Attention Conservation Notice. Unqualified identifiers that are used the most on Hackage.

Perhaps you dread the error message:

Ambiguous occurrence `lookup' It could refer to either `Prelude.lookup', imported from Prelude or `Data.Map.lookup', imported from Data.Map

It is the message of the piper that has come to collect his dues for your unhygenic unqualified unrestricted module import style.

Or perhaps your a library writer and trying to think up of a new symbol for your funky infix combinator, but you aren't sure what other libraries have used already.

I took the archive (TAR) of the latest Hackage packages for everything, whipped up a script to extract all unqualified names exported by public modules, and then counted up the most used.

Disclaimer. Data constructors and record fields, unless they were explicitly exported, are not included in this count. I also don't count modules that export everything from the global namespace because they omitted a list of names to export. Counts are per module, and not per package. CPP and HSC files were not counted, due to limitations of haskell-src-exts.

Top twenty identifiers (as of September 2, 2012).

106 empty 69 insert 69 toList 66 fromList 56 null 54 singleton 44 run 42 encode 41 decode 41 delete 39 size 37 theModule 35 member 32 parse 31 get 30 lookup 30 union 29 Name 29 space 28 Node

Top twenty infix operators (as of September 2, 2012).

25 ! 19 <> 17 <+> 14 </> 11 <$> 10 // 10 >< 9 .: 9 <$$> 9 ∅ 8 & 8 .= 8 <?> 8 <||> 8 \\ 8 |> 7 # 7 $$ 7 *. 7 <->

The exclamation mark has earned the reputation as an "indexing" operator, and unsurprisingly is at the top. I hear from Edward Kmett that <> is making its way into the base as mappend , which is welcome, although might suck for the other six modules which redefined it for their own nefarious purposes.

All infix operators, sorted by usage and then lexicographically (as of September 2, 2012).

! <> <+> </> <$> // >< .: <$$> ∅ & .= <?> <||> \\ |> # $$ *. <-> <. <//> <| <|> ==> >. ||. ∈ ∉ !! &&. ++ +++ /=. <=. =: ==. >=. ∋ ∌ ∩ ∪ .|. :-> <: ? ∆ ∖ .&. .* .-. <&> <.> << === ?? @@ \/ ^^ |+ |- ||| ~~ !!! !> !? ## $+$ += +> -<- .*. .:? .<. .==. .>. /=? /\ :- :> :~> <$?> <+< <=> <=? <? <|?> =. ==? =~ >-> >=? >? @# ^ ~> ¬ ∘ ∧ ∨ ≡ ≢ ⊂ ⊃ ⊄ ⊅ ⊆ ⊇ ⊈ ⊉ !: $# $> $~ % %> && &&? &= ** *|* + --> ->- -| . .!= .!=. .&&. .&.? .*> .+ .++. .+. ... ./. ./\. .:: .<=. .=. .=> .>=. .\/. .| .||. :* :+ :. := :=: <*. <*> <++ <++> <..> <:> <<|> <== <|*|> =$= >+> >=> >>>= >|< ?> ?>= @@@ ^# ^$ ^: ^^^ |* || ||* ||+ ||? ~: ~? ≠ ≮ ≯ ⊕ ⧺ !$ !$? !. !=. !>>= #! #!! #~~ $ $! $$$ $$$? $$+ $$++ $$+- $$= $- $. $.// $/ $// $= $=! $? $| $~! %% %&& %+ %/= %: %< %<= %== %>= %|| &#& &&& &+ &. &.// &/ &// &=# &> &@ &| * *! *& *&&&* *&* ***** ****/* ****/*** ****//* ****//*** ****|* ****|*** ****||* ****||*** ***/* ***/** ***/**** ***//* ***//** ***//**** ***|* ***|** ***|**** ***||* ***||** ***||**** **. **/* **/*** **//* **//*** **> **|* **|*** **||* **||*** */* */** */*** */**** *//* *//** *//*** *//**** *<<<* *=* *=. *=>* *> *>>>* *? *@ *^ *|** *|*** *|**** *||* *||** *||*** *||**** +% ++. ++> ++>> ++@ +/+ +: +:+ +=. +>> +@ +^ +| - -!- -$ -->> -/\- -: -< -<< -<=- -=. -=> ->> -?- -?-> -?> -?>> -@ -\/- -^ -|- -~> .! .# .$. .- .--. .->. .... ./ ./= ./=. .:. .::: .< .<<. .<= .== .>>. .@ .@$ .@~ .\. .|| .~ .~. / /+/ /- /. /<-. /=: />/ /^ /| /~ /~? :*: :+: :-: :<-> :<: :<=: :<> :<~> :=+ :><: :~ <! <#$> <$| <% <&&> <* <+ <-$ <-- <-. <-: </=? <<! <</ <<: <<< <<? <<\ <<| <<~ <=! <=: <==? <=@ <=@@ <>>= <?< <??> <@ <@> <@@ <~ =$ =$$= =*= =/= =< =<< =<<! =<<< =<= =<>= =<? ==! =>> =~= =≪ >! >$$< >$< >*> >-- >-< >: >:> >=! >=: >== >===> >=>=> >=@ >=@@ >> >>-> >>. >>= >>=# >>== >>=\/ >>=|\/ >>=|| >>=||| >>> >>@ >?> >@ >@@ >||< ?! ?+ ?/= ?: ?< ?<= ?= ?== @! @= @==? @=? @? @?= @?== \== ^% ^-^ ^. ^>>= ^@ ^^. |#| |$> |*| |-> |-| |. |/ |// |: |<- |= |=> |=| |? |@ |\ |\\ |||| ~/= ~== ~=? ~?= ~|||~ ~||~ ~|~ ~~# ~~> ~~? ~~~> · ·× × ×· ÷ ⇒ ⇔ ∀ ∃ ≫ ≫= ⊛ ⊥ ⊨ ⊭ ⊲ ⊳ ⋅ ⋈ ⋘ ⋙ ▷ ◁ ★

It's a veritable zoo! (I'm personally reminded of Nethack.)

Source. The horrifying code that drove this exercise can be found at Github. I used the following shell one-liner:

for i in *; do for j in $i/*; do cd $j; tar xf *.tar.gz; cd ../..; done; done

to extract all of the tarballs inside the tar file.

Postscript. It would be neat if someone could fix the discrepancies that I described earlier and do a more comprehensive/correct search over this space.