470 lines
16 KiB
CoffeeScript
470 lines
16 KiB
CoffeeScript
{listToString, listToVector, pairp, cons, car, cdr, caar, cddr, cdar,
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cadr, caadr, cadar, caddr, nilp, nil, setcdr,
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metacadr, setcar} = require "cons-lists/lists"
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{normalizeForms, normalizeForm} = require "../chapter1/astToList"
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{Node, Symbol} = require '../chapter1/reader_types'
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class LispInterpreterError extends Error
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name: 'LispInterpreterError'
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constructor: (@message) ->
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the_false_value = (cons "false", "boolean")
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# Base class that represents a value. Base class representing a LiSP
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# value, a primitive, or a function
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eq = (id1, id2) ->
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if id1 instanceof Symbol and id2 instanceof Symbol
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return id1.name == id2.name
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id1 == id2
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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: (@kont) ->
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invoke: (value, env, kont) ->
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if nilp cdr value
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@kont.resume (car value)
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else
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throw new LispInterpreterError "Continuations expect one argument"
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unwind: (value, ktarget) ->
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if (@ == ktarget) then (@kont.resume value) else (@kont.unwind value, ktarget)
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catchLookup: (tag, kk) ->
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@kont.catchLookup tag, kk
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resume: (value) ->
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throw new LispInterpreterError "Wrong continuation for #{@_type}"
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# Abstract class representing the environment
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class Environment
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lookup: -> throw new LispInterpreterError "Nonspecific invocation"
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update: -> throw new LispInterpreterError "Nonspecific invocation"
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blockLookup: -> throw new LispInterpreterError "Not an Environment"
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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: (e) -> throw new LispInterpreterError "Unknown variable #{e}"
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update: (e) -> throw new LispInterpreterError "Unknown variable #{e}"
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blockLookup: (name) -> throw new LispInterpreterError "Unknown block label #{name}"
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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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@_type = "FullEnv"
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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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blockLookup: (name, kont, value) ->
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@others.blockLookup(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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@_type = "VariableEnv"
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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: (name, 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 normalizeForms 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 exps), env, new IfCont(kont, (cadr exps), (caddr exps), env)
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class IfCont extends Continuation
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constructor: (@kont, @ift, @iff, @env) ->
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@_type = "IfCont"
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resume: (value) ->
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evaluate (if value == the_false_value then @iff else @ift), @env, @kont
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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: (@kont, @exps, @env) ->
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@_type = "BeginCont"
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resume: (v) -> evaluateBegin (cdr @exps), @env, @kont
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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 extends Continuation
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constructor: (@kont, @name, @env) ->
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@_type = "SetCont"
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resume: (value) ->
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@env.update @name, @kont, 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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@_type = "Function"
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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 new LispInterpreterError "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: (@kont, @exp, @env) ->
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@_type = "EvFunCont"
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resume: (f) ->
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evaluateArguments @exp, @env, (new ApplyCont(@kont, 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(nil)
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class ArgumentCont extends Continuation
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constructor: (@kont, @exp, @env) ->
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@_type = "ArgumentCont"
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resume: (v) ->
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evaluateArguments (cdr @exp), @env, (new GatherCont @kont, 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: (@kont, @value) ->
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@_type = "GatherCont"
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resume: (value) ->
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@kont.resume (cons @value, value)
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# Upon resumption, invoke the function.
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class ApplyCont extends Continuation
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constructor: (@kont, @fn, @env) ->
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@_type = "ApplyCont"
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resume: (value) ->
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@fn.invoke value, @env, @kont
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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: (@kont, @func) ->
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@_type = "BottomCont"
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resume: (value) ->
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@func(value)
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unwind: (value, ktarget) ->
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throw new LispInterpreterError "Obsolete continuation"
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catchLookup: (tag, kk) ->
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throw new LispInterpreterError "No associated catch"
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evaluateBlock = (label, body, env, kont) ->
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k = new BlockCont(kont, label)
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evaluateBegin body, (new BlockEnv env, label, kont), k
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class BlockCont extends Continuation
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constructor: (@kont, @label) ->
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@_type = "BlockCont"
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resume: (value) ->
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@kont.resume value
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class BlockEnv extends FullEnv
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constructor: (@others, @name, @kont) ->
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blockLookup: (name, kont, value) ->
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if (name == @name)
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kont.unwind value, @kont
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else
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@others.blockLookup(name, kont, value)
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evaluateReturnFrom = (label, form, env, kont) ->
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evaluate form, env, (new ReturnFromCont kont, env, label)
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class ReturnFromCont extends Continuation
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constructor: (@kont, @env, @label) ->
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@_type = "ReturnFromCont"
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resume: (v) ->
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@env.blockLookup @label, @kont, v
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evaluateCatch = (tag, body, env, kont) ->
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evaluate tag, env, (new CatchCont kont, body, env)
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class CatchCont extends Continuation
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constructor: (@kont, @body, @env) ->
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@_type = "CatchFromCont"
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resume: (value) ->
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evaluateBegin @body, @env, (new LabeledCont @kont, value)
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class LabeledCont extends Continuation
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constructor: (@kont, @tag) ->
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@_type = "LabeledFromCont"
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resume: (value) ->
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@kont.resume value
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catchLookup: (tag, kk) ->
