"Cloak of Darkness".
The story headline is "A basic IF demonstration.".

use full-length room descriptions.

The maximum score is 2.
when play begins:
say "Hurrying through the rainswept
November night, you're glad to see the bright lights of the Opera House.
  It's surprising that there aren't more people about, but, hey, what do
you expect in a cheap demo game...?".

The player is wearing a velvet cloak.  The description of the cloak is
"A handsome cloak, of velvet trimmed with satin, and slightly spattered
with raindrops.  Its blackness is so deep that it almost seems to suck
light from the room."

Foyer of the Opera House is a room.  "You are standing in a spacious
hall, splendidly decorated in red and gold, with glittering chandeliers
overhead.  The entrance from the street is to the north, and there are
doorways south and west."

Instead of going north in the Foyer of the Opera House, say "You've only
just arrived, and besides, the weather outside seems to be getting worse."

Instead of dropping the cloak in the Foyer of the Opera House, say "This
isn't the best place to leave a smart cloak lying around."

Before going to the Foyer bar: if the player has the velvet cloak, now
the Foyer bar is dark; otherwise now the foyer is lighted; continue the
action.

The Cloakroom is west of the Foyer.  "The walls of this small room were
clearly once lined with hooks, though now only one remains.  The exit is
a door to the east."

A small brass hook is here. the hook is scenery and a supporter.

understand the command "hang" as something new.
hanging is an action applying to two things.
understand "hang [something] on [something] " as hanging.
instead of  hanging the cloak:
try putting the cloak on the hook.

After putting the cloak on the hook for the first time: increase score
by 1; continue the action.

The Foyer bar is a room.  The foyer bar is south of the Foyer of the
Opera House.  "The bar, much rougher than you'd have guessed after the
opulence of the foyer to the north, is completely empty.  There seems to
be some sort of message scrawled in the sawdust on the floor."

Before going to the Foyer bar: if the player carries the velvet cloak,
now the Foyer bar is dark; continue the action.

The disturbance factor is a number variable.  The disturbance factor is 0.

Instead of doing something other than going in the bar when the Foyer
bar is dark:
        If the location is the Foyer bar begin;
                say "In the dark? You could easily disturb something!";
                increase the disturbance factor by 1;
        otherwise;
                 continue the action;
        end if.

A message is here.  Understand "sawdust" as the message.  The message is
scenery.
Instead of examining the message:
        If the disturbance factor is less than 2 begin;
                increase the score by 1;                
                say "The message, neatly marked in the sawdust, reads...";
                end the game in victory;
        otherwise;
                increase the score by 1;
                say "The message has been carelessly trampled, making it difficult to
read.  You can just distinguish the words...";
                end the game saying "You have lost";
        end if.