[Edu-sig] recent curriculum writing (Urner)
kirby.urner at gmail.com
Thu Oct 8 22:36:57 CEST 2009
What do we mean by "computer language"? One could answer in terms of
using text to control electronics, and that would be accurate.
However there's also the goal of a philosophical logic: to express
situations in the world, to mirror them for the purposes of
The veteran programmer of the late 1900s experienced a number of
twists and turns in the art of computer programming. This field has
evolved quickly. Early machines had to be programmed "close to the
metal" meaning a deep understanding of hardware internals was needed
to even begin to write code.
Today's computer languages haven't completely divorced themselves from
hardware concerns, but the higher level ones are freer to concentrate
on what we sometimes call "knowledge domains" such as cellular
automata, molecular biology, zoology, telescopy etc.
When talking about human languages, we have something we call grammar.
It helps to know the difference between a verb and an adjective, an
adjective and a noun. In many of today's computer languages, nouns
name objects which have attributes (like adjectives) and behaviors
Here's an idea of what computer code might look like:
anAnt = Ant()
critter = AntEater()
critter.color = 'brown'
If you've studied some mathematics, you may be used to reading "=" as
"equals". You're free to keep doing that, but add the thought that
"=" is an "assignment operator" and what it does is bind a name to an
In the above segment of code, the Ant and AntEater types are
instantiated and assigned to names. These names are then operated
upon using "dot notation" such that attributes get set and behaviors
such as eating invoked.
Notice that we already have a tendency to think in terms of things (a
very generic statement). Think of an airport. What "things" do you
suppose it would have? Runways and taxiways would define paths for
the airplanes. There might be a control tower. Lots of things have
come to mind already.
A single airplane has many attributes and behaviors.
pdx = Airport()
nw = Runway()
myplane = Gulfstream()
We also have an engrained concept of the more general versus the more
specific. There's the generic idea of a house, animal, airport. Then
we get more specific, getting to some individual instance of example
of any of these types of object.
A computer language might have this same idea: there's a type of
thing called a Number, and then we have individual instances of
Number, such as 3, -1 or 2.12 or whatever.
Suppose you had a generic blueprint for a robot dog. You could create
an instance of this blueprint at any time, and then modify the
specifics to give yourself an individual dog. Each "instance" would
take up its own place in memory, even though the blueprint is shared
among all these instances.
Imagine a snake named Selma, maybe a cute cartoon snake. She has a
sister named Bella. Creating these two snakes from the Snake template
might look like this:
selma = Snake()
bella = Snake()
At this point, all that differentiates these two snakes are their
names. Two snake objects have been born, and assigned to names. Now
we might modify each snake separately:
selma.color = 'red and brown stripes'
bella.color = 'various shades of gray'
One might eat a mouse, the other might eat a cupcake:
Notice our "dot notation" has so far mostly followed these grammatical patterns:
noun = Type()
noun.adjective = value
It maybe help to think of open-close parentheses as a "mouth". Think
of emoticons like :-) or :-(). The () is clearly a mouth. A mouth
eats or takes in. We call often call the things a mouth eats its
An event such as noun = Type() is akin to the birth of a creature or
instance from its generic type.
Then we make our noun do things or define its attributes, with
noun.verb(arguments) or noun.adjective = value. Also, we don't just
set attributes (store them), but we also get them (retrieve them).
What's important to realize about the above quick run through is we've
nowhere had to discuss the internals of a computer or how it works.
Writing scripts will require naming our actors and defining their
behaviors, their interactions. Writing a program is a lot like
scripting for theater.
We need to know how to express ourselves grammatically in a computer
language. But that's the same with ordinary human languages, so this
need shouldn't seem too alien or unfamiliar.
Now, the grammar suggested above is characteristic of several computer
languages, but certainly not all of them. Given we're heading into a
study of the Python computer language, all of the above is apropos
This way of thinking, using dot notation, will also serve you when
should you choose to develop your skills in any of these directions.
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