Held: Friday, February 3, 2006
Summary:
Today we explore some of the reasons that functional programming is
a particularly powerful paradigm.
Related Pages:
Assignments
- Using Graham's example, implement a simple LISP that includes lambdas, defines, and lets. You should start with
cons, car, cdr,
nil, null? eval, cond, quote, atom?, eq?. For a C, use Scheme as your implementation language (that is, you need not implement these basic operations). For a B, use Java or C (that is, you'll need to implement the basic operations first). For an A, add input and output. Due next Friday.
Notes:
- Slight changes to schedule. No reading for Monday.
- I'm trying something a little different today.
Overview:
- Why LISP?
- Higher-order functions, revisited.
- Notes on the readings.
- Graham presents nine key ideas from LISP.
- How important do you consider each of these?
- How would Wirth and Hoare react to each?
- Are they all equal in importance?
- Conditionals.
- Functions as first-class data.
- Recursion.
- Dynamic Typing.
- Garbage Collection.
- Unification of expression and statement.
- Symbols as first-classs data.
A notation for code using trees of symbols and constants.
The whole language there all the time.
- We may also wish to contrast them with McCarthy's list of key ideas.
- Computing with symbolic expressions.
- Representation of data by list structures in memory.
- External representation by multi-level lists and S-expressions.
- A small set of selectors.
- Composition of functions as a tool.
- Conditional expressions.
- Recursion.
- Lambda expression.
- LISP programs are LISP data.
eval.- Garbage collection.
- One particularly powerful aspect of functional programming is the
so-called higher-order functions (that is, functions that take
functions as parameters or return functions as values).
- For example,
-
map
-
section
-
compose
- ...
- Why are these so important?
- They lead to more concise code.
- The provide an elegant way of extracting control.
- We'll consider these issues in the context of some simple graphics
functions.
- What were the most surprising things you found from McCarthy?
- Do you accept Graham's claim that shorter code is better?
- Graham argues strongly for the power of Lisp. So, why isn't it
more popular?
;
Check with Bobby