[lambda.git] / index.mdwn

# Seminar in Semantics / Philosophy of Language #

or: **What Philosophers and Linguists Can Learn From Theoretical Computer Science But Didn't Know To Ask**

This course is co-taught by [Chris Barker](http://homepages.nyu.edu/~cb125/) and [Jim Pryor](http://www.jimpryor.net/). Linguistics calls it "LING-GA 3340" and Philosophy calls it "PHIL-GA 2296".
The seminar meets in spring 2015 on Thursdays from 4 until a bit before 7 (with a short break in the middle), in 
the Linguistics building at 10 Washington Place, in room 103 (front of the first floor).

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One student session will be held every Wednesday from 3-4 on the
fourth floor at 10 Washington Place.
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## Announcements ##

This wiki will be undergoing lots of changes throughout the semester, and particularly in these first few days as we get it set up, migrate over some of the content from the previous time
we taught this course, and iron out various technical wrinkles. Please be patient.

If you've eager to learn, though, you don't have to wait on us to be ready to serve you. You can go look at the [archived first version](http://lambda1.jimpryor.net) of this course. Just keep in mind that
the text and links there haven't been updated. And/or get started on installing the software and ordering some of the books.

As we mentioned in class, if you're following the course and would like to be emailed occasionally, send an email to <mailto:jim.pryor@nyu.edu>, saying "lambda" in the subject line. Most often, we will just post announcements to this website, rather than emailing you. But occasionally an email might be more appropriate.

As we mentioned in class, we're also going to schedule a session to discuss the weekly homeworks. If you'd like to participate in this, please complete [this Doodle poll](http://doodle.com/7xrf4w8xq4i9e5za). It asks when you are available on Tuesdays and Wednesdays.

Here is information about [[How to get the programming languages running on your computer]].


## Course Overview ##

The overarching goal of this seminar is to introduce concepts and techniques from
theoretical computer science and show how they can provide insight
into established philosophical and linguistic problems.

This is not a seminar about any particular technology or software.

Rather, it's about a variety of conceptual/logical ideas that have been
developed in computer science and that linguists and philosophers ought to
know, or may already be unknowingly trying to reinvent.

Philosphers and linguists tend to reuse the same familiar tools in
ever more (sometime spectacularly) creative ways.  But when your only
hammer is classical logic, every problem looks like modus ponens.  In
contrast, computer scientists have invested considerable ingenuity in
studying the design of their conceptual tools (among other things), and they've made much progress that we can benefit from.

"Why shouldn't I reinvent some idea X for myself? It's intellectually
rewarding!" Yes it is, but it also takes time you might have better
spent elsewhere. After all, you can get anywhere you want to go by walking, but you can
accomplish more with a combination of walking and strategic subway
rides.

More importantly, the idiosyncrasies of your particular
implementation may obscure what's fundamental to the idea you're
working with. Your implementation may be buggy in corner cases you
didn't think of; it may be incomplete and not trivial to generalize; its
connection to existing literature and neighboring issues may go
unnoticed. For all these reasons you're better off understanding the
state of the art.

The theoretical tools we'll be introducing aren't part of the diet of most
everyday programmers, but they are prominent in academic computer science,
especially in the fields of functional programming and type theory.

Of necessity, this course will lay a lot of logical groundwork. But throughout
we'll be aiming to mix that groundwork with real cases
in our home subjects where these tools can (or already do, covertly) play central roles.

Our aim for the
course is to enable you to make these tools your own; to have enough
understanding of them to recognize them in use, use them yourself at least
in simple ways, and to be able to read more about them when appropriate.

[[More about the topics and larger themes of the course]]


## Who Can Participate? ##

The course will not presume previous experience with programming.  We
will, however, discuss concepts embodied in specific programming
languages, and we will encourage experimentation with running,
modifying, and writing computer programs.

The course will not presume lots of mathematical or logical background, either.
However, it will demand a certain amount of comfort working with such material; as a result,
it will not be especially well-suited to be a first graduate-level course
in formal semantics or philosophy of language. If you have concerns about your
background, come discuss them with us.

