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Today's Topics:
1. Re: Basic Trie Implementation: Request for Feedback and
QuickCheck Question (Dominik Bollmann)
2. regex and Unicode (Brian Sammon)
3. How do you show a Data.ByteArray? ([email protected])
4. Re: How do you show a Data.ByteArray? (David McBride)
5. Re: How do you show a Data.ByteArray? ([email protected])
----------------------------------------------------------------------
Message: 1
Date: Sun, 28 Aug 2016 14:26:40 +0200
From: Dominik Bollmann <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] Basic Trie Implementation: Request
for Feedback and QuickCheck Question
Message-ID:
<87k2f1w03j.fsf@t450s.i-did-not-set--mail-host-address--so-tickle-me>
Content-Type: text/plain
Just a short update, in case anyone reads along. I found the the problem
with question (2) from the previous mail: My Arbitrary instance for
TrieS was simply wrong and sometimes looped forever, which caused the
program to hang. Besides I found another bug (prefixes of words were
always found as well) which I've fixed now.
The updated code is here: http://lpaste.net/180994
Anyhow, if anyone has any suggestions on how to improve the code
style-wise, etc., I would be very happy to hear them!
Cheers, Dominik.
Dominik Bollmann <[email protected]> writes:
> Hello Haskellers,
>
> I just finished implementing a very simple Trie module, consisting of a
> Trie data type as well as operations `insert` and `lookup`. Function
> `insert` inserts a new element into the Trie; function lookup searches
> for all words in the Trie that match a specific pattern. Besides regular
> words, a pattern may consist of a single dot '.', indicating that at
> this position of the search term any letter may occur. For example a
> pattern "hello" would just search for the word "hello" in the Trie,
> while ".ello" would search words starting in *any* letter and followed
> by the sequence "ello" (i.e., it searches for "hello", "Hello", "Aello",
> etc.)
>
> The code for the Trie module can be found here: http://lpaste.net/180768.
>
> Regarding the code I have two questions:
>
> (1) Since I'm new to Haskell, I'd very much welcome feedback on the
> general implementation of the Trie module and its two methods what
> I could improve.
>
> (2) While testing the Trie module with QuickCheck, I wrote the
> property `prop_insert_then_lookup_succeeds` stating that after
> inserting a word into a Trie it can always successfully be looked
> up again. While quickchecking this property seems to succeed, I
> cannot verbose check it. In particular, when I run
>
> `verboseCheck prop_insert_then_lookup_succeeds`
>
> this property consumes all my main memory and results in the
> program hanging.
>
> Does anyone know what I messed up in devising the quickcheck
> property? I guess I left open some memory leak... Maybe it has to
> to with the Arbitrary instance which I might have defined
> incorrectly?
>
> Responses to any of the two questions above are very welcome :-)
>
> Thanks!
>
> Dominik.
------------------------------
Message: 2
Date: Sun, 28 Aug 2016 15:11:24 -0400
From: Brian Sammon <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] regex and Unicode
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=US-ASCII
I tried to write a program using Text.Regex.PCRE to search through a
UTF8-encoded document. It appears that the presence of non-breaking-space
characters (Charpoint 160) triggers some weird behavior in my program.
This is using the Debian stable(Jessie) packages of ghc 7.6.3 and libraries.
Now I find myself at a fork in the road, not sure which direction to head in.
Do I:
1) Continue looking (or get help with looking) for bugs in my code? (I
have this reduced to a pretty small test case)
2) Assemble a bug-report against debian?
3) Assemble a bug-report against Text.Regex.PCRE (or Text.Regex.Base) for
"upstream"
4) Uninstall Text.Regex.PCRE (and/or some other packages) and switch to
something that works with Unicode/UTF8?
Any ideas?
------------------------------
Message: 3
Date: Sun, 28 Aug 2016 22:56:29 +0000
From: [email protected]
To: [email protected]
Subject: [Haskell-beginners] How do you show a Data.ByteArray?
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Prelude Data.ByteArray> c = Data.ByteArray.zero 20
Prelude Data.ByteArray> :type c
c :: ByteArray ba => ba
Prelude Data.ByteArray> c
<interactive>:38:1: error:
• Ambiguous type variable ‘a0’ arising from a use of ‘print’
Uhm...
Prelude Data.ByteArray> index c 3
<interactive>:39:1: error:
• Ambiguous type variable ‘a0’ arising from a use of ‘index’
I can't print a byte?
------------------------------
Message: 4
Date: Sun, 28 Aug 2016 19:08:19 -0400
From: David McBride <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] How do you show a Data.ByteArray?
Message-ID:
<CAN+Tr4186Gy8rsJB4rsBzAMZyVrpC5RHY3QeifA=9xu122f...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
You haven't actually decided what c is, just that it is some type that is
an instance of the ByteArray class.
:i ByteArray
should show:
instance ByteArray ByteString
instance ByteArray Bytes
instance ByteArray ScrubbedBytes
try
print (c :: ByteString)
print (c :: ScrubbedBytes)
On Sun, Aug 28, 2016 at 6:56 PM, <[email protected]> wrote:
> Prelude Data.ByteArray> c = Data.ByteArray.zero 20
> Prelude Data.ByteArray> :type c
> c :: ByteArray ba => ba
> Prelude Data.ByteArray> c
>
> <interactive>:38:1: error:
> • Ambiguous type variable ‘a0’ arising from a use of ‘print’
>
> Uhm...
>
> Prelude Data.ByteArray> index c 3
>
> <interactive>:39:1: error:
> • Ambiguous type variable ‘a0’ arising from a use of ‘index’
>
> I can't print a byte?
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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------------------------------
Message: 5
Date: Mon, 29 Aug 2016 02:17:35 +0000
From: [email protected]
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] How do you show a Data.ByteArray?
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
On 08/28/2016 11:08 PM, David McBride wrote:
> You haven't actually decided what c is, just that it is some type that is an
> instance of the ByteArray class.
Thank you! I had thought there was a default instance, like it would by default
be Bytes, but could also optionally be wrapped around a ByteString or
ScrubbedBytes. But you're right, you can create "20 zeroes" of any of those
underlying things. Makes a lot more sense now.
------------------------------
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