6.001 Recitation #7 – Feb 26, 2003

RI: Konrad Tollmar

Program methodology

The MIT Scheme debugger

Catch-up

1. Prog practice

1. Layout
2. Documenting
3. Debug
4. Test case
5. Types (number?, string?, Boolean?, List?, Pair? )

2. Errors

1. Common Sources of (Scheme) Errors
2. Scheme Error Messages
3. MIT Scheme Debugging Tools
4. Debugging Strategy

3. Let

Use let to write a procedure that compute

a = 1 + xy; b = 1 - y; f(x,y) = a²x + by + ab

4. Eval some list procedures.

x => (())

y => (1 2 3)

z => (1 (2 3) ((4)))

w => (1 2 3 4 5)

(map (lambda (x) (cons x nil)) y)

(map inc w)

(filter odd? w)

(map inc (filter odd? w))

(filter odd? (map inc w))

(accumulate + 0 (map inc (filter odd? w)))

5. What are the types of these procedures?

1. length

2. list-ref

3. map

4. filter 5. accumulate

6. More higher-order procedures.

Write a function comp that takes two arguments a and b and returns a function, that when called with #t returns a and when called with #f returns b.