293 lines
9.3 KiB
CoffeeScript
293 lines
9.3 KiB
CoffeeScript
{listToString, listToVector, pairp, cons, car, cdr, caar, cddr, cdar, cadr, caadr, cadar, caddr, nilp, nil, setcdr, metacadr, setcar} = require "cons-lists/lists"
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readline = require "readline"
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{inspect} = require "util"
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print = require "./print"
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ntype = (node) -> car node
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nvalu = (node) -> cadr node
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class Value
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# Represents the base class of a continuation. Calls to invoke resume
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# the contained continuation, which is typecast to one of the specific
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# continuation needs of conditional, sequence, etc...
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class Continuation
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constructor: (@k) ->
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invoke: (v, env, kont) ->
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if nilp cdr v
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resume @k, (car v)
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else
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throw "Continuations expect one argument", [v, env, kont]
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# Abstract class representing the environment
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class Environment
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lookup: -> throw "Nonspecific invocation"
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update: -> throw "Nonspecific invocation"
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# Base of the environment stack. If you hit this, your variable was
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# never found for lookup/update. Note that at this time in the
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# class, you have not
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class NullEnv extends Environment
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lookup: -> throw "Unknown variable"
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update: -> throw "Unknown variable"
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# This appears to be an easy and vaguely abstract handle to the
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# environment. The book is not clear on the distinction between the
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# FullEnv and the VariableEnv.
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class FullEnv extends Environment
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constructor: (@others, @name) ->
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lookup: (name, kont) ->
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@others.lookup name, kont
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update: (name, kont, value) ->
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@others.update name, kont, value
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# This is the classic environment pair; either it's *this*
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# environment, or it's a parent environment, until you hit the
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# NullEnv. Once the name has been found, the continuation is called
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# with the found value.
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class VariableEnv extends FullEnv
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constructor: (@others, @name, @value) ->
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lookup: (name, kont) ->
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if name == @name
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kont.resume @value
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else
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@others.lookup name, kont
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update: (nam, kont, value) ->
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if name == @name
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@value = value
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kont.resume value
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else
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@others.update name, kont, value
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# "Renders the quote term to the current continuation"; in a more
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# familiar parlance, calls resume in the current context with the
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# quoted term uninterpreted.
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evaluateQuote = (v, env, kont) ->
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kont.resume v
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# Evaluates the conditional expression, creating a continuation with
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# the current environment that, when resumed, evaluates either the
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# true or false branch, again in the current enviornment.
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evaluateIf = (exps, env, kont) ->
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evaluate (car e), env, new IfCont(kont, (cadr e), (caddr e), env)
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class IfCont extends Continuation
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constructor: (@k, @ift, @iff, @env) ->
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resume: (v) -> evaluate (if v then @ift else @iff), @env, @k
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# Sequences: evaluates the current expression with a continuation that
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# represents "the next expression" in the sequence. Upon resumption,
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# calls this function with that next expression.
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evaluateBegin = (exps, env, kont) ->
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if (pairp exps)
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if pairp (cdr exps)
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evaluate (car exps), env, (new BeginCont kont, exps, env)
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else
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evaluate (car exps), env, kont
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else
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kont.resume("Begin empty value")
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class BeginCont extends Continuation
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constructor: (@k, @exps, @env) ->
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resume: (v) -> evaluateBegin (cdr @exps), @env, @k
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# In this continuation, we simply pass the continuation and the name
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# to the environment to look up. The environment knows to call the
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# continuation with the value.
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evaluateVariable = (name, env, kont) ->
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env.lookup(name, kont)
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# This is the same dance as lookup, only with the continuation being
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# called after an update has been performed.
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evaluateSet = (name, exp, env, kont) ->
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evaluate exp, env, (new setCont(kont, name, env))
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class SetCont extend Continuation
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constructor: (@k, @name, @env) ->
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resume: (value) ->
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update @env, @name, @k, value
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# Calls the current contunation, passing it a new function wrapper.
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evaluateLambda = (names, exp, env, kont) ->
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kont.resume new Function names, exp, env
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# Upon invocation, evaluates the body with a new environment that
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# consists of the original names, their current values as called, and
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# the continuation an the moment of invocation, which will continue
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# (resume) execution once the function is finished.
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#
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# By the way: this is pretty much the whole the point.
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class Function extends Value
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constructor: (@variables, @body, @env) ->
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invoke: (values, env, kont) ->
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evaluateBegin @body, (extend @env, @variables, values), kont
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# Helper function to build name/value pairs for the current execution
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# context.
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extend = (env, names, values) ->
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if (pairp names) and (pairp values)
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new VariableEnv (extend env (cdr names) (cdr values)), (car names), (car values)
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else if (nilp names)
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if (nilp values) then env else throw "Arity mismatch"
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else
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new VariableEnv env, names, values
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# Now we start the invocation: this is applying the function. Let's
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# take it stepwise.
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# Create a function environment. Calls the evaluateArguments(), which
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# in turns goes down the list of arguments and creates a new
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# environment, and then the continuation is to actually appy the nev
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# environment to the existing function.
