// L7-eval: CPS version of L5 with concrete data-structure continuations import { map, repeat, zipWith } from "ramda"; import { AppExp, CExp, DefineExp, Exp, IfExp, LetrecExp, LetExp, ProcExp, Program, SetExp, VarDecl } from '../L5/L5-ast'; import { isBoolExp, isLitExp, isNumExp, isPrimOp, isStrExp, isVarRef } from "../L5/L5-ast"; import { parseL5Exp, unparse } from "../L5/L5-ast"; import { isAppExp, isDefineExp, isIfExp, isLetrecExp, isLetExp, isProcExp, isSetExp } from "../L5/L5-ast"; import { applyEnv, applyEnvBdg, globalEnvAddBinding, makeExtEnv, setFBinding, theGlobalEnv, Env, ExtEnv } from "../L5/L5-env"; import { isClosure, makeClosure, Closure, Value, valueToString } from "../L5/L5-value"; import { isEmpty, first, rest } from '../shared/list'; import { applyPrimitive } from "../L5/evalPrimitive"; import { Result, makeOk, makeFailure, bind, either } from "../shared/result"; import { parse as p } from "../shared/parser"; // ======================================================== // Continuation datatype type Cont = (res: Result<Value>) => Result<Value>; type ContArray = (results: Result<Value[]>) => Result<Value>; const applyCont = (cont: Cont, val: Result<Value>) => cont(val); const applyContArray = (cont: ContArray, val: Result<Value[]>) => cont(val); // ======================================================== // Eval functions export const evalCont = (exp: CExp, env: Env, cont: Cont): Result<Value> => isNumExp(exp) ? applyCont(cont, makeOk(exp.val)) : isBoolExp(exp) ? applyCont(cont, makeOk(exp.val)) : isStrExp(exp) ? applyCont(cont, makeOk(exp.val)) : isPrimOp(exp) ? applyCont(cont, makeOk(exp)) : isVarRef(exp) ? applyCont(cont, applyEnv(env, exp.var)) : isLitExp(exp) ? applyCont(cont, makeOk(exp.val)) : isIfExp(exp) ? evalIf(exp, env, cont) : isProcExp(exp) ? evalProc(exp, env, cont) : isLetExp(exp) ? evalLet(exp, env, cont) : isLetrecExp(exp) ? evalLetrec(exp, env, cont) : isSetExp(exp) ? evalSet(exp, env, cont) : isAppExp(exp) ? evalApp(exp, env, cont) : exp; export const isTrueValue = (x: Value): boolean => ! (x === false); const evalIf = (exp: IfExp, env: Env, cont: Cont): Result<Value> => evalCont(exp.test, env, makeIfCont(exp, env, cont)); const makeIfCont = (exp: IfExp, env: Env, cont: Cont) => (testVal: Result<Value>) => bind(testVal, test => isTrueValue(test) ? evalCont(exp.then, env, cont) : evalCont(exp.alt, env, cont)); const evalProc = (exp: ProcExp, env: Env, cont: Cont): Result<Value> => applyCont(cont, makeOk(makeClosure(exp.args, exp.body, env))); // Return the vals (rhs) of the bindings of a let expression const letVals = (exp: LetExp | LetrecExp): CExp[] => map((b) => b.val, exp.bindings); // Return the vars (lhs) of the bindings of a let expression const letVars = (exp: LetExp | LetrecExp): string[] => map((b) => b.var.var, exp.bindings); // LET: Direct evaluation rule without syntax expansion // compute the values, extend the env, eval the body. const evalLet = (exp: LetExp, env: Env, cont: Cont): Result<Value> => evalExps(letVals(exp), env, makeLetCont(exp, env, cont)); const makeLetCont = (exp: LetExp, env: Env, cont: Cont) => (vals: Result<Value[]>) => bind(vals, (values: Value[]) => evalSequence(exp.body, makeExtEnv(letVars(exp), values, env), cont)); // Evaluate an array of expressions in sequence - pass the result of the last element to cont // @Pre: exps is not empty export const evalSequence = (exps: Exp[], env: Env, cont: Cont): Result<Value> => isEmpty(exps) ? applyCont(cont, makeFailure("Empty Sequence")) : evalSequenceFR(first(exps), rest(exps), env, cont); const evalSequenceFR = (exp: Exp, exps: Exp[], env: Env, cont: Cont): Result<Value> => isDefineExp(exp) ? evalDefineExps(exp, exps, cont) : isEmpty(exps) ? evalCont(exp, env, cont) : evalCont(exp, env, makeFirstCont(exps, env, cont)); export const makeFirstCont = (exps: Exp[], env: Env, cont: