Class Task

constructor

• new Task(
      priority: number,
      scheduler: Scheduler,
      code: Thing,
      env: Thing<env> | Thing<nil>,
  ): Task

  Parameters

  • priority: number
  • scheduler: Scheduler
  • code: Thing
  • env: Thing<env> | Thing<nil>

  Returns Task

priority

result

scheduler

stack

suspended

continuation

• continuation(loc?: LocationTrace): Thing<continuation>

  Return a new thing representing the current continuation at this point in evaluation, which when called will return to this point with the given value as the result of the current expression.

  The continuation will capture the entire stack, so it has infinite extent.

  Parameters

  • loc: LocationTrace = UNKNOWN_LOCATION

  Returns Thing<continuation>

dip

• dip(depth: number, cb: (state: StackEntry) => void): void

  Temporarily pop the given number of stack frames, call the callback with the new top of the stack, and then restore the popped stack frames. This is used for things like variable declaration and assignment where we need to access the correct environment to put the variable in.

  If depth is greater than or equal to the current stack size, the callback will be called with the bottom of the stack (which is usually the global scope).

  Parameters

  • depth: number
  • cb: (state: StackEntry) => void

  Returns void

enter

• enter(
      code: Thing,
      loc: LocationTrace,
      env: Thing<env> | Thing<nil>,
      args?: readonly Thing<string | ThingType>[],
      name?: string | null,
  ): void

  Enters a new stack frame with the given code, location, environment, and arguments.

  Parameters

  • code: Thing
  • loc: LocationTrace

    The location trace to use in error messages.

  • env: Thing<env> | Thing<nil>
  • args: readonly Thing<string | ThingType>[] = []
  • Optionalname: string | null

    The name of the stack frame, if it is significant and should appear in a stack trace.

  Returns void

out

• out(result?: Thing<string | ThingType>): StackEntry

  Exit the current stack frame, optionally with a result to return to the caller. The result will be passed back to whatever got us here (e.g. the parent stack frame or the creator of the task).

  Parameters

  • Optionalresult: Thing<string | ThingType>

  Returns StackEntry

step

• step(): boolean

  Try to take a single evaluation step in this task. Returns true if the task made progress (e.g. evaluated something or updated its state), or false if the task is currently suspended or has finished execution. If the task throws an error during evaluation, the task may end up in an undefined state.

  Returns boolean

updateArgs

• updateArgs(args: Thing<string | ThingType>[]): StackEntry

  Update the current stack entry with new arguments, returning the new stack entry.

  Parameters

  • args: Thing<string | ThingType>[]

  Returns StackEntry

updateCookie

• updateCookie(index: number, state: number, data?: any): StackEntry

  Update the current stack entry with a new cookie value(s), returning the new stack entry. The cookie is used to track internal evaluation state for constructs that call back into Backolon code, so the Javascript implementation knows where it was and can resume evaluation from the correct point when the Backolon code returns.

  The exact meaning of the cookie value(s) depends on the construct being evaluated.

  Parameters

  • index: number
  • state: number
  • Optionaldata: any

    An optional additional data to store in the stack entry, which won't be updated if not provided.

  Returns StackEntry

updateEnv

• updateEnv(newEnv: Thing<env>): StackEntry

  Updates the current stack entry with a new environment, returning the new stack entry. This is used when entering a new scope (e.g. injecting context-sensitive information).

  Parameters

  • newEnv: Thing<env>

  Returns StackEntry

updateFlags

• updateFlags(toSet: number, toClear: number): StackEntry

  Updates the current stack entry with new flags, returning the new stack entry. toSet and toClear are bitmasks of StackFlag values to set and clear respectively.

  Parameters

  • toSet: number
  • toClear: number

  Returns StackEntry