Re: [Haskell-cafe] Code critique - Was [Maybe Int] sans Nothings
Nice tool. I'll be using it a lot from now on, I'm sure. Thanks, Neil.
Michael
--- On Mon, 5/30/11, Neil Mitchell wrote:
From: Neil Mitchell
Subject: Re: [Haskell-cafe] Code critique - Was [Maybe Int] sans Nothings
To: "michael rice"
Cc: "Haskell Cafe" , "Alexander Solla"
Date: Monday, May 30, 2011, 1:55 PM
Hi Michael,
You've used quite a few entirely redundant brackets. The tool HLint
(http://community.haskell.org/~ndm/hlint) will tell you which ones.
Thanks, Neil
On Wed, May 25, 2011 at 12:09 AM, michael rice wrote:
The input file: http://dl.dropbox.com/u/27842656/psalms
The Markov chain exercise from "The Practice of Programming", Kermighan/Pike.
Sample runs at the end.
Michael
import System.Environment(getArgs)import System.Randomimport
Control.Applicativeimport Control.Monad.Reader
import Control.Monad.Stateimport Data.Maybeimport Data.Map
type Prefix = (String,String)type GeneratorState1 = State ((Map Prefix
[String]),Prefix,[String])
type GeneratorState2 = StateT (Prefix,StdGen) (Reader (Map Prefix [String]))
non_word = "\n"
f key new old = new ++ old
buildMap :: GeneratorState1 (Map Prefix [String])
buildMap = do (mp,(pfx1,pfx2),words) <- get if (Prelude.null
words) then {-
No more words. Return final map (adding non_word for final prefix). -}
return (insertWithKey' f (pfx1,pfx2) [non_word] mp)
else do {- Add word to map at prefix & continue. -}
put (insertWithKey' f (pfx1,pfx2) [head words] mp,
(pfx2,(head words)), tail words) buildMap
generate :: GeneratorState2 (Maybe String)
generate = do ((pfx1,pfx2),gen) <- get mp <- ask let
suffixList = mp ! (pfx1,pfx2) let (index,newGen) = randomR (0,
(length suffixList)-1)
gen let word = suffixList !! index if (word ==
non_word) then return Nothing
else do
put ((pfx2,word),newGen) return (Just word)
rInt :: String -> IntrInt = read
main = do (seed:nwords:_) <- (Prelude.map rInt) <$> getArgs
contents <- getContents putStrLn $ unwords $ catMaybes $
runReader (evalStateT (sequence $
replicate nwords generate) ((non_word,non_word),mkStdGen seed))
(evalState buildMap (singleton
(non_word,non_word) [], (non_word,non_word), words contents))
{-[michael@hostname ~]$ ghc --make markov.hs[1 of 1] Compiling Main
( markov.hs, markov.o )Linking markov ...[michael@hostname ~]$ cat psalms |
./markov 111 100
Blessed is the LORD, in thine own cause: remember how the foolish people have
blasphemed thy name. In the courts of the righteous: The LORD taketh pleasure
in the desert. And he led them with the wicked, and with the whole earth, is
mount Zion, on the sides of thine only. O God, and was troubled: I complained,
and my God. My
times are in thy praise. Blessed be God, which is full of the LORD is good:
for his wondrous works. Now also when I am small and despised: yet do I put my
trust: how say ye to[michael@hostname ~]$ cat psalms | ./markov 666 100
Blessed is the LORD, and cried unto thee, Thy face, LORD, will I remember thee
from the beginning: and every one that is weaned of his heart to any wicked
transgressors. Selah. They return at evening: they make ready their arrow upon
the people; and thou hast destroyed all them that fight against them that trust
in thee: and let my tongue cleave to the heavens by his power for ever; and thy
lovingkindnesses; for they have laid a snare before them: and that my ways were
directed to keep thy word. Mine eyes fail while I have said that
[michael@hostname ~]$
--- On Tue,
5/24/11, Alexander Solla wrote:
From: Alexander Solla
Subject: Re: [Haskell-cafe] [Maybe Int] sans Nothings
To: "Haskell Cafe"
Date: Tuesday, May 24, 2011, 5:01 PM
> Personally, I find non-functional values without Eq instances to be
> degenerate. So I really do not mind superfluous Eq constraints. I
> would not hesitate to use filter ((/=) Nothing) in a function whose type
> has no free type variables. It's just a bit of plumbing inside of a
> more complex function.
