Greetings,
I'm working through HtDP alone and am currently stuck. All the relevant code
can be found here:
https://gist.github.com/simalaia/d5b50e9a0bd36b89128aecb43de71cf8
As suggested in the book I start with (insert-everywhere/in-all-words) and
design a new function with signature 1String Word -> List-of-Words and the
purpose statement "insert 1String into every position of Word", I get stuck
here.
I used the table method to try and work out what the next function I need to
design is, however everything I try results in me coming up with needing
exactly the function that I started with, along with the problem that I started
with.
Every attempt at directly solving it (but see below on how this 'solving' is
being done) without an auxiliary function results in some tests failing. For
example (f "x" (list "a")) -> (("x" "a") ("a" "x")) but this fails when given
length zero or two words. I have not managed any improvements on this.
There seems to be a fairly obvious solution along the lines of (map append
(prefixes w) (map (λ (x) (cons s x)) (suffixes w))) however that seems to
require the simultaneous processing chapter and is based more on intuition than
design. I am, either way, not asking as to the solution for this problem.
What I can't work out is where my understanding of the design recipe is
failing? The implementation I have so far is based on my extrapolation from
the list-of-lists recipe to how trees would likely be processed and based on a
pure intuitive guess rather than systematic application of the recipe. The
table method also doesn't seem to be producing any results that I understand.
Nor are the tests helping...
Hence, could someone assist with debugging my understanding of the recipe?
Regards.
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