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evaluateApplication = (exp, exps, env, kont) ->
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evaluate exp, env, (new EvFunCont kont, exps, env)
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class EvFunCont extends Continuation
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constructor: (@k, @exp, @env) ->
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resume: (f) ->
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evaluateArguments (@exp, @k, new ApplyCont @k, f, @env)
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# Evaluate the first list, creating a new list of the arguments. Upon
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# completion, resume the continuation with the gather phase
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evaluateArguments = (exp, env, kont) ->
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if (pairp exp)
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evaluate (car exp), env, (new ArgumentCont kont, exp, env)
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else
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kont.resume("No more arguments")
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class ArgumentCont extends Continuation
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constructor: (@k, @exp, @env) ->
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resume: (v) ->
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evaluateArguments (cdr @env, @env, new GatherCont @k, v)
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# Gather the arguments as each ArgumentCont is resumed into a list to
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# be passed to our next step.
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class GatherCont extends Continuation
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constructor: (@k, @v) ->
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resume: (v) ->
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@k.resume (cons @v, v)
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# Upon resumption, invoke the function.
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class ApplyCont extends Continuation
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constructor: (@k, @fn, @env) ->
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resume: (v) ->
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invoke @fn, v, @env, @k
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# A special continuation that represents what we want the interpreter
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# to do when it's done processing.
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class BottomCont extends Continuation
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constructor: (@k, @f) ->
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resume: (v) ->
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@f(v)
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class Primitive extends Value
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constructor: (@name, @nativ) ->
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invoke: (args, env, kont) ->
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@nativ.apply null, (listToVector args), env, kont
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evaluate = (e, env, kont) ->
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[type, exp] = [(ntype e), (nvalu e)]
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if type == "symbol"
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return evaluateVariable exp, env, kont
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if type in ["number", "string", "boolean", "vector"]
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return exp
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if type == "list"
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head = car exp
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if (ntype head) == 'symbol'
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switch (nvalu head)
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when "quote" then evaluateQuote (cdr exp), env, kont
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when "if" then evaluateIf (cdr exp), env, kont
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when "begin" then evaluateBegin (cdr exp), env, kont
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when "set!" then evaluateSet (nvalu cadr exp), (nvalu caddr exp), env, kont
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when "lambda" then evaluateLambda (astSymbolsToLispSymbols cadr exp), (cddr exp), env, kont
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evaluateApplication (car exp), (cdr exp), env, cont
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else
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evaluateApplication (car exp), (cdr exp), env, cont
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else
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throw new Error("Can't handle a #{type}")
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definitial = (name, value = nil) ->
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env_init = new VariableEnv env_init, name, value
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name
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defprimitive = (name, nativ, arity) ->
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definitial name, new Primitive name, (args, env, kont) ->
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vmargs = listToVector(args)
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if (vmargs.length == arity)
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kont.resume (nativ.apply null, vmargs)
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else
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throw "Incorrect arity")
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the_false_value = (cons "false", "boolean")
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definitial "#t", true
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definitial "#f", the_false_value
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definitial "nil", nil
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for i in [
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"x", "y", "z", "a", "b", "c", "foo", "bar", "hux",
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"fib", "fact", "visit", "primes", "length"]
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definitial i
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defpredicate = (name, nativ, arity) ->
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defprimitive name, ((a, b) -> if nativ.call(null, a, b) then true else the_false_value), arity
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defprimitive "cons", cons, 2
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defprimitive "car", car, 2
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defprimitive "cdr", cdr, 2
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defprimitive "set-cdr!", setcdr, 2
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defprimitive "set-car!", setcar, 2
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defprimitive "+", ((a, b) -> a + b), 2
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defprimitive "*", ((a, b) -> a * b), 2
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defprimitive "-", ((a, b) -> a - b), 2
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defprimitive "/", ((a, b) -> a / b), 2
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defpredicate "lt", ((a, b) -> a < b), 2
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defpredicate "gt", ((a, b) -> a > b), 2
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defpredicate "lte", ((a, b) -> a <= b), 2
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defpredicate "gte", ((a, b) -> a >= b), 2
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defpredicate "eq?", ((a, b) -> a == b), 2
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defpredicate "pair?" ((a) -> pairp a), 1
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defpredicate "nil?" ((a) -> nilp a), 1
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defpredicate "symbol?" ((a) -> /\-?[0-9]+$/.test(a) == false), 1
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definitial "call/cc", new Primitive "call/cc", (values, env, kont) ->
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if nilp cdr values
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(car values).invoke (cons kont), env, kont
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else
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throw "Incorrect arity for call/cc", [r, k]
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definitial "apply", new Primitive "apply", (values, env, kont) ->
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if pairp cdr values
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f = car values
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args = (() ->
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(flat = (args) ->
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if nilp cdr args then (car args) else (cons (car args), (flat cdr args)))(cdr values))()
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f.invoke args, env, kont
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definitial "list", new Primitive "list", (values, env, kont) ->
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(values, env, kont) -> kont.resume(values)
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env_init = new NullEnv()
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interpreter = (ast, kont) ->
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evaluate ast, env_init, new BottomCont null, kont
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module.exports = intepreter
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