect arity"

defpredicate = (name, nativ, arity) ->
  defprimitive name, ((a, b) -> if nativ.call(null, a, b) then true else the_false_value), arity

definitial "#t", true
definitial "#f", the_false_value
definitial "nil", nil

# FIXME: All of these things dereference to the same value!!!!

for i in [
  "x", "y", "z", "a", "b", "c", "foo", "bar", "hux",
  "fib", "fact", "visit", "primes", "length"]
  definitial i

defprimitive "cons", cons, 2
defprimitive "car", car, 2
defprimitive "cdr", cdr, 2
defprimitive "set-cdr!", setcdr, 2
defprimitive "set-car!", setcar, 2
defprimitive "+", ((a, b) -> a + b), 2
defprimitive "*", ((a, b) -> a * b), 2
defprimitive "-", ((a, b) -> a - b), 2
defprimitive "/", ((a, b) -> a / b), 2
defpredicate "lt", ((a, b) -> a < b), 2
defpredicate "gt", ((a, b) -> a > b), 2
defpredicate "lte", ((a, b) -> a <= b), 2
defpredicate "gte", ((a, b) -> a >= b), 2
defpredicate "eq?", ((a, b) -> a == b), 2
defpredicate "pair?", ((a) -> pairp a), 1
defpredicate "nil?", ((a) -> nilp a), 1
defpredicate "symbol?", ((a) -> /\-?[0-9]+$/.test(a) == false), 1

definitial "call/cc", new Primitive "call/cc", (values, env, kont) ->
  if nilp cdr values
    (car values).invoke (cons kont), env, kont
  else
    throw new LispInterpreterError "Incorrect arity for call/cc"

definitial "apply", new Primitive "apply", (values, env, kont) ->
  if pairp cdr values
    f = car values
    args = (() ->
      (flat = (args) ->
        if nilp (cdr args) then (car args) else (cons (car args), (flat cdr args)))(cdr values))()
    f.invoke args, env, kont

definitial "funcall", new Primitive "funcall", (args, env, kont) ->
  if not nilp cdr args
    @kont.invoke (car args), (cdr args)
  else
    throw new LispInterpreterError "Invoke requires a function name and arguments"

definitial "list", new Primitive "list", (values, env, kont) ->
  (values, env, kont) -> kont.resume(values)

# Only called in rich node mode...

astSymbolsToLispSymbols = (node) ->
  return nil if nilp node
  throw (new LispInterpreterError "Not a list of variable names") if not node.type == 'list'
  handler = (cell) ->
    return nil if nilp cell
    cons (car cell).value, (handler cdr cell)
  handler node.value

metadata_evaluation =
  listp:     (node) -> node.type == 'list'
  symbolp:   (node) -> node.type == 'symbol'
  numberp:   (node) -> node.type == 'number'
  stringp:   (node) -> node.type == 'string'
  commentp:  (node) -> node.type == 'comment'
  nvalu:     (node) -> node.value
  mksymbols: (list) -> astSymbolsToLispSymbols(list)

straight_evaluation =
  listp:     (cell) -> cell.__type == 'list'
  symbolp:   (cell) -> typeof cell == 'string' and cell.length > 0 and cell[0] not in ["\"", ";"]
  commentp:  (cell) -> typeof cell == 'string' and cell.length > 0 and cell[0] == ";"
  numberp:   (cell) -> typeof cell == 'number'
  stringp:   (cell) -> typeof cell == 'string' and cell.length > 0 and cell[0] == "\""
  boolp:     (cell) -> typeof cell == 'boolean'
  nullp:     (cell) -> cell == null
  vectorp:   (cell) -> (not straight_evaluation.listp cell) and toString.call(cell) == '[object Array]'
  recordp:   (cell) -> (not cell._prototype?) and toSTring.call(cell) == '[object Object]'
  objectp:   (cell) -> (cell._prototype?) and toString.call(cell) == '[object Object]'
  nilp:      (cell) -> nilp(cell)
  nvalu:     (cell) -> cell
  mksymbols: (cell) -> cell

makeEvaluator = (ix = straight_evaluation, ty="straight") ->
  (exp, env, kont) ->
    if ix.symbolp exp
      return evaluateVariable (ix.nvalu exp), env, kont
    else if ([ix.numberp, ix.stringp].filter (i) -> i(exp)).length > 0
      return kont.resume ix.nvalu exp
    else if ix.listp exp
      body = ix.nvalu exp
      head = car body
      if ix.symbolp head
        switch (ix.nvalu head)
          when "quote" then evaluateQuote (cadr body), env, kont
          when "if" then evaluateIf (cdr body), env, kont
          when "begin" then evaluateBegin (cdr body), env, kont
          when "set!" then evaluateSet (ix.nvalu cadr body), (caddr body), env, kont
          when "lambda" then evaluateLambda (ix.mksymbols cadr body), (cddr body), env, kont
          when "block" then evaluateBlock (ix.nvalu cadr body), (cddr body), env, kont
          when "return-from" then evaluateReturnFrom (ix.nvalu cadr body), (caddr body), env, kont
          when "catch" then evaluateCatch (cadr body), (cddr body), env, kont
          when "throw" then evaluateThrow (cadr body), (caddr body), env, kont
          when "unwind-protect" then evaluateUnwindProtect (cadr body), (cddr body), env, kont
          else evaluateApplication (car body), (cdr body), env, kont
      else
        evaluateApplication (car body), (cdr body), env, kont
    else
      throw new LispInterpreterError("Can't handle a '#{type}'")
  
nodeEval = makeEvaluator(metadata_evaluation, "node")
lispEval = makeEvaluator(straight_evaluation, "lisp")

evaluate = (exp, env, kont) ->
  (if exp? and (exp instanceof Node) then nodeEval else lispEval)(exp, env, kont)

interpreter = (ast, kont) ->
  evaluate ast, env_init, new BottomCont null, kont

module.exports = interpreter