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This class will count as satisfying the logic requirement for Philosophy
PhD students; however if this would be your first or only serious
engagement with graduate-level formal work you should consider
carefully, and must discuss with us, (1) whether you'll be adequately
prepared for this course, and (2) whether you'd be better served by
taking a logic course (at a neighboring department, or at NYU next year)
with a more canonical syllabus.
-->

Faculty and students from outside of NYU Linguistics and Philosophy are welcome
to audit, to the extent that this coheres well with the needs of our local
students.


## Recommended Software ##

During the course, we'll be encouraging you to try out various things in Scheme
and OCaml. Occasionally we will also make remarks about Haskell. All three of these
are prominent *functional programming languages*. The term "functional" here means they have
a special concern with functions, not just that they aren't broken. But what precisely is
meant by "functional" is somewhat fuzzy and even its various precisifications take some
time to explain. We'll get clearer on this during the course. Another term used roughly the same as "functional"
is "declarative." At a first pass, "functional" or "declarative" programming is primarily focused on complex
expressions that get computationally evaluated to some (usually simpler) result. In class I gave the examples
of `1+2` (which gets evaluated in arithmetic to 3), `1+2 < 5` (which gets evaluated in arithmetic to 'true), and `1`
(which gets evaluated in arithmetic to 1). Also Google search strings, which get evaluated by Google servers to a
list of links.

The dominant contrasting class of programming languages (the great majority of what's used
in industry) are called "imperatival" languages, meaning they have more to do with following a sequence of commands (what we
called in class "side-effects", though sometimes what they're *alongside* is not that interesting, and all the focus is instead
on the effect). Programming languages like C and Python and JavaScript and so on are all of this sort.

In fact, nothing that gets marketed as a "programming language" is really completely 100% functional/declarative, and even the
imperatival languages will have purely functional fragments (they evaluate `1+2` to 3, also). So these labels are really
more about *styles* or *idioms* of programming, and languages like Scheme and OCaml and especially Haskell get called "functional languages" because
of the extent to which they emphasize, and are designed around those idioms. Even languages like Python and JavaScript are sometimes
described as "more functional" than some other languages. The language C is about as non-functional as you can get.

*       **Scheme** is one of two major dialects of *Lisp*, which is a large family
of programming languages. Scheme
is the more clean and minimalistic dialect, and is what's mostly used in
academic circles.
Scheme itself has umpteen different "implementations", which share most of
their fundamentals, but have slightly different extensions and interact with
the operating system differently. One major implementation is called Racket,
and that is what we recommend you use. If you're already using or comfortable with
another Scheme implementation, though, there's no compelling reason to switch.

        Racket stands to Scheme in something like the relation Firefox stands to HTML.

        (Wikipedia on [Lisp](http://en.wikipedia.org/wiki/Lisp_%28programming_language%29),
[Scheme](http://en.wikipedia.org/wiki/Scheme_%28programming_language%29),
and [Racket](http://en.wikipedia.org/wiki/Racket_%28programming_language%29).)

*       **Caml** is one of two major dialects of *ML*, which is another large
family of programming languages. Caml has only one active "implementation",
OCaml, developed by the INRIA academic group in France. Sometimes we may refer to Caml or ML
more generally; but you can assume that what we're talking about always works more
specifically in OCaml.

        (Wikipedia on [ML](http://en.wikipedia.org/wiki/ML_%28programming_language%29),
[Caml](http://en.wikipedia.org/wiki/Caml),
and [OCaml](http://en.wikipedia.org/wiki/OCaml).)


*       Those of you with some programming background may have encountered a third
prominent functional programming language, **Haskell**. This is also used a
lot in the academic contexts we'll be working through. Its surface syntax
differs from Caml, and there are various important things one can do in
each of Haskell and Caml that one can't (or can't as easily) do in the
other. But these languages also have a lot in common, and if you're
familiar with one of them, it's not difficult to move between it and the
other.

