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Haskell version of Norvig's spelling corrector

marcosero.com

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Re: Haskell version of Norvig's spelling corrector

#11

Post by wyager »

marcosero wrote: post #9
quchen wrote: post #4

> I wrote this code putting brevity over readability, which is something I usually never do Shouldn't the point of such a post be to show interesting code? I'm having trouble reading through the densely packed source. In addition to tromp's minor nitpick, I have several major ones. - the code is full of redundant parentheses. HLint can detect those (and many other style errors) automatically. LPaste has HLint install…

Hi, author here. I think you partially missed the main purpose of the article, which for me was just having fun by playing with a language I'm currently learning. I wasn't try to teach anything to anyone. But I must say, thanks for the great feedback! Lots of stuff I didn't know that we'll make me write better Haskell code :)

I expect there to be lots of comments demonstrating tons of different styles of doing this stuff. Haskell is one of those languages where you can go back to your code 20 times and still find a new way of doing something.

Re: Haskell version of Norvig's spelling corrector

#12

Post by flebron »

marcosero wrote: post #9
quchen wrote: post #4

> I wrote this code putting brevity over readability, which is something I usually never do Shouldn't the point of such a post be to show interesting code? I'm having trouble reading through the densely packed source. In addition to tromp's minor nitpick, I have several major ones. - the code is full of redundant parentheses. HLint can detect those (and many other style errors) automatically. LPaste has HLint install…

Hi, author here. I think you partially missed the main purpose of the article, which for me was just having fun by playing with a language I'm currently learning. I wasn't try to teach anything to anyone. But I must say, thanks for the great feedback! Lots of stuff I didn't know that we'll make me write better Haskell code :)

Well, what you wrote is "The main reason I did it was to see what Haskell is capable of compared to other languages such as Python." The problem is that what you coded isn't what Haskell is capable of :)

Re: Haskell version of Norvig's spelling corrector

#14

Post by chaoxu »

marcosero wrote: post #9
quchen wrote: post #4

> I wrote this code putting brevity over readability, which is something I usually never do Shouldn't the point of such a post be to show interesting code? I'm having trouble reading through the densely packed source. In addition to tromp's minor nitpick, I have several major ones. - the code is full of redundant parentheses. HLint can detect those (and many other style errors) automatically. LPaste has HLint install…

Hi, author here. I think you partially missed the main purpose of the article, which for me was just having fun by playing with a language I'm currently learning. I wasn't try to teach anything to anyone. But I must say, thanks for the great feedback! Lots of stuff I didn't know that we'll make me write better Haskell code :)

It would be nice if you explicitly state you are learning Haskell in your article. If I'm a newbie and I see some of the awkward Haskell code(which I also make sometimes), I would feel discouraged. It doesn't seem Haskell is making things better.

Re: Haskell version of Norvig's spelling corrector

#15

Post by codygman »

wyager wrote: post #10

Cool! Since we're suggesting changes, here's what I'd do. (Not that anything is wrong with the OP's code, just that it's good to point out all the different stylistic techniques you can adopt.) 7. alphabet = ['a'..'z'] 8. nWords = B.readFile "big.txt" >>= return . train . lowerWords . B.unpack or: 8. nWords = train . lowerWords . B.unpack B.readFile "big.txt" Make `splits`, `deletes`, etc. values (not functions). `sp…

I used to compose return with a series of pure functions as well, but I found that using liftM seems cleaner.

Re: Haskell version of Norvig's spelling corrector

#16

Post by dschiptsov »

dschiptsov wrote: post #7

Which "proves" again that programming is neither about OO nor about purity..)

Where I am wrong? This is a straight-forward translation of non-OO Python code into Haskell, isn't it?

So there we can't see any "benefits" of truly-OO (original code has been written in a "functional style") or pure-functional approaches (the code has no "benefits" being converted into a pure-functional language).

Lists and Sets are "classes" in Python, but it doesn't matter, because implementation of "basic" types does not alter the behavior - sets could be implemented out of Lisp's conses.

Btw, knowing who the author is and seeing some "functional patterns" in Python code, it is very probable that original corrector has been prototyped/written in Common Lisp, then re-written in Python, and now re-written in Haskell.

The point was in an elegant algorithm and compact implementation, not in language of choice or in particular programming paradigm.

Re: Haskell version of Norvig's spelling corrector

#17

Post by evincarofautumn »

quchen wrote: post #6
evincarofautumn wrote: post #5

Earlier quoted context omitted.

As long as we’re picking nits… > I wrote this code putting brevity over readability Overall, this is not particularly terse, for Haskell code. With all the lambdas, it looks like OCaml! For example, these are equivalent, and I find the latter clearer: (sortBy (\(_,c1)(_,c2) -> c2 `compare` c1)) sortBy (flip (comparing snd)) Now, it’s not necessarily a bad thing to be explicit, but in cases such as these, it’s less re…

For reverse sorting, there's a type that does specifically that. sortBy (comparing (Down . snd)) See http://hackage.haskell.org/package/base-4.7.0.1/docs/Data-Or...

True, but I prefer not to use typeclasses in that way.

Re: Haskell version of Norvig's spelling corrector

#18

Post by codygman »

codygman wrote: post #15
wyager wrote: post #10

Cool! Since we're suggesting changes, here's what I'd do. (Not that anything is wrong with the OP's code, just that it's good to point out all the different stylistic techniques you can adopt.) 7. alphabet = ['a'..'z'] 8. nWords = B.readFile "big.txt" >>= return . train . lowerWords . B.unpack or: 8. nWords = train . lowerWords . B.unpack B.readFile "big.txt" Make `splits`, `deletes`, etc. values (not functions). `sp…

I used to compose return with a series of pure functions as well, but I found that using liftM seems cleaner.

example:

    nWords = liftM (train . lowerWords . B.unpack) (B.readFile "big.txt")
There was recently a very good article[0] about practically using monads that mentioned using liftM.

However whenever using a functor instance is possible it's probably better, since functors can't do as much as monads. I'm not quite sure how much this would help/apply to this small example though.

0: http://softwaresimply.blogspot.com/2014/12/ltmt-part-3-monad...

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