Cont) => (firstVal: Result<Value>) => bind(firstVal, _ => evalSequence(exps, env, cont)); // define always updates theGlobalEnv // We only expect defineExps at the top level. export const evalDefineExps = (exp: DefineExp, exps: Exp[], cont: Cont): Result<Value> => evalCont(exp.val, theGlobalEnv, makeDefCont(exp, exps, cont)); export const makeDefCont = (exp: DefineExp, exps: Exp[], cont: Cont) => (rhsVal: Result<Value>) => bind(rhsVal, rhs => { globalEnvAddBinding(exp.var.var, rhs); return evalSequence(exps, theGlobalEnv, cont); }); // Evaluate an array of expressions - pass the result as an array to the continuation export const evalExps = (exps: Exp[], env: Env, cont: ContArray): Result<Value> => isEmpty(exps) ? applyContArray(cont, makeOk([])) : evalExpsFR(first(exps), rest(exps), env, cont) const evalExpsFR = (exp: Exp, exps: Exp[], env: Env, cont: ContArray): Result<Value> => isDefineExp(exp) ? applyContArray(cont, bind(unparse(exp), e => makeFailure(`Unexpected define: ${JSON.stringify(e, null, 2)}`))) : evalCont(exp, env, makeExpsCont1(exps, env, cont)); const makeExpsCont1 = (exps: Exp[], env: Env, cont: ContArray): Cont => (firstVal: Result<Value>) => bind(firstVal, first => evalExps(exps, env, makeExpsCont2(first, cont))); const makeExpsCont2 = (firstVal: Value, cont: ContArray): ContArray => (restVals: Result<Value[]>) => bind(restVals, rest => applyContArray(cont, makeOk([firstVal, ...rest]))); // LETREC: Direct evaluation rule without syntax expansion // 1. extend the env with vars initialized to void (temporary value) // 2. compute the vals in the new extended env // 3. update the bindings of the vars to the computed vals // 4. compute body in extended env export const evalLetrec = (exp: LetrecExp, env: Env, cont: Cont): Result<Value> => { const vars = letVars(exp); const vals = letVals(exp); const extEnv = makeExtEnv(vars, repeat(undefined, vars.length), env); // Compute the vals in the extended env return evalExps(vals, extEnv, makeLetrecCont(exp, extEnv, cont)); } export const makeLetrecCont = (exp: LetrecExp, extEnv: ExtEnv, cont: Cont): ContArray => (cvals: Result<Value[]>) => bind(cvals, vals => { zipWith((bdg, val) => setFBinding(bdg, val), extEnv.frame.fbindings, vals); return evalSequence(exp.body, extEnv, cont); }); // L4-eval-box: Handling of mutation with set! export const evalSet = (exp: SetExp, env: Env, cont: Cont): Result<Value> => evalCont(exp.val, env, makeSetCont(exp, env, cont)); export const makeSetCont = (exp: SetExp, env: Env, cont: Cont) => (rhsVal: Result<Value>) => bind(rhsVal, rhs => bind(applyEnvBdg(env, exp.var.var), bdg => { setFBinding(bdg, rhs); return applyCont(cont, makeOk(undefined))})); const evalApp = (exp: AppExp, env: Env, cont: Cont): Result<Value> => evalCont(exp.rator, env, (proc) => evalExps(exp.rands, env, (args) => applyProcedure(proc, args, cont))); const applyProcedure = (proc: Result<Value>, args: Result<Value[]>, cont: Cont): Result<Value> => bind(proc, (proc: Value) => bind(args, (args: Value[]) => isPrimOp(proc) ? applyCont(cont, applyPrimitive(proc, args)) : isClosure(proc) ? applyClosure(proc, args, cont) : applyCont(cont, makeFailure(`Bad procedure: ${JSON.stringify(proc, null, 2)}`)))); const applyClosure = (proc: Closure, args: Value[], cont: Cont): Result<Value> => { const vars = map((v: VarDecl) => v.var, proc.params); return evalSequence(proc.body, makeExtEnv(vars, args, proc.env), cont); } // Final continuation export const topCont: Cont = (val) => { either(val, v => console.log(valueToString(v)), console.error); return val; } // Evaluate a program // Main program export const evalProgram = (program: Program): Result<Value> => evalSequence(program.exps, theGlobalEnv, topCont); export const evalParse = (s: string): Result<Value> => bind(bind(p(s), parseL5Exp), exp => evalSequence([exp], theGlobalEnv, topCont));