Sometimes it seems to be better to not allow Eq on Float and Double.
Since most algebraic laws do not hold for those types, it is more often
an error than an intention to compare two Float values. And how to
compare (IO a) values?
Floats, Doubles, and IO are all "degenerate" types, for the reasons you
outline. (Admittedly, Float and Double have Eq instances, but invalid Eq
semantics) Notice how their value semantics each depend on the machine your
runtime runs on, as opposed to merely the runtime. Bottom is another one of
thes
Re: [Haskell-cafe] Code critique - Was [Maybe Int] sans Nothings
Hi Michael,
You've used quite a few entirely redundant brackets. The tool HLint (
http://community.haskell.org/~ndm/hlint) will tell you which ones.
Thanks, Neil
On Wed, May 25, 2011 at 12:09 AM, michael rice wrote:
> The input file: http://dl.dropbox.com/u/27842656/psalms
>
> The Markov chain exercise from "The Practice of Programming",
> Kermighan/Pike. Sample runs at the end.
>
> Michael
>
>
>
> import System.Environment(getArgs)
> import System.Random
> import Control.Applicative
> import Control.Monad.Reader
> import Control.Monad.State
> import Data.Maybe
> import Data.Map
>
> type Prefix = (String,String)
> type GeneratorState1 = State ((Map Prefix [String]),Prefix,[String])
> type GeneratorState2 = StateT (Prefix,StdGen) (Reader (Map Prefix
> [String]))
>
> non_word = "\n"
>
> f key new old = new ++ old
>
> buildMap :: GeneratorState1 (Map Prefix [String])
> buildMap = do (mp,(pfx1,pfx2),words) <- get
> if (Prelude.null words)
> then {- No more words. Return final map (adding non_word
> for final prefix). -}
> return (insertWithKey' f (pfx1,pfx2) [non_word] mp)
> else do {- Add word to map at prefix & continue. -}
> put (insertWithKey' f (pfx1,pfx2) [head words] mp,
> (pfx2,(head words)), tail words)
> buildMap
>
> generate :: GeneratorState2 (Maybe String)
> generate = do ((pfx1,pfx2),gen) <- get
> mp <- ask
> let suffixList = mp ! (pfx1,pfx2)
> let (index,newGen) = randomR (0, (length suffixList)-1) gen
> let word = suffixList !! index
> if (word == non_word)
> then
> return Nothing
> else do
> put ((pfx2,word),newGen)
> return (Just word)
>
> rInt :: String -> Int
> rInt = read
>
> main = do (seed:nwords:_) <- (Prelude.map rInt) <$> getArgs
> contents <- getContents
> putStrLn $ unwords $ catMaybes $ runReader (evalStateT (sequence
> $ replicate nwords generate) ((non_word,non_word),mkStdGen seed))
> (evalState buildMap
> (singleton (non_word,non_word) [], (non_word,non_word), words contents))
>
> {-
> [michael@hostname ~]$ ghc --make markov.hs
> [1 of 1] Compiling Main ( markov.hs, markov.o )
> Linking markov ...
> [michael@hostname ~]$ cat psalms | ./markov 111 100
> Blessed is the LORD, in thine own cause: remember how the foolish people
> have blasphemed thy name. In the courts of the righteous: The LORD taketh
> pleasure in the desert. And he led them with the wicked, and with the whole
> earth, is mount Zion, on the sides of thine only. O God, and was troubled: I
> complained, and my God. My times are in thy praise. Blessed be God, which is
> full of the LORD is good: for his wondrous works. Now also when I am small
> and despised: yet do I put my trust: how say ye to
> [michael@hostname ~]$ cat psalms | ./markov 666 100
> Blessed is the LORD, and cried unto thee, Thy face, LORD, will I remember
> thee from the beginning: and every one that is weaned of his heart to any
> wicked transgressors. Selah. They return at evening: they make ready their
> arrow upon the people; and thou hast destroyed all them that fight against
> them that trust in thee: and let my tongue cleave to the heavens by his
> power for ever; and thy lovingkindnesses; for they have laid a snare before
> them: and that my ways were directed to keep thy word. Mine eyes fail while
> I have said that
> [michael@hostname ~]$
>
> --- On *Tue, 5/24/11, Alexander Solla * wrote:
>
>
> From: Alexander Solla
> Subject: Re: [Haskell-cafe] [Maybe Int] sans Nothings
> To: "Haskell Cafe"
> Date: Tuesday, May 24, 2011, 5:01 PM
>
>
> > Personally, I find non-functional values without Eq instances to be
> > degenerate. So I really do not mind superfluous Eq constraints. I
> > would not hesitate to use filter ((/=) Nothing) in a function whose type
> > has no free type variables. It's just a bit of plumbing inside of a
> > more complex function.
