The Seasoned Schemer 026256100X, 9780262561006
Table of contents : Cover......Page 1 Contents......Page 2 Foreword......Page 3 Preface......Page 4 11. Welcome Back to
113 16 11MB
English Pages 216 Year 1996
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- Author / Uploaded
- Daniel P. Friedman
- Matthias Felleisen
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Citation preview
There is no answer for
x2
Yes , X2 is an imaginary name just as . . Imagmary name.
Do omnivore and gobbler observe The Sixteenth Commandment?
They do. The name in (set! . . . ) is introduced by a (let ...) .
What is the value of nibbler
Unimaginable. Keep reading.
Xl
is an
.
. (define nibbler (lambda (food) (let ((x (quote donut) ) ) (set! x food) (cons food (cons x (quote 0))))))
\iVhat is the value of (nibbler (quote cheerio) )
(cheerio cheerio) .
Does nibbler still know about cheerio
No!
How do we determine the value of (nibbler (quote cheerio) )
First, we determine the value of (quote don ut), which is easy. And then we give it a name: x .
And second?
Second, we change what cheerio.
And third?
Third, we determine the value of (cons food (cons x (quote 0))) where x is cheerio and food is cheerio.
100
x
stands for to
Chapter 15
So ,,"hat was t hc use of (let" " " )
one" If (let" " ) and (set! ) ar \ l ret without a (lambda" b tW,('ll them, th don't h lp us to remember things. "
"
"
"
"
"
.v
Because there is no (lambda bet\\"eCll the (let ( ( x " ) ) "" . ) and t he (set! x " . " ) in (lambda (food)
So why is it unimaginable?
"
"
(let ( ( x (quote don ut ) ) ) (set! x food) ) )" "
"
The Seventeenth Commandment
Use (set!
x
(preliminary version) ) for (let (( )) x ...
...
there is at least one (lambda ... and the (let
((
x ...
))
.
.
.
)
.
.
.
)
only if
between it
.
Isn't (let ...) like (letrec ... )
Yes , we said it was similar.
Do you think The Sixteenth and Seventeenth Commandments also apply to names in the name part of (letrec ... )
Yes, they do, and we will see examples of t his, but not just yet.
Why did we forget The Sixteenth Commandment earlier?
Occasionally we need to ignore commandments, because it helps to explain things.
The Dife f rence Between
fen and BOJ"
10 1
!1G)� ru�� � �c �
"
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,
o ,
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