feat: goroutines (#19)

* feat: naive time quanta based scheduler

Abstracted the current program as a `main` go routine in preparation for
`GoStatement` implementation

* chore: fix eslint errors

* refactor: use `Counter` for frame id generation

* refactor: add `GoStatement` to ECE types

* feat: implement `GoStatement` support in ECE

Right now we only support non-builtin calls to spawn a goroutine. We
need to consider if its even worth it spawn a new goroutine for a
builtin since its only a "1 step/tick" op. Additionally, I introduced
`GoRoutineOp` to handle spawning of new goroutines. Its payload is
same as `CallOp` so we can consider combining them if there is no
special cases to handle later on

* feat: add `StringLit` support in parser

This is mainly so that we can `println` strings to differentiate between
goroutines. Note that this is purely a convenience feature, the ECE does
not allocate strings in the heap/string pool right now.

* feat: implement `GoRoutineOp` support in heap

* feat: randomize goroutine time quanta

src/go-slang/ece.ts

@@ -1,68 +1,19 @@
 import { Context as SlangContext } from '..'
 import { Stack } from '../cse-machine/utils'
-import { RuntimeSourceError } from '../errors/runtimeSourceError'
 import { Value } from '../types'
-import { FuncArityError, UndefinedError, UnknownInstructionError } from './error'
+import { Context, GoRoutine } from './goroutine'
 import { AstMap } from './lib/astMap'
-import { evaluateBinaryOp } from './lib/binaryOp'
 import { Environment } from './lib/env'
 import { Heap, HeapAddress } from './lib/heap'
 import { PREDECLARED_FUNCTIONS, PREDECLARED_IDENTIFIERS } from './lib/predeclared'
-import { zip, isAny } from './lib/utils'
-import {
-  AssignOp,
-  Assignment,
-  BinaryExpression,
-  BinaryOp,
-  Block,
-  BranchOp,
-  BuiltinOp,
-  CallExpression,
-  CallOp,
-  ClosureOp,
-  CommandType,
-  EmptyStmt,
-  EnvOp,
-  ExpressionStatement,
-  ForEndMarker,
-  ForFormType,
-  ForPostMarker,
-  ForStartMarker,
-  ForStatement,
-  FunctionDeclaration,
-  Identifier,
-  IfStatement,
-  Instruction,
-  Literal,
-  NodeType,
-  Operator,
-  PopS,
-  PopTillM,
-  PopTillMOp,
-  RetMarker,
-  ReturnStatement,
-  SourceFile,
-  True,
-  UnaryExpression,
-  UnaryOp,
-  VarDeclOp,
-  VariableDeclaration
-} from './types'
-
-type Control = Stack<Instruction | HeapAddress>
-type Stash = Stack<HeapAddress>
-type Builtins = Map<number, (...args: any[]) => any>
-
-interface Context {
-  C: Control
-  S: Stash
-  E: Environment
-  B: Builtins
-  H: Heap
-  A: AstMap
-}
-
-export function evaluate(program: SourceFile, slangContext: SlangContext): Value {
+import { Scheduler } from './scheduler'
+import { BuiltinOp, CallExpression, Instruction, NodeType, SourceFile } from './types'
+
+function initMainGoRoutine(
+  program: SourceFile,
+  slangContext: SlangContext,
+  scheduler: Scheduler
+): GoRoutine {
   const C = new Stack<Instruction | HeapAddress>()
   const S = new Stack<any>()
   const E = new Environment({ ...PREDECLARED_IDENTIFIERS })
@@ -86,192 +37,23 @@ export function evaluate(program: SourceFile, slangContext: SlangContext): Value
     B.set(id, func)
   })
 
-  const Context = { C, S, E, B, H, A }
-
-  // start the program by calling `main`
+  // seed the `main` go routine with the program's `main` function
   const CALL_MAIN: CallExpression = {
     type: NodeType.CallExpression,
     callee: { type: NodeType.Identifier, name: 'main' },
     args: []
   }
   C.pushR(H.alloc(program), H.alloc(CALL_MAIN))
 
-  while (!C.isEmpty()) {
-    const inst = H.resolve(C.pop()) as Instruction
-
-    if (!interpreter.hasOwnProperty(inst.type)) {
-      slangContext.errors.push(new UnknownInstructionError(inst.type))
-      return undefined
-    }
-
-    const runtimeError = interpreter[inst.type](inst, Context)
-    if (runtimeError) {
-      slangContext.errors.push(runtimeError as RuntimeSourceError)
-      return undefined
-    }
-  }
-
-  return 'Program exited'
+  return new GoRoutine({ C, S, E, B, H, A } as Context, scheduler, true)
 }
 