>
> Sometimes it seems to be better to not allow Eq on Float and Double.
> Since most algebraic laws do not hold for those types, it is more often
> an error than an intention to compare two Float values. And how to
> compare (IO a) values?
>
>
> Floats, Doubles, and IO are all "degenerate" types, for the reasons you
> outline. (Admittedly, Float and Double have Eq instances, but invalid Eq
> semantics) Notice how their value semantics each depend on the machine your
> runtime runs on, as opposed to merely the runtime. Bottom is another one of
> these degenerate types, since comparisons on arbitrary values are
> undecidable.
>
> Also, by thinking about function types, you often
> get interesting use cases. Thus I would not assume too quickly that a
> type will always be instantiated by types other than a function type.
> T
Re: [Haskell-cafe] Code critique - Was [Maybe Int] sans Nothings
Yes, very nice. Thanks.
Michael
--- On Wed, 5/25/11, Henning Thielemann
wrote:
From: Henning Thielemann
Subject: Re: [Haskell-cafe] Code critique - Was [Maybe Int] sans Nothings
To: "michael rice"
Cc: "Haskell Cafe"
Date: Wednesday, May 25, 2011, 3:41 AM
Alexander Solla schrieb:
> buildMap :: GeneratorState1 (Map Prefix [String])
> buildMap = do (mp,(pfx1,pfx2),words) <- get
> if (Prelude.null words)
> then {- No more words. Return final map (adding
> non_word for final prefix). -}
> return (insertWithKey' f (pfx1,pfx2) [non_word] mp)
> else do {- Add word to map at prefix & continue. -}
> put (insertWithKey' f (pfx1,pfx2) [head words] mp,
> (pfx2,(head words)), tail words)
> buildMap
>
>>>> I'm not a fan of explicit if-then-else's, but my preferred
case words of
[] -> {- no more words -} ...
w:ws -> ...
would work perfectly.
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Re: [Haskell-cafe] Code critique - Was [Maybe Int] sans Nothings
Alexander Solla schrieb:
> buildMap :: GeneratorState1 (Map Prefix [String])
> buildMap = do (mp,(pfx1,pfx2),words) <- get
> if (Prelude.null words)
> then {- No more words. Return final map (adding
> non_word for final prefix). -}
> return (insertWithKey' f (pfx1,pfx2) [non_word] mp)
> else do {- Add word to map at prefix & continue. -}
> put (insertWithKey' f (pfx1,pfx2) [head words] mp,
> (pfx2,(head words)), tail words)
> buildMap
>
I'm not a fan of explicit if-then-else's, but my preferred
case words of
[] -> {- no more words -} ...
w:ws -> ...
would work perfectly.
___
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Haskell-Cafe@haskell.org
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Re: [Haskell-cafe] Code critique - Was [Maybe Int] sans Nothings
Thanks, Alexander. Not as much red ink as I was expecting.
My monitor is acting up, so I may be be dropping off the radar unexpectedly
while acquiring a replacement.
Each prefix is guaranteed to have at least one following word in its suffix
list (possibly more) because the map is built from the actual Psalms text. The
only prefix for which this does not occur is the final two words of the text,
thus the TRUE case in buildMap puts the sole non_word in the suffix list.
The generate function then _always_ builds a prefix from the first two words of
the text, "Blessed is," looks up its suffix list, chooses the next word
randomly, and creates a new prefix by pairing the second word of the old prefix
and the new word. Repeat.
I've attached the AWK and C++ sources for the same Markov exercise if you wish
to examine them. Both just write a single word on each line so I cobbled a
Haskell program (lines.hs) to turn them into lines.
Michael
--- On Tue, 5/24/11, Alexander Solla wrote:
From: Alexander Solla
Subject: Re: [Haskell-cafe] Code critique - Was [Maybe Int] sans Nothings
To: "michael rice"
Cc: "Haskell Cafe"
Date: Tuesday, May 24, 2011, 10:42 PM
My comments are in-line, marked off with >>>
On Tue, May 24, 2011 at 4:09 PM, michael rice wrote:
The input file: http://dl.dropbox.com/u/27842656/psalms
The Markov chain exercise from "The Practice of Programming", Kermighan/Pike.
