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Scheme Cheat Sheet |
This is the file extension for Scheme, just like .docx is the file extension for Microsoft Word files. shudder We were using little.scm as the file to do our Scheme work.
The word for what the computer does with expressions. This can be a
process of simplification---~(+ 2 2)~ will be evaluated as 4, for
example. In the case of functions, it can mean making them available for
use.
There are three ways you can think of functions, in increasing order of correctness.
- A way to make your computer do something.
- A way to save some code for later. (Also known as a subroutine.)
- Like in math, a thing that takes an input, does something with it, and returns an output. Think of a machine with a hole in the top and a slot in the bottom.
Use a function by making an expression (stuff between parentheses) that has the function name first and then the inputs after it. Like this:
(expt 5 2)
=> 25
expt is the exponent function. The first input is the base and the
second input is the power. 5 to the power of 2. We call inputs to a
function arguments or parameters.
Geiser is just some Emacs code that lets us start and access Guile from inside Emacs.
Programming is kind of like making a house. First, you design something, then you actually build it. In programming, designs for big things like languages and protocols are called standards. The actual product of the design after it's built is the implementation. So, Scheme has a standard that defines the language in the abstract, but it also has different implementations, actual code that runs Scheme programs, that are in practice slightly different from each other. So far we're been using Guile, but there's also MIT Scheme and Chicken Scheme.
Recursion in the abstract means a thing referring to itself. In programming, it usually means calling a function from inside itself. Recursion is a useful way of solving problems and is particularly encouraged in Scheme. Scheme is associated with the introduction of tail recursion, which if implemented in a programming language allows recursion to be performed more efficiently.
See Douglas Hofstader's fun article on Lisp's lists and recursion from the book Metamagical Themas.
Open Emacs. (Finder > Emacs if you've downloaded the OSX version to your Applications folder)
Start the Scheme process. Hit alt-x. At the prompt, type
run-geiser
You'll see a prompt:
Start Geiser for scheme implementation:
Type guile at the prompt and hit enter. You should see a window appear
with your Scheme process.
Run Scheme code. You can type directly into the REPL (the Scheme process) by typing at the prompt that looks like this:
scheme@(guile-user)>
Just type some Scheme and hit Enter.
The other way to run code is to run it from a .scm file (Scheme file).
To do this, first make sure your REPL (guile process) is running. Open a
.scm file. Type some Scheme into the file, then put your cursor at the
end of an expression and type C-x C-e. The code should run and you'll
see output, if any, in the minibuffer.
Lisp was a cool math notation that someone at MIT came up with. One of his grad students looked at it and was like, "Did you know this is basically a programming language?" The guy was like, "cool." They used it for AI research until the field of AI collapsed in on itself.
As a language it's interesting because code/procedures are the same as data. In Lisp's elemental form there really is no syntax, basically just expressions that look like lists. Unimaginatively, it stands for LISt Processing.
Lisps are basically lemurs in a world of monkeys. Almost all non-lisps are descended from a language called Algol by way of a language called C. Lisps are atavistic. Lisp had a ton of great ideas that Algol-derived languages continue to adopt at a rate of one every seven years or so.
See The Lisp Curse, Paul Graham on Lisp, and Why Lisp Failed. Lisp seems to be making a comeback---it's functional and functional programming is so hot right now. Also Clojure is a trendy new Lisp. Will it ever be as popular as Algol-derived languages? No, because path dependence.
It's a programming language that someone made at MIT to teach in his programming classes. The most famous book about it is SICP. That book is really hard but I will finish it some day. Scheme is a Lisp.
Scheme is pretty cool to learn because it's intentionally small and because there are good books written for it.
Your Emacs configuration file is called .emacs and lives in your home
folder. The file consists of code that is run when Emacs starts up.
Called M-x in Emacs lingo. You type this and then type the name of a function. For example, hold alt, hit x, and then enter this in the prompt:
tetris
which runs a function that starts a game of tetris. Why tetris is included in Emacs I don't know.
Hit C-g to get out of sticky situations. Hit this key often.
M-x butterfly
Emacs Learning
Curve
See Richard Stallman.
C-f means hold down control and press f
M-f means hold down alt and press f
S-f means hold down shift and press f
C-M-f means hold down control and alt and press f
The area below the gray bar. This is where you see messages from Emacs and where you are prompted to enter information.
C-x C-f (control-x, control-f) After hitting it, you'll see a prompt in the minibuffer. If you type a filename, it will open the file. If you type a name that doesn't exist yet, it will open an empty buffer that you can type in. Once you save that buffer, a new file will be created with that name. So the open file function is also how you create new files.
Type C-h t to start the built-in tutorial. Highly recommended.
An old text editor with a lot of features. Made by a cranky person who likes parrots.
In 1997, there was a break in the community of non-proprietary software developers. Due to personality conflicts with Richard Stallman and a feeling that his stance on free software as an ethical issue was anti-business, some developers, including Eric Raymond, started the open source movement. Open source advocates for releasing code to the public as a sensible and sustainable business practice rather than an ethical requirement.
One of many programming paradigms, or high-level ways of architecting software. Though functions are used in almost all modern programming, programming in the functional style means passing values from function to function so that few variables have to be defined and so that structures in memory don't have to be changed in place. Most programmers aren't initially trained in this style but it's shown its usefulness in creating software that avoids certain classes of bugs and which allows the computer to split up problems into discrete tasks that can be run in paralell without causing trouble.
Scheme is designed as a functional programming language, though functional programming isn't enforced like in some languages like Haskell. That means you're encouraged to solve problems by passing values from function to function.
In modern usage, someone who exploits or infiltrates computer systems. Originally a term derived from the community that grew up around the MIT Model Train Club (yes, really) and the AI Lab to mean someone who deeply understood a system. Still used as a term of respect for a certain kind of programmer or as self-identification for programmers who aspire to a particular aesthetic or who work with technologies or problem domains where the hacker ethos is valued. Lisp programmers frequently refer to themselves as Lisp hackers. In other communities, the term hacker is more associated with creating quick or ad hoc solutions.
Creator of Emacs, also known as RMS. After an incident involving a recalcitrant printer, Stallman embarked on a lifelong crusade against proprietary software. His belief that free vs. proprietary software is a matter of ethics led to a schism in the community of non-proprietary software developers---see free vs. open source software.
Entrepreneur who writes a lot about Lisp. Used Lisp to create Viaweb, a web app for making online stores, and sold it to Yahoo. Created a famous (possibly the most famous) tech incubator, Y Combinator, which is named after a complicated programming technique for recurring inside an unnamed function. I think that's what a Y Combinator is, anyway.