Initially, I had written hackage-fetch to see if there was any use of coelgot anywhere on Hackage. At the time, there was not, but this has changed due to my gmpint package. As of writing, it is not surprisingly the only use of co-(Elgot algebra)s on the entirety of Hackage.

And Hackage is big! It's 12626 packages as of writing, totaling 37 million lines of code, 21.5 million of which are Haskell. You can see the table produced by polyglot below:

\-------------------------------------------------------------------------------
 Language             Files       Lines         Code     Comments       Blanks
-------------------------------------------------------------------------------
 Alex                   203       36652        29043         2387         5222
 Agda                    32        1578         1193           44          341
 Assembly                62       37757        35923         1334          500
 ATS                     36        4755         4057          311          387
 Autoconf               370      113138       107758         2133         3247
 Automake                16         906          635          116          155
 Bash                  1095       48554        29913        11462         7179
 Batch                   29         680          626            0           54
 Brainfuck                8         305          242            0           63
 C                     4554     3322442      2955363        28378       338701
 C--                      9        2011         1625           15          371
 C++                   1955     1993534      1798937        58140       136457
 C Header              5838     1986296      1845474            0       140822
 Cabal                14259      958586       861144        21730        75712
 Cabal Project          116         346          324            9           13
 Cassius                 47        1679         1390            0          289
 Coq                     11        5384         5102            0          282
 CSS                    647      136184       126341            0         9843
 Dhall                  511        5793         5597            0          196
 Elm                     60        6453         6344           25           84
 Emacs Lisp              71       26200        20530         2455         3215
 Erlang                   1          11            8            0            3
 FLTK Data               12        3150         3140            0           10
 Fortran                 51        5240         4697            0          543
 Go                      29         589          504            3           82
 Greencard                4         455          255           96          104
 Hamlet                 185        4704         4590            0          114
 Happy                  153       75841        58531         4810        12500
 Haskell             142502    22371322     16827551      2650653      2893118
 HTML                  1238      219099       205686            0        13413
 Idris                  634       37591        29174         1190         7227
 iPKG                    31         414          297            2          115
 Java                   354       50846        44730          466         5650
 JavaScript            2174     1254839      1125619         6148       123072
 Julius                  27        1149         1051            0           98
 Jupyter                  3         756          756            0            0
 Lex                    111         380          376            0            4
 LLVM                   100        7631         6266            0         1365
 Lua                     74       16892        13097         1115         2680
 M4                      60        5863         4884            0          979
 Madlang                 19         401          377            3           21
 Makefile               666       28330        20120         2246         5964
 Markdown              7515      434756       315136            0       119620
 Nix                    216       27154        22201            0         4953
 Objective C             31       11247         9524            0         1723
 OCaml                    1           9            7            0            2
 Perl                    30       12698        11749           65          884
 PHP                      6        1610         1474            0          136
 Plaintext             1895     4544911      4482274            0        62637
 Plutus                   3          25           25            0            0
 PowerShell               6         471          384            0           87
 Python                 110       28160        24012         2001         2147
 PureScript             672        9483         6937            0         2546
 R                       19        1235         1095            0          140
 Ruby                    15         463          396            0           67
 Rust                     1          12            3            5            4
 Scala                    2         100           78            0           22
 Swift                    7         630          592            0           38
 TCL                      5        1109          892            0          217
 TeX                   1528       49389        40684         2952         5753
 TOML                   167        1698         1255          129          314
 VHDL                     4         943          821            0          122
 Vimscript               84        5118         2616         2087          415
 Yacc                     1         435          381            0           54
 YAML                  5118      416583       377111         4864        34608
-------------------------------------------------------------------------------
 Total               195793    38322975     31488917      2807374      4026684
-------------------------------------------------------------------------------

So there's a lot of different stuff on Hackage. Some of that is unsurprising (Elm, PureScript, Dhall, Agda, and Idris are implemented in Haskell), but some of it is more off-beat (VHDL, Coq, ATS).

C is the second-most popular language, with 3.3 million lines of C on Hackage. This is somewhat surprising - it is one seventh as common as Haskell! Perhaps due to its prolixity, but nonetheless striking.

That's our brief tour of the ecosystem. Hopefully it manages to impress upon you the scale of extant Haskell, as well as some of the cross-pollination happening with other ecosystems.