Sample runs at the end.
Michael
import System.Environment(getArgs)import System.Randomimport
Control.Applicativeimport Control.Monad.Reader
import Control.Monad.Stateimport Data.Maybeimport Data.Map
type Prefix = (String,String)type GeneratorState1 = State ((Map Prefix
[String]),Prefix,[String])
type GeneratorState2 = StateT (Prefix,StdGen) (Reader (Map Prefix [String]))
non_word = "\n"
f key new old = new ++ old
>>> I don't see what f is for, since it doesn't do anything with the key.
buildMap :: GeneratorState1 (Map Prefix [String])buildMap = do
(mp,(pfx1,pfx2),words) <- get
if (Prelude.null words) then {-
No more words. Return final map (adding non_word for final prefix). -}
return (insertWithKey' f (pfx1,pfx2) [non_word] mp)
else do {- Add word to map at prefix & continue. -}
put (insertWithKey' f (pfx1,pfx2) [head words] mp,
(pfx2,(head words)), tail words) buildMap
>>> I'm not a fan of explicit if-then-else's, but my preferred alternative
>>> won't win much either.
>>> (see http://osdir.com/ml/haskell-cafe@haskell.org/2011-05/msg00612.html for
>>> an example of what I'm talking about)
generate :: GeneratorState2 (Maybe String)generate = do ((pfx1,pfx2),gen) <-
get mp <- ask let suffixList = mp ! (pfx1,pfx2)
>>> I'm not sure how you're guaranteed that mp ! (pfx1, pfx2) exists, at first
>>> glance. "lookup" uses Maybe semantics, in the case there is no result.
let (index,newGen) = randomR (0, (length suffixList)-1)
gen
>>> I might use a function like:>>> listRange :: [a] -> (Int, Int)>>> listRange
>>> list = (0, (length $ l) - 1)
>>> This is a common enough pattern to abstract away.
let word = suffixList !! index if (word ==
non_word) then return Nothing
else do put ((pfx2,word),newGen)
return (Just word)
rInt :: String -> IntrInt = read
>>> rInt is fair enough, but you can also have the same effect with an
explicit type signature ((read n) :: Int) I tend to prefer the latter,
personally.
main = do (seed:nwords:_) <- (Prelude.map rInt) <$> getArgs contents
<- getContents putStrLn $ unwords $ catMaybes $ runReader (evalStateT
(sequence $
replicate nwords generate) ((non_word,non_word),mkStdGen seed))
(evalState buildMap (singleton
(non_word,non_word) [], (non_word,non_word), words contents))
>>> Nice use of functor application.
{-[michael@hostname ~]$ ghc --make markov.hs[1 of 1] Compiling Main
( markov.hs, markov.o )
Linking markov ...[michael@hostname ~]$ cat psalms | ./markov 111 100Blessed is
the LORD, in thine own cause: remember how the foolish people have blasphemed
thy name. In the courts of the righteous: The LORD taketh pleasure in the
desert. And he led them with the wicked, and with the whole earth, is mount
Zion, on the sides of thine only. O God, and was troubled: I complained, and my
God. My
times are in thy praise. Blessed be God, which is full of the LORD is good:
for his wondrous works. Now also when I am small
Re: [Haskell-cafe] Code critique - Was [Maybe Int] sans Nothings
My comments are in-line, marked off with >>>
On Tue, May 24, 2011 at 4:09 PM, michael rice wrote:
> The input file: http://dl.dropbox.com/u/27842656/psalms
>
> The Markov chain exercise from "The Practice of Programming",
> Kermighan/Pike. Sample runs at the end.
>
> Michael
>
>
>
> import System.Environment(getArgs)
> import System.Random
> import Control.Applicative
> import Control.Monad.Reader
> import Control.Monad.State
> import Data.Maybe
> import Data.Map
>
> type Prefix = (String,String)
> type GeneratorState1 = State ((Map Prefix [String]),Prefix,[String])
> type GeneratorState2 = StateT (Prefix,StdGen) (Reader (Map Prefix
> [String]))
>
> non_word = "\n"
>
> f key new old = new ++ old
>
>
>>> I don't see what f is for, since it doesn't do anything with the key.
