[Haskell-cafe] [ANN] Haskell Cheatsheet v1.0

Thomas Hartman tphyahoo at gmail.com
Sat Oct 11 07:33:16 EDT 2008

Very nice!

I have my own cheat list, which are haskell commands I find useful but
find inconvenient or difficult to look up in the supplied
documentation. I actually hardwire my cheats into .bashrc doing
something like

thartman_haskell_cheatting() {

cat << EOF
  blah blah


so i can quickly see all my haskell cheats using tab completion. but a
pdf is even nicer :)


thartman at thartman-laptop:~/Desktop>thartman_haskell_oneliners
  ghc -e '1+2'

thartman at thartman-laptop:~/Desktop>thartman_haskell_regex_hints
  cabal install pcre-regex

  Most likely want:

  Prelude Text.Regex.PCRE> "user123" =~ "^(user)(\d*)$" ::
  That is: (before match, match, after match, subgroups)

  or maybe
    Prelude Text.Regex.PCRE>  "user123 user456" =~ "(u(se)r)(\d*)" :: [[String]]
    if you need all submatches of all matches

      Prelude Text.Regex.PCRE> "user123 user456" =~ "(user)(\d*)" ::
      ("","user123"," user456",["user","123"])
      doesn't quite do what I want -- no submatches
      and there's no instance for :: (String,String,String,[String])
    I don't need all submatches of all matches very often though.

  :: Bool -- did it match
  :: String -- first match
  :: [String] -- every match
  :: :: (String,String,String) -- before, matched, after


thartman at thartman-laptop:~/Desktop>thartman_haskell_testing_things
  import Data.Test.HUnit
  runTestTT $ TestCase $ assertEqual "meh" 1 2
  runTestTT $ TestList [ TestCase $ assertEqual "meh" 1 2 ]

thartman at thartman-laptop:~/Desktop>thartman_haskell_hints
  offline documentation:
    ghc-pkg describe bytestring | grep -i doc
      or probably just
      haddock-html: /usr/local/share/doc/ghc/libraries/bytestring
    note to self:
      start using cabal install --global (or whatever the flag is)
        so all documentation is browsable from one place

  Use language pragmas, with commas
  And you can't put LANGUAGE and OPTIONS_GHC in the same pragma
    {-# LANGUAGE NoMonomorphismRestriction, PatternSignatures #-}
    {-# OPTIONS -fglasgow-exts #-}


      Couldn't match expected type 'blee'
             against inferred type 'bleh'
    bleh is whatever is at 30:17
    blee is something that's wanted by whatever is calling the value at 30:17

    If the error is "in the definition of" some function,
    then probably one function case conflicts with another, you can
ignore other functions.
    In this case you will only get one line:col to look at.
    If there are more than one line:col to look at, possibly separate
functions are in conflict.
    So, smart to always fix "in the definition of" type errors first.

    Still baffled? Won't compile?
    Give top-level functions type signatures. Won't hurt, might help.
      :set -fwarn-missing-signatures
      or {-# OPTIONS -fwarn-missing-signatures #-}
    Start commenting out calling functions until it compiles, and then
look at the signatures.
    And then type the signatures in explicitly... does something look funny?
      Like, wrong number of args? Maybe currying went wrong.

  tag and bundle a distribution:
    darcs tag 0.2
    cabal configure
    cabal sdist
    cd dist; unzip, verify install does the right thing
    check upload, and upload.
    see also http://en.wikibooks.org/wiki/Haskell/Packaging

  group module imports from multiple modules in one place:
    module MyInductiveGraph (
      module Data.Graph.Inductive,
      module EnoughFlow
    import Data.Graph.Inductive
    import EnoughFlow

2008/10/11 Justin Bailey <jgbailey at gmail.com>:
> All,
> I've created a "cheat sheet" for Haskell. It's a PDF that tries to
> summarize Haskell 98's syntax, keywords and other language elements.
> It's currently available on hackage[1]. Once downloaded, unpack the
> archive and you'll see the PDF. A literate source file is also
> included.
> If you install with "cabal install cheatsheet", run "cheatsheet"
> afterwards and the program will tell you where the PDF is located.
> The audience for this document is beginning to intermediate Haskell
> programmers. I found it difficult to look up some of the less-used
> syntax and other language stumbling blocks as I learned Haskell over
> the last few years, so I hope this document can help others in the
> future.
> This is a beta release (which is why I've limited the audience by
> using hackage) to get feedback before distributing the PDF to a wider
> audience. With that in mind, I welcome your comments or patches[2].
> Justin
> [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/CheatSheet
> [2] git://github.com/m4dc4p/cheatsheet.git
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe

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