Hi Hank,
That loop/recur is still wrong because `loop` set bindings to define names
and gives initial values but `recur` does *not set bindings*, it just
provides new values.
So `recur` does not need a vector of bindings like `loop`
The pattern is as follow:
(loop [a-local-var "initial-value"]
(if (should-stop-looping? a-local-var)
(execute-last-expression a-local-var)
(recur a-new-local-var)))
In your pt8 function, you are reading your stream to many times in a loop,
if I write your pt8 function in procedural pseudo-code, this is what I get:
bfr = input-stream()
ct = string-buffer()
set loop-start // set loop point
with val, // set loop args
val = read(bfr) // set args initial value, first read
if !(val == -1) {
ct.append(char(read(bfr))) // read again! and lose previous byte!!
goto loop-start
with val = vector(val, read(bfr)) // read again! this byte will
be lost soon :(
}
ct.toString()
Regards,
Laurent
Le dimanche 26 décembre 2021 à 18:12:56 UTC+1, hank....@gmail.com a écrit :
> Hi --
> Thanks for taking the time to help me.
> As far as I understand the examples, loop has this template:
>
> loop [binding]
> (condition
> (statement)
> (recur (binding)))
> And in 'recur' the loop is re-executed with new bindings.
>
> There was indeed an issue with the 'recur' outside 'when'. Thanks for
> pointing that out.
> I corrected that in the version below.
>
> I also changed to a smaller file (UTF-8 encoded in Linux), called
> 'ribs.txt', with the following content:
>
> source/txt on master [!?]
> ❯ cat ribs.txt
> Try my delicious pork-chop ribs!
>
> source/txt on master [!?]
> ❯ cat ribs.hexdump
> 00000000: 54 72 79 20 6d 79 20 64 65 6c 69 63 69 6f 75 73 Try my delicious
> 00000010: 20 70 6f 72 6b 2d 63 68 6f 70 20 72 69 62 73 21 pork-chop ribs!
> 00000020: 0a .
>
>
> (defn pt8 [file]
> (let [afr (FileReader. file); instances of FileReader, BufferedReader,
> StringBuffer
> bfr (BufferedReader. afr)
> ct (StringBuilder.)
> this-list (list afr bfr ct)]
> ; (apply println this-list)
> ; put recur INSIDE THE WHEN
> (loop [val (.read bfr)]
> (when (not (= val -1))
> (.append ct (Character/toChars (.read bfr)))
> (recur [val (.read bfr)])))
> ; when finished...
> (.toString ct)))
>
> I think this fixed the 'recur', because it does rebinding to a new call to
> "read()".
> However, the errors remains.
>
> user> (pt8 ribs)
> Execution error (IllegalArgumentException) at java.lang.Character/toChars
> (Character.java:8572).
> Not a valid Unicode code point: 0xFFFFFFFF
>
> The file used is sufficiently small so that we can walk the bytes using
> jshell:
>
> jshell> FileReader afr = new FileReader("/home/hank/source/txt/ribs.txt/")
> afr ==> java.io.FileReader@1698c449
>
> jshell> BufferedReader bfr = new BufferedReader(afr)
> bfr ==> java.io.BufferedReader@5ef04b5
>
> jshell> StringBuilder ct = new StringBuilder()
> ct ==>
>
> FileReader reads 2 bytes per character so, to get to the end, of the first
> hexdump line, let's walk 32 bytes:
>
> jshell> for (int i=0; i < 31; i++) {
> ...> if ((value = bfr.read()) != -1) { ct.append((char) value); }
> ...> i++;
> ...> }
>
> jshell> ct
> ct ==> Try my delicious
>
> 00000000: 54 72 79 20 6d 79 20 64 65 6c 69 63 69 6f 75 73 Try my delicious
> T r y SP m y SP d e l i c i o u s (<---- YOU ARE
> HERE)
>
> 00000000: 54 72 79 20 6d 79 20 64 65 6c 69 63 69 6f 75 73 Try my delicious
> 00000010: 20 70 6f 72 6b 2d 63 68 6f 70 20 72 69 62 73 21 pork-chop ribs!
> 00000020: 0a .
>
> Now we iterate 31 more bytes, stopping short of the last character:
> jshell> for (int i=0; i < 30; i++) {
> ...> if ((value = bfr.read()) != -1) { ct.append((char) value); }
> ...> i++;
> ...> }
>
> jshell> ct
> ct ==> Try my delicious pork-chop ribs
>
> 00000000: 54 72 79 20 6d 79 20 64 65 6c 69 63 69 6f 75 73 Try my delicious
> 00000010: 20 70 6f 72 6b 2d 63 68 6f 70 20 72 69 62 73 21 pork-chop ribs!
> ^ we stopped here
>
> We just advance one more:
>
> jshell> if ((value = bfr.read()) != -1) { ct.append((char) value); }
> ...>
>
> jshell> ct
> ct ==> Try my delicious pork-chop ribs!
>
> And one more time, to see if it borks:
> jshell> if ((value = bfr.read()) != -1) { ct.append((char) value); }
>
> jshell> ct
> ct ==> Try my delicious pork-chop ribs!
>
> Nope, everything looks fine. Now where does that '0xFFFFFFF" come from?!
> -- Hank
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