> buildMap :: GeneratorState1 (Map Prefix [String])
> buildMap = do (mp,(pfx1,pfx2),words) <- get
> if (Prelude.null words)
> then {- No more words. Return final map (adding non_word
> for final prefix). -}
> return (insertWithKey' f (pfx1,pfx2) [non_word] mp)
> else do {- Add word to map at prefix & continue. -}
> put (insertWithKey' f (pfx1,pfx2) [head words] mp,
> (pfx2,(head words)), tail words)
> buildMap
>
> >>> I'm not a fan of explicit if-then-else's, but my preferred alternative
won't win much either. (see
http://osdir.com/ml/haskell-cafe@haskell.org/2011-05/msg00612.html for an
example of what I'm talking about)
> generate :: GeneratorState2 (Maybe String)
> generate = do ((pfx1,pfx2),gen) <- get
> mp <- ask
> let suffixList = mp ! (pfx1,pfx2)
>
>>> I'm not sure how you're guaranteed that mp ! (pfx1, pfx2) exists, at
first glance. "lookup" uses Maybe semantics, in the case there is no
result.
> let (index,newGen) = randomR (0, (length suffixList)-1) gen
>
>>> I might use a function like:
>>> listRange :: [a] -> (Int, Int)
>>> listRange list = (0, (length $ l) - 1)
>>> This is a common enough pattern to abstract away.
let word = suffixList !! index
> if (word == non_word)
> then
> return Nothing
> else do
> put ((pfx2,word),newGen)
> return (Just word)
>
> rInt :: String -> Int
> rInt = read
>
>
>>> rInt is fair enough, but you can also have the same effect with an
explicit type signature ((read n) :: Int) I tend to prefer the latter,
personally.
> main = do (seed:nwords:_) <- (Prelude.map rInt) <$> getArgs
> contents <- getContents
> putStrLn $ unwords $ catMaybes $ runReader (evalStateT (sequence
> $ replicate nwords generate) ((non_word,non_word),mkStdGen seed))
> (evalState buildMap
> (singleton (non_word,non_word) [], (non_word,non_word), words contents))
>
> >>> Nice use of functor application.
> {-
> [michael@hostname ~]$ ghc --make markov.hs
> [1 of 1] Compiling Main ( markov.hs, markov.o )
> Linking markov ...
> [michael@hostname ~]$ cat psalms | ./markov 111 100
> Blessed is the LORD, in thine own cause: remember how the foolish people
> have blasphemed thy name. In the courts of the righteous: The LORD taketh
> pleasure in the desert. And he led them with the wicked, and with the whole
> earth, is mount Zion, on the sides of thine only. O God, and was troubled: I
> complained, and my God. My times are in thy praise. Blessed be God, which is
> full of the LORD is good: for his wondrous works. Now also when I am small
> and despised: yet do I put my trust: how say ye to
> [michael@hostname ~]$ cat psalms | ./markov 666 100
> Blessed is the LORD, and cried unto thee, Thy face, LORD, will I remember
> thee from the beginning: and every one that is weaned of his heart to any
> wicked transgressors. Selah. They return at evening: they make ready their
> arrow upon the people; and thou hast destroyed all them that fight against
> them that trust in thee: and let my tongue cleave to the heavens by his
> power for ever; and thy lovingkindnesses; for they have laid a snare before
> them: and that my ways were directed to keep thy word. Mine eyes fail while
> I have said that
> [michael@hostname ~]$
>
> --- On *Tue, 5/24/11, Alexander Solla * wrote:
>
>
> From: Alexander Solla
> Subject: Re: [Haskell-cafe] [Maybe Int] sans Nothings
> To: "Haskell Cafe"
> Date: Tuesday, May 24, 2011, 5:01 PM
>
>
> > Personally, I find non-functional values without Eq instances to be
> > degenerate. So I really do not mind superfluous Eq constraints. I
> > would not hesitate to use filter ((/=) Nothing) in a function whose type
> > has no free type variables. It's just a bit of plumbing inside of a
> > more complex function.
>
> Sometimes it seems to be better to not allow Eq on Float and Double.
> Since most algebraic laws do not hold for those types, it is
Re: [Haskell-cafe] Code critique - Was [Maybe Int] sans Nothings
The input file: http://dl.dropbox.com/u/27842656/psalms
The Markov chain exercise from "The Practice of Programming", Kermighan/Pike.
Sample runs at the end.
