Package gnu.mapping

Class 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 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 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​(Consumer out)  
      void print​(java.lang.Appendable 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