align

Simple unix filter to align text on specified substrings.

align can be run from inside Vim or other editors with custom key bindings to align lines of code neatly on programming language operators like =>, ::, @=?, =, +, etc.

Installation

You must first have the Haskll platform installed on your system:

• Haskell platform

cabal update
cabal install align-text

This will likely install the align executable in ~/.cabal/bin, which should be on your PATH.

Usage

align has two modes: Serial mode and Alternative mode.

Serial mode

Assume you want to align this text:

input.sample:

    "parseKeyExpr" ~: [ObjectKey "item"] @=? parseKeyExpr "item"
  , "ngEvalToString" ~: "apple" @=? ngEvalToString testContext1 "item" 
  , "ngEvalToString2" ~: "apple" @=? ngEvalToString testContext2 "item.name" 

You can do so with this command:

align '~: @=?' < input.sample

which outputs:

    "parseKeyExpr"    ~: [ObjectKey "item"] @=? parseKeyExpr "item"
  , "ngEvalToString"  ~: "apple"            @=? ngEvalToString testContext1 "item"
  , "ngEvalToString2" ~: "apple"            @=? ngEvalToString testContext2 "item.name"

align takes an argument list of strings to align the text and performs the alignment operation on the text it gets from STDIN.

align will only match each alignment string once, so if that string occurs multiple times in a line, you need to specify it than many times in the argument.

Alternative mode

Assume you want to align this text:

input2.sample:

sendmailCustom :: FilePath        -- ^ sendmail executable path
  -> [String]     -- ^ sendmail command-line options
  -> L.ByteString -- ^ mail message as lazy bytestring
   -> IO ()

Here you want to align :: and -> in the same column position. To do this use the -a flag:

align -a -- '-> ::' < input2.sample

(FYI you need to add the -- argument to prevent the -> string, which starts with a dash, from being parsed as a command option.)

This outputs:

sendmailCustom :: FilePath        -- ^ sendmail executable path
               -> [String]     -- ^ sendmail command-line options
               -> L.ByteString -- ^ mail message as lazy bytestring
               -> IO ()

You can also align the comment (beginning with --) by using a pipeline:

cat input2.sample | align -a -- '-> ::' | align -- '--'

which outputs:

sendmailCustom :: FilePath     -- ^ sendmail executable path
               -> [String]     -- ^ sendmail command-line options
               -> L.ByteString -- ^ mail message as lazy bytestring
               -> IO ()

How to use align in Vim

To use align from Vim, you can select some text, and then use a Vim filter command:

!align '~: @=?'

For common alignment operations, you can make Vim commands and put them in your .vimrc, e.g.:

command! -range AlignHaskellTypeAnnotation :<line1>,<line2>!align '::'
vnoremap <leader>h :AlignHaskellTypeAnnotation<cr>

command! -range AlignHaskellTest :<line1>,<line2>!align '~: @=?'
vnoremap <leader>H :AlignHaskellTest<cr>

Author

Daniel Choi https://github.com/danchoi