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if eq tag, @tag
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evaluate kk.form, kk.env, (new ThrowingCont kk, tag, this)
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else
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@kont.catchLookup tag, kk
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class ThrowCont extends Continuation
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constructor: (@kont, @form, @env) ->
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@_type = "ThrowCont"
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resume: (value) ->
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@catchLookup value, @
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evaluateThrow = (tag, form, env, kont) ->
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evaluate tag, env, (new ThrowCont kont, form, env)
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class UnwindCont extends Continuation
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constructor: (@kont, @value, @target) ->
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resume: (value) ->
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@kont.unwind @value, @target
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class ThrowingCont extends Continuation
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constructor: (@kont, @tag, @resumecont) ->
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@_type = "ThrowingCont"
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resume: (value) ->
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@kont.unwind value, @resumecont
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evaluateUnwindProtect = (form, cleanup, env, kont) ->
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evaluate form, env, (new UnwindProtectCont kont, cleanup, env)
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class UnwindProtectCont extends Continuation
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constructor: (@kont, @cleanup, @env) ->
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@_type = "UnwindProtectCont"
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resume: (value) ->
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evaluateBegin @cleanup, @env, (new ProtectReturnCont @kont, value)
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unwind: (value, target) ->
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evaluateBegin @cleanup, @env, (new UnwindCont @kont, value, target)
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class ProtectReturnCont extends Continuation
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constructor: (@kont, @value) ->
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@_type = "ProtectReturnCont"
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resume: (value) ->
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@kont.resume @value
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class Primitive extends Value
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constructor: (@name, @nativ) ->
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@_type = "Primitive"
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invoke: (args, env, kont) ->
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@nativ.apply null, [args, env, kont]
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env_init = new NullEnv()
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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 new LispInterpreterError "Incorrect arity"
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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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definitial "#t", true
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definitial "#f", the_false_value
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definitial "nil", nil
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# FIXME: All of these things dereference to the same value!!!!
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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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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 new LispInterpreterError "Incorrect arity for call/cc"
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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 "funcall", new Primitive "funcall", (args, env, kont) ->
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if not nilp cdr args
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@kont.invoke (car args), (cdr args)
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else
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throw new LispInterpreterError "Invoke requires a function name and arguments"
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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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# Only called in rich node mode...
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astSymbolsToLispSymbols = (node) ->
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return nil if nilp node
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throw (new LispInterpreterError "Not a list of variable names") if not node.type == 'list'
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handler = (cell) ->
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return nil if nilp cell
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cons (car cell).value, (handler cdr cell)
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handler node.value
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metadata_evaluation =
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listp: (node) -> node.type == 'list'
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symbolp: (node) -> node.type == 'symbol'
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numberp: (node) -> node.type == 'number'
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stringp: (node) -> node.type == 'string'
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commentp: (node) -> node.type == 'comment'
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nvalu: (node) -> node.value
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mksymbols: (list) -> astSymbolsToLispSymbols(list)
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straight_evaluation =
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listp: (cell) -> cell.__type == 'list'
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symbolp: (cell) -> typeof cell == 'string' and cell.length > 0 and cell[0] not in ["\"", ";"]
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commentp: (cell) -> typeof cell == 'string' and cell.length > 0 and cell[0] == ";"
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numberp: (cell) -> typeof cell == 'number'
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stringp: (cell) -> typeof cell == 'string' and cell.length > 0 and cell[0] == "\""
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boolp: (cell) -> typeof cell == 'boolean'
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nullp: (cell) -> cell == null
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vectorp: (cell) -> (not straight_evaluation.listp cell) and toString.call(cell) == '[object Array]'
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recordp: (cell) -> (not cell._prototype?) and toSTring.call(cell) == '[object Object]'
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objectp: (cell) -> (cell._prototype?) and toString.call(cell) == '[object Object]'
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nilp: (cell) -> nilp(cell)
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nvalu: (cell) -> cell
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mksymbols: (cell) -> cell
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makeEvaluator = (ix = straight_evaluation, ty="straight") ->
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(exp, env, kont) ->
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if ix.symbolp exp
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return evaluateVariable (ix.nvalu exp), env, kont
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else if ([ix.numberp, ix.stringp].filter (i) -> i(exp)).length > 0
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return kont.resume ix.nvalu exp
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else if ix.listp exp
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body = ix.nvalu exp
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head = car body
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if ix.symbolp head
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switch (ix.nvalu head)
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when "quote" then evaluateQuote (cadr body), env, kont
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when "if" then evaluateIf (cdr body), env, kont
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when "begin" then evaluateBegin (cdr body), env, kont
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when "set!" then evaluateSet (ix.nvalu cadr body), (caddr body), env, kont
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when "lambda" then evaluateLambda (ix.mksymbols cadr body), (cddr body), env, kont
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when "block" then evaluateBlock (ix.nvalu cadr body), (cddr body), env, kont
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when "return-from" then evaluateReturnFrom (ix.nvalu cadr body), (caddr body), env, kont
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when "catch" then evaluateCatch (cadr body), (cddr body), env, kont
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when "throw" then evaluateThrow (cadr body), (caddr body), env, kont
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when "unwind-protect" then evaluateUnwindProtect (cadr body), (cddr body), env, kont
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else evaluateApplication (car body), (cdr body), env, kont
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else
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evaluateApplication (car body), (cdr body), env, kont
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else
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throw new LispInterpreterError("Can't handle a '#{type}'")
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nodeEval = makeEvaluator(metadata_evaluation, "node")
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lispEval = makeEvaluator(straight_evaluation, "lisp")
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evaluate = (exp, env, kont) ->
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(if exp? and (exp instanceof Node) then nodeEval else lispEval)(exp, env, kont)
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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 = interpreter
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