-const interpreter: {
-  [key: string]: (inst: Instruction, context: Context) => RuntimeSourceError | void
-} = {
-  SourceFile: ({ topLevelDecls }: SourceFile, { C, H }) => C.pushR(...H.allocM(topLevelDecls)),
-
-  FunctionDeclaration: (funcDeclNode: FunctionDeclaration, { E, A }) => {
-    const { id, uid: funcDeclNodeUid } = funcDeclNode
-    A.set(funcDeclNodeUid as number, funcDeclNode)
-    E.declare(id.name, { type: CommandType.ClosureOp, funcDeclNodeUid, envId: E.id() } as ClosureOp)
-  },
-
-  Block: ({ statements }: Block, { C, E, H }) => {
-    C.pushR(...H.allocM([...statements, { type: CommandType.EnvOp, envId: E.id() }]))
-    E.extend({})
-  },
-
-  ReturnStatement: ({ expression }: ReturnStatement, { C, H }) =>
-    C.pushR(H.alloc(expression), H.alloc(PopTillM(RetMarker))),
-
-  IfStatement: ({ stmt, cond, cons, alt }: IfStatement, { C, H }) => {
-    const branchOp: BranchOp = { type: CommandType.BranchOp, cons, alt }
-    stmt ? C.pushR(...H.allocM([stmt, cond, branchOp])) : C.pushR(...H.allocM([cond, branchOp]))
-  },
-
-  ForStatement: (inst: ForStatement, { C, H }) => {
-    const { form, block: forBlock } = inst
-    if (form === null || form.type === ForFormType.ForCondition) {
-      const branch = { type: CommandType.BranchOp, cons: forBlock, alt: PopTillM(ForEndMarker) }
-      C.pushR(
-        ...H.allocM([
-          form ? form.expression : True,
-          branch as BranchOp,
-          ForStartMarker,
-          inst,
-          ForEndMarker
-        ])
-      )
-    } else if (form.type === ForFormType.ForClause) {
-      const { init, cond, post } = form
-      const forCond = {
-        type: NodeType.ForStatement,
-        form: { type: ForFormType.ForCondition, expression: cond ?? True },
-        block: {
-          type: NodeType.Block,
-          statements: [
-            { ...forBlock, statements: forBlock.statements.concat(ForPostMarker) },
-            post ?? EmptyStmt
-          ]
-        }
-      } as ForStatement
-      C.push(H.alloc({ type: NodeType.Block, statements: [init ?? EmptyStmt, forCond] }))
-    }
-  },
-
-  BreakStatement: (_inst, { C, H }) => C.push(H.alloc(PopTillM(ForEndMarker))),
-
-  ContinueStatement: (_inst, { C, H }) => C.push(H.alloc(PopTillM(ForPostMarker, ForStartMarker))),
-
-  VariableDeclaration: ({ left, right }: VariableDeclaration, { C, H, A }) => {
-    const decls = A.trackM(left).map(({ uid }) => ({ type: CommandType.VarDeclOp, idNodeUid: uid }))
-    return right.length === 0
-      ? // if there is no right side, we push zero value for each declaration
-        C.pushR(...H.allocM(decls.map(decl => ({ ...decl, zeroValue: true }))))
-      : // assume: left.length === right.length
-        C.pushR(...H.allocM(right), ...H.allocM(decls.reverse()))
-  },
-
-  Assignment: ({ left, right }: Assignment, { C, H, A }) => {
-    const ids = left as Identifier[] // assume: left is always an array of identifiers
-    const asgmts = ids.map(id => ({ type: CommandType.AssignOp, idNodeUid: A.track(id).uid }))
-    C.pushR(...H.allocM(right), ...H.allocM(asgmts.reverse()))
-  },
-
-  EmptyStatement: () => void {},
-
-  Literal: (inst: Literal, { S, H }) => S.push(H.alloc(inst.value)),
-
-  Identifier: ({ name }: Identifier, { S, E, H }) => {
-    const value = E.lookup(name)
-    return value === null ? new UndefinedError(name) : S.push(H.alloc(value))
-  },
-
-  UnaryExpression: ({ argument, operator: op }: UnaryExpression, { C, H, A }) =>
