Promise

java.lang.Object
- gnu.mapping.Promise<T>

All Implemented Interfaces:

gnu.kawa.format.Printable, Lazy<T>
```
public class Promise<T>
extends java.lang.Object
implements gnu.kawa.format.Printable, Lazy<T>
```
Implement Scheme "promises". This is a final class, because in some cases (as required by SRFI-45) we copy the fields of one Promise from other Promise, and such copying would be dubious if either operand is a sub-class.

Constructor Summary

Constructors
Constructor and Description

Promise()
Create new "blank" Promise.

Promise(Procedure thunk)
Create a new Promise that will evaluate thunk when forced.

Constructors
Constructor and Description
`Promise()` Create new "blank" Promise.
`Promise(Procedure thunk)` Create a new Promise that will evaluate thunk when forced.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`Lazy`	`checkAlias()`
`void`	`checkBlank()`
`static Lazy<java.lang.Object>`	`coerceToLazy(java.lang.Object value)`
`static java.lang.Object`	`force(java.lang.Object arg)` Forces the argument, if needed, to a non-Lazy value.
`static java.lang.Object`	`force(java.lang.Object arg, java.lang.Class target)` If argument is Lazy, force it, unless already an instance of target.
`static java.lang.Object`	`force1(java.lang.Object arg)` Forces the argument, if needed.
`T`	`getValue()` Return the actual value.
`boolean`	`isBlank()`
`static <T> Promise<T>`	`makeBlank()`
`static <T> Lazy<T>`	`makeBoundPromise(T value)` Wrap value as a forced Promise.
`void`	`print(java.lang.Appendable out)`
`void`	`print(Consumer out)`
`void`	`setAlias(Lazy promise)` Bind promise to be an alias of another Lazy value.
`void`	`setException(java.lang.Throwable exception)` Bind this promise so forcing it throws the given exception.
`void`	`setForceValueIfPromise(boolean value)` Set whether to recursively call getValue if getValue yields a Lazy value.
`void`	`setThunk(Procedure thunk)` Bind this promise so forcing it evaluates the given procedure.
`void`	`setValue(java.lang.Object value)` Bind this promise to a given (eager) value.
`java.lang.String`	`toString()`

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - Promise
```
public Promise()
```
    Create new "blank" Promise. Calling getValue just waits until one of setValue, setAlias, setException or setThunk is invoked. One of these is typically done by some other "producer" thread.
  - Promise
```
public Promise(Procedure thunk)
```
    Create a new Promise that will evaluate thunk when forced.
- Method Detail
  - setForceValueIfPromise
```
public void setForceValueIfPromise(boolean value)
```
    Set whether to recursively call getValue if getValue yields a Lazy value.
  - makeBlank
```
public static <T> Promise<T> makeBlank()
```
  - makeBoundPromise
```
public static <T> Lazy<T> makeBoundPromise(T value)
```
    Wrap value as a forced Promise.
  - coerceToLazy
```
public static Lazy<java.lang.Object> coerceToLazy(java.lang.Object value)
```
  - getValue
```
public T getValue()
```
    Description copied from interface: Lazy
    
    Return the actual value. Note that getValue() may return this, if this object isn't actually lazy. It may also return another lazy value. Normally you should use Promise.force{val} to extra a non-lazy (eager) value.
    
    Specified by:
    
    getValue in interface Lazy<T>
  - isBlank
```
public final boolean isBlank()
```
  - checkBlank
```
public void checkBlank()
```
  - setValue
```
public void setValue(java.lang.Object value)
```
    Bind this promise to a given (eager) value.
  - setAlias
```
public void setAlias(Lazy promise)
```
    Bind promise to be an alias of another Lazy value.
  - setException
```
public void setException(java.lang.Throwable exception)
```
    Bind this promise so forcing it throws the given exception.
  - setThunk
```
public void setThunk(Procedure thunk)
```
    Bind this promise so forcing it evaluates the given procedure.
  - checkAlias
```
public Lazy checkAlias()
```
  - force1
```
public static java.lang.Object force1(java.lang.Object arg)
```
    Forces the argument, if needed. I.e. calls Lazy.getValue() once if the argument is Lazy.
  - force
```
public static java.lang.Object force(java.lang.Object arg)
```
    Forces the argument, if needed, to a non-Lazy value. I.e. calls Lazy.getValue() as many times as needed.
  - force
```
public static java.lang.Object force(java.lang.Object arg,
                                     java.lang.Class target)
```
    If argument is Lazy, force it, unless already an instance of target.
  - toString
```
public java.lang.String toString()
```
    Overrides:
    
    toString in class java.lang.Object
  - print
```
public void print(Consumer out)
```
    Specified by:
    
    print in interface gnu.kawa.format.Printable
  - print
```
public void print(java.lang.Appendable out)
           throws java.io.IOException
```
    Throws:
    
    java.io.IOException

Class Promise<T>

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

Promise

Promise

Method Detail

setForceValueIfPromise

makeBlank

makeBoundPromise

coerceToLazy

getValue

isBlank

checkBlank

setValue

setAlias

setException

setThunk

checkAlias

force1

force

force

toString

print

print