        (Wikipedia on [Haskell](http://en.wikipedia.org/wiki/Haskell_%28programming_language%29).)


<a name=installing></a>
[[How to get the programming languages running on your computer]]

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[[Family tree of functional programming languages]]

[[Translating between OCaml Scheme and Haskell]]

## What is Functional Programming? ##

Here's a [survey conducted at Microsoft](http://research.microsoft.com/apps/pubs/default.aspx?id=141506) asking programmers what they understand "functional programming" to be. Don't take their responses to be authoritative... this is a just a "man in the street" (seat?) poll.

Read more about the [uptake of Haskell](http://steve-yegge.blogspot.com/2010/12/haskell-researchers-announce-discovery.html) among programmers in the street.
-->

## Recommended Books ##

It's not *mandatory* to purchase these for the class. But they are good ways to get a more thorough and solid understanding of some of the more basic conceptual tools we'll be using. We especially recommend the first three of them.

*       *An Introduction to Lambda Calculi for Computer Scientists*, by Chris
Hankin, currently $18 paperback on
[Amazon](http://www.amazon.com/dp/0954300653).

*   *The Little Schemer, Fourth Edition*, by Daniel P. Friedman and Matthias
Felleisen, currently $29 paperback on [Amazon](http://www.amazon.com/exec/obidos/ASIN/0262560992).
This is a classic text introducing the gentle art of programming, using the
functional programming language Scheme. Many people love this book, but it has
an unusual dialog format that is not to everybody's taste. **Of particular
interest for this course** is the explanation of the Y combinator, available as
a free sample chapter [at the MIT Press web page for the
book](http://www.ccs.neu.edu/home/matthias/BTLS/).

*       *The Seasoned Schemer*, also by Daniel P. Friedman and Matthias Felleisen, currently $29 paperback
on [Amazon](http://www.amazon.com/Seasoned-Schemer-Daniel-P-Friedman/dp/026256100X). This is a sequel to The Little Schemer, and it focuses on mutation and continuations in Scheme. We will be covering those topics in the second half of the course.

*       *The Little MLer*, by Matthias Felleisen and Daniel P. Friedman, currently $31 paperback / $29 kindle
on [Amazon](http://www.amazon.com/Little-MLer-Matthias-Felleisen/dp/026256114X).
This covers much of the same introductory ground as The Little Schemer, but
this time in a dialect of ML. It doesn't use OCaml, the dialect we'll be working with, but instead another dialect of ML called SML. The syntactic differences between these languages is slight.
([Here's a translation manual between them](http://www.mpi-sws.org/~rossberg/sml-vs-ocaml.html).)
Still, that does add an extra layer of interpretation, and you might as well just use The Little Schemer instead. Those of you who are already more comfortable with OCaml (or with Haskell) than with Scheme might consider working through this book instead of The Little Schemer; for the rest of you, or those of you who *want* practice with Scheme, go with The Little Schemer.

*       Another good book covering the same ground as the Hankin book, but
more thoroughly, and in a more mathematical style, is *Lambda-Calculus and Combinators:
an Introduction*, by J. Roger Hindley and Jonathan P. Seldin, currently $74 hardback / $65 kindle on [Amazon](http://www.amazon.com/dp/0521898854).
This book is substantial and though it doesn't presuppose any specific mathematical background knowledge, it will be a good choice only if you're already comfortable reading advanced math textbooks.
If you choose to read both the Hankin book and this book, you'll notice the authors made some different
terminological/notational choices. At first, this makes comprehension slightly slower,
but in the long run it's helpful because it makes the arbitrariness of those choices more salient.

*       Another good book, covering some of the same ground as the Hankin, and the Hindley &amp; Seldin, but delving deeper into typed lambda calculi, is *Types and Programming Languages*, by Benjamin Pierce, currently $77 hardback / $68 kindle on [Amazon](http://www.amazon.com/dp/0262162091). This book has many examples in OCaml.


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