File content as of revision 2:23bd19542152:

#include "mbed.h"

void sw1TimeOutHandler();
void sw1RisingEdge();
void sw1FallingEdge();

#define EDGE_RISEN 1
#define EDGE_FALLEN 0

//Global Objects
DigitalOut  led(LED1);
InterruptIn   sw1(USER_BUTTON);
Timeout sw1TimeOut;             //Used to prevent switch bounce
int sw1State = EDGE_FALLEN;     //Initial state for switch 1

//Interrupt service routine for handling the timeout
void sw1TimeOutHandler() {
    //Which event does this follow?
    switch (sw1State) {
    case EDGE_RISEN:    
        sw1.fall(&sw1FallingEdge);  //Now wait for a falling edge
        break;
    case EDGE_FALLEN:
        sw1.rise(&sw1RisingEdge);   //Now wait for a rising edge
        break;
    } //end switch 
}

//Interrupt service routine for a rising edge (press)
void sw1RisingEdge() {
    sw1.rise(NULL);             //Disable detecting more rising edges
    sw1State = EDGE_RISEN;      //Flag state
}

//Interrupt service routive for SW1 falling edge (release)
void sw1FallingEdge() {
    sw1.fall(NULL);                         //Disable this interrupt
    led = !led;                             //Toggle LED    
    sw1State = EDGE_FALLEN;                 //Flag state
}

//Main - only has to initialise and sleep
int main() {
    //Initial logging message
    puts("START");
    
    //Configure interrupts, wait for first rising edge
    sw1.rise(&sw1RisingEdge);
    
    //Main Polling Loop
    while (true) {
        //Set LED to OFF
        led    = 0; 
        
        //Put CPU back to sleep
        sleep(); //woken by rising edge
        puts("Rising");
        wait(0.2);
        sw1TimeOutHandler();
        sleep(); //Falling edge
        puts("Falling");
        wait(0.2);
        sw1TimeOutHandler();
        
        //You can ONLY reach this point if an ISR wakes the CPU
        for (int n=0; n<10; n++) {
            led = !led;
            wait(0.1);
        }
        
    } //end while

}