# [qm|interpolated-string|]

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Implementation of interpolated multiline string
[QuasiQuoter](https://wiki.haskell.org/Quasiquotation)
that ignores indentation and trailing whitespaces.

Actually it's modification of
[interpolatedstring-perl6](https://github.com/audreyt/interpolatedstring-perl6)
package. I've forked it to implement my own strings I really like.

This implementation based on `qc` from **interpolatedstring-perl6** package
but ignores any indentation, line breaks
(except explicitly written using `\n` char)
and trailing whitespaces.

* 'm' in `qm` means '**M**ultiline'.
* 'n' in `qn` means '**N**o interpolation'.
* 'b' in `qmb`/`qnb` means 'line **B**reaks'.
* 's' in `qms`/`qns` means '**S**paces'.

Write a decoratively formatted string and your
decorative indentation and line breaks wont go to result string,
but when you really need it, you could just escape it using backslash.

## Usage example

```haskell
{-# LANGUAGE QuasiQuotes #-}

import Text.InterpolatedString.QM

main :: IO ()
main = do
  -- Hello, world! Pi is 3.14…
  putStrLn [qms| Hello,
                 world!
                 Pi is {floor pi}.{floor $ (pi - 3) * 100}… |]

  -- Some examples with HTML below to demonstrate the difference
  -- between all of the quasi-quoters.

  let title = "Testing"
      text  = "Some testing text"

  -- <article><h1>Testing</h1><p>Some testing text</p></article>
  putStrLn [qm|
    <article>
      <h1>{title}</h1>
      <p>{text}</p>
    </article>
  |]

  -- <article><h1>{title}</h1><p>{text}</p></article>
  putStrLn [qn|
    <article>
      <h1>{title}</h1>
      <p>{text}</p>
    </article>
  |]

  -- <article> <h1>Testing</h1> <p>Some testing text</p> </article>
  putStrLn [qms|
    <article>
      <h1>{title}</h1>
      <p>{text}</p>
    </article>
  |]

  -- <article> <h1>{title}</h1> <p>{text}</p> </article>
  putStrLn [qns|
    <article>
      <h1>{title}</h1>
      <p>{text}</p>
    </article>
  |]

  -- <article>
  -- <h1>Testing</h1>
  -- <p>Some testing text</p>
  -- </article>
  putStrLn [qmb|
    <article>
      <h1>{title}</h1>
      <p>{text}</p>
    </article>
  |]

  -- <article>
  -- <h1>{title}</h1>
  -- <p>{text}</p>
  -- </article>
  putStrLn [qnb|
    <article>
      <h1>{title}</h1>
      <p>{text}</p>
    </article>
  |]
```

## Tables

### All QuasiQuoters

```
| QuasiQuoter | Interpolation | Indentation | Line breaks          | Trailing whitespaces |
|-------------|---------------|-------------|----------------------|----------------------|
| qm          | ✓             | Removed     | Removed              | Removed              |
| qn          | ✗             | Removed     | Removed              | Removed              |
| qmb         | ✓             | Removed     | Kept                 | Removed              |
| qnb         | ✗             | Removed     | Kept                 | Removed              |
| qms         | ✓             | Removed     | Replaced with spaces | Removed              |
| qns         | ✗             | Removed     | Replaced with spaces | Removed              |
```

### About naming logic

```
| Contains in its name | What means                       | QuasiQuoters |
|----------------------|----------------------------------|--------------|
| m                    | Resolves interpolation blocks    | qm, qmb, qms |
| n                    | Without interpolation            | qn, qnb, qns |
| b                    | Keeps line breaks                | qmb, qnb     |
| s                    | Replaces line breaks with spaces | qms, qns     |
```

## About interpolation blocks

Along with all specifics of any of the quoters (which supports interpolation
blocks, which has `m` in their names) interpolation blocks work different. When
curly bracket (`{`) opens everything inside until it closes (by `}`) is parsed
as bare as possible to be given to
[haskell-src-meta](http://hackage.haskell.org/package/haskell-src-meta)
without any modifications, to be parsed as bare Haskell code.

But you might need use curly brackets inside an interpolation block. I don't
think it would be a good idea, because complicated logic there may cause code
readability issues, but if you're sure you need it then you get it. You just
need to escape closing bracket to prevent interpolation block from closing, like
this: `\}`. I know it could parsed and opening curly brackets inside