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Looking Around in our Game World
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The first command we'd want to have is one that tells us
about the location we're standing in. So what would a function
need to describe a location in a world? Well, it would need to
know the location we want to describe and be able to look at a
map and find that location on the map. Here's our function, and
it does exactly that:
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(defun describe-location (location map)
(second (assoc location map)))
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The word defun means, as you might expect, that we're
defining a function. The name of the function is
describe-location and it takes two parameters: a location
and a map. These variables are local parameters of a function
and hence unrelated to the global location
and map variables. Note that functions in
Lisp are often more like functions in math than in other
programming languages: If you can remember back to your
pre-algebra class, a math function is just a relationship
between a bunch of inputs (called the domain) to an output
(called the range.) In math, you would never have a function
that pops up a message box or prints stuff for the user to read -
Our function describe-location is a lot like that, because
it is a function that just calculates a value (in this case, the
description of a location on our map.) Let's imagine our
location is in the living-room (which, indeed, it is...)
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