Well, first of all, it would *really* help if you formatted your code,
because currently your code is almost impossible to read.
Let's format it first:
(defn simplify-string [original substring replacement]
(let [simplified (str/replace original substring replacement)]
simplified))
(defn simplify-dat-guy [exp]
(loop [[k v] translations exp exp]
(recur [k v] (simplify-string exp k v))))
(defn completely-simplify-dat-guy [exp]
(loop [exp exp]
(cond
(= (.length exp) 1) exp
(second-condition exp) (recur (simplify-dat-guy exp)))))
We can simplify this a little further still by removing simplify-string,
since it's just a wrapper around str/replace:
(defn simplify-dat-guy [exp]
(loop [[k v] translations exp exp]
(recur [k v] (str/replace exp k v))))
And since recur works with functions, we can also remove the outer loop:
(defn completely-simplify-dat-guy [exp]
(cond
(= (.length exp) 1) exp
(second-condition exp) (recur (simplify-dat-guy exp)))))
The loop in "simplify-dat-guy" is also an example of a fold over a map, so
we can replace it with reduce-kv:
(defn simplify-dat-guy [exp]
(reduce-kv str/replace exp translations))
Now let's look at your problem. Assuming I've understood correctly, you
want to simplify until you have a string of length 1, or a string that
cannot be reduced any further?
So in that case, something like:
(defn simplify [expr translations]
(if (= (count expr) 1)
expr
(let [next-expr (reduce-kv str/replace expr translations)]
(if (< (count next-expr) (count expr)
(recur next-expr)))))
If we cannot reduce the expression, rather than returning "-1", let's just
return nil instead.
- James
On 23 November 2014 at 16:25, Dan Campbell <[email protected]> wrote:
> Hi,
>
> I have to loop through a string, consecutively replacing substrings with
> single characters, one substring at a time. Each time through the loop, I
> need to use a cond to check that the length of the last replaced string, is
> shorter than the length of the previous replaced string.
>
> So, as an artificial example, say you have a string "1001110011011", and a
> map or vector of substrings and replacements
>
> ( def map_translations
> {
> { "00" "0" },
> { "01" "0" },
> { "10" "0" },
> { "11" "1" }
> }
>
> ( The resemblance to a conjunction truth table is coincidental. This is
> the simplest example I could think of. )
>
>
> So I want to loop through the map of translations several times, each time
> trying to simplify the original expression further, until a result of
> either "-1" or a single character is returned.
>
> If the length of the replaced string is greater than or equal to the
> length of the last replacement, then I'd want to return a "-1" string.
>
> But I can't figure out, how to compare the length of a result of a recur
> assignment, to the length of the PREVIOUS recur assignment.
>
>
> So, it might look something like this (untested):
>
>
>
> ( defn simplify-string
> [ s_original-string s_substring s_replacement-character ]
> (
> let [ s_simplified-string ( clojure.string/replace s_original-string
> s_substring s_replacement-character ) ]
> s_simplified-string
> )
> )
>
>
> ( defn simplify-dat-guy
> "Loops through a map of substring to character translations,
> attempting to simplify a given expression.
> e.g., '00101' through successive translations would become a shorter
> form
> "
> [ s_exp ]
> ( loop
> [ [k v] map_longform-shortform-translation s_simplified-expression
> s_exp ]
> ( recur [ k v ] ( simplify-string s_simplified-expression k v ) )
> )
> )
>
>
> ( defn completely-simplify-dat-guy
> "Loops through simplify-dat-guy several times,
> until either a single character or a "-1" is returned.
> e.g., '00101' through successive simplify-dat-guys would eventually
> become "0".
> "
> [ s_exp ]
> ( loop
> [ s_simplified-expression s_exp ]
> (
> cond
> ( = ( .length s_simplified-expression ) 1 )
> s_simplified-expression
> ( comment
> I want to put a second condition in here, something like
> ( = ( .length s_simplified-expression ) ( .length
> PREVIOUS_s_simplified_expression ) )
> "-1"
> )
> ( recur ( simplify-dat-guy s_simplified-expression ) )
> )
> )
> )
>
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