-    C.pushR(...H.allocM([argument, { type: CommandType.UnaryOp, opNodeId: A.track(op).uid }])),
-
-  BinaryExpression: ({ left, right, operator: op }: BinaryExpression, { C, H, A }) =>
-    C.pushR(...H.allocM([left, right, { type: CommandType.BinaryOp, opNodeId: A.track(op).uid }])),
-
-  CallExpression: ({ callee, args }: CallExpression, { C, H, A }) =>
-    C.pushR(
-      ...H.allocM([
-        callee,
-        ...args,
-        { type: CommandType.CallOp, calleeNodeId: A.track(callee).uid, arity: args.length }
-      ])
-    ),
-
-  ExpressionStatement: ({ expression }: ExpressionStatement, { C, H }) =>
-    C.pushR(...H.allocM([expression, PopS])),
-
-  VarDeclOp: ({ idNodeUid, zeroValue }: VarDeclOp, { S, E, H, A }) => {
-    const name = A.get<Identifier>(idNodeUid).name
-    zeroValue ? E.declareZeroValue(name) : E.declare(name, H.resolve(S.pop()))
-  },
-
-  AssignOp: ({ idNodeUid }: AssignOp, { S, E, H, A }) => {
-    const name = A.get<Identifier>(idNodeUid).name
-    !E.assign(name, H.resolve(S.pop())) ? new UndefinedError(name) : void {}
-  },
-
-  UnaryOp: ({ opNodeId }: UnaryOp, { S, H, A }) => {
-    const operand = H.resolve(S.pop())
-    S.push(H.alloc(A.get<Operator>(opNodeId).op === '-' ? -operand : operand))
-  },
-
-  BinaryOp: ({ opNodeId }: BinaryOp, { S, H, A }) => {
-    const [left, right] = H.resolveM(S.popNR(2))
-    S.push(H.alloc(evaluateBinaryOp(A.get<Operator>(opNodeId).op, left, right)))
-  },
-
-  CallOp: ({ calleeNodeId, arity }: CallOp, { C, S, E, B, H, A }) => {
-    const values = H.resolveM(S.popNR(arity))
-    const op = H.resolve(S.pop()) as ClosureOp | BuiltinOp
-
-    // handle BuiltinOp
-    if (op.type === CommandType.BuiltinOp) {
-      return S.push(H.alloc(B.get(op.id)!(...values)))
-    }
-
-    // handle ClosureOp
-    const { funcDeclNodeUid, envId } = op
-    const { params, body } = A.get<FunctionDeclaration>(funcDeclNodeUid)
-    const paramNames = params.map(({ name }) => name)
-
-    if (paramNames.length !== values.length) {
-      const calleeId = A.get<Identifier>(calleeNodeId)
-      return new FuncArityError(calleeId.name, values.length, params.length)
-    }
-
-    C.pushR(...H.allocM([body, RetMarker, { type: CommandType.EnvOp, envId: E.id() }]))
-    // set the environment to the closure's environment
-    E.setId(envId).extend(Object.fromEntries(zip(paramNames, values)))
-  },
-
-  BranchOp: ({ cons, alt }: BranchOp, { S, C, H }) =>
-    void (H.resolve(S.pop()) ? C.pushR(H.alloc(cons)) : alt && C.pushR(H.alloc(alt))),
-
-  EnvOp: ({ envId }: EnvOp, { E }) => void E.setId(envId),
-
-  PopSOp: (_inst, { S }) => void S.pop(),
-
-  PopTillMOp: ({ markers }: PopTillMOp, { C }) => {
-    while (!C.isEmpty() && !isAny(C.pop(), markers)) {}
-  },
+export function evaluate(program: SourceFile, slangContext: SlangContext): Value {
+  const scheduler = new Scheduler(slangContext)
+  const mainR = initMainGoRoutine(program, slangContext, scheduler)
 
-  RetMarker: () => void {},
+  scheduler.schedule(mainR)
+  scheduler.run()
 
-  ForStartMarker: () => void {},
-  ForPostMarker: () => void {},
-  ForEndMarker: () => void {}
+  return 'Program exited'
 }

src/go-slang/error.ts

@@ -50,3 +50,16 @@ export class FuncArityError extends RuntimeSourceError {
     )
   }
 }
+
+export class GoExprMustBeFunctionError extends RuntimeSourceError {
+  private expr: string
+
+  constructor(expr: string) {
+    super()
+    this.expr = expr
+  }
+
+  public explain() {
+    return `expression in go statement must be function call, not ${this.expr}`
+  }
+}