Michael
import System.Environment(getArgs)import System.Randomimport
Control.Applicativeimport Control.Monad.Readerimport Control.Monad.Stateimport
Data.Maybeimport Data.Map
type Prefix = (String,String)type GeneratorState1 = State ((Map Prefix
[String]),Prefix,[String])type GeneratorState2 = StateT (Prefix,StdGen) (Reader
(Map Prefix [String]))
non_word = "\n"
f key new old = new ++ old
buildMap :: GeneratorState1 (Map Prefix [String])buildMap = do
(mp,(pfx1,pfx2),words) <- get if (Prelude.null words)
then {- No more words. Return final map (adding non_word for final prefix).
-} return (insertWithKey' f (pfx1,pfx2) [non_word] mp)
else do {- Add word to map at prefix & continue. -} put
(insertWithKey' f (pfx1,pfx2) [head words] mp, (pfx2,(head words)), tail
words) buildMap
generate :: GeneratorState2 (Maybe String)generate = do ((pfx1,pfx2),gen) <-
get mp <- ask let suffixList = mp ! (pfx1,pfx2)
let (index,newGen) = randomR (0, (length suffixList)-1) gen
let word = suffixList !! index if (word == non_word)
then return Nothing else do
put ((pfx2,word),newGen) return (Just word)
rInt :: String -> IntrInt = read
main = do (seed:nwords:_) <- (Prelude.map rInt) <$> getArgs contents
<- getContents putStrLn $ unwords $ catMaybes $ runReader (evalStateT
(sequence $ replicate nwords generate) ((non_word,non_word),mkStdGen seed))
(evalState buildMap (singleton
(non_word,non_word) [], (non_word,non_word), words contents))
{-[michael@hostname ~]$ ghc --make markov.hs[1 of 1] Compiling Main
( markov.hs, markov.o )Linking markov ...[michael@hostname ~]$ cat psalms |
./markov 111 100Blessed is the LORD, in thine own cause: remember how the
foolish people have blasphemed thy name. In the courts of the righteous: The
LORD taketh pleasure in the desert. And he led them with the wicked, and with
the whole earth, is mount Zion, on the sides of thine only. O God, and was
troubled: I complained, and my God. My times are in thy praise. Blessed be God,
which is full of the LORD is good: for his wondrous works. Now also when I am
small and despised: yet do I put my trust: how say ye to[michael@hostname ~]$
cat psalms | ./markov 666 100Blessed is the LORD, and cried unto thee, Thy
face, LORD, will I remember thee from the beginning: and every one that is
weaned of his heart to any wicked transgressors. Selah. They return at evening:
they make ready their arrow upon the
people; and thou hast destroyed all them that fight against them that trust in
thee: and let my tongue cleave to the heavens by his power for ever; and thy
lovingkindnesses; for they have laid a snare before them: and that my ways were
directed to keep thy word. Mine eyes fail while I have said
that[michael@hostname ~]$
--- On Tue, 5/24/11, Alexander Solla wrote:
From: Alexander Solla
Subject: Re: [Haskell-cafe] [Maybe Int] sans Nothings
To: "Haskell Cafe"
Date: Tuesday, May 24, 2011, 5:01 PM
> Personally, I find non-functional values without Eq instances to be
> degenerate. So I really do not mind superfluous Eq constraints. I
> would not hesitate to use filter ((/=) Nothing) in a function whose type
> has no free type variables. It's just a bit of plumbing inside of a
> more complex function.
Sometimes it seems to be better to not allow Eq on Float and Double.
Since most algebraic laws do not hold for those types, it is more often
an error than an intention to compare two Float values. And how to
compare (IO a) values?
Floats, Doubles, and IO are all "degenerate" types, for the reasons you
outline. (Admittedly, Float and Double have Eq instances, but invalid Eq
semantics) Notice how their value semantics each depend on the machine your
runtime runs on, as opposed to merely the runtime. Bottom is another one of
these degenerate types, since comparisons on arbitrary values are undecidable.
Also, by thinking about function types, you often
get interesting use cases. Thus I would not assume too quickly that a
type will always be instantiated by types other than a function type.
Thus I would stick to (filter isJust) and use this consistently for
monomorphic and polymorphic types.
I am not suggesting (filter ((/=) Nothing)) /over/ (filter isJust). Obviously,
once one is aware of a better tool, one should use it. But I am suggesting
that for simple cases which are unlikely to change in any substantive way, we
should probably just use the tools we already know of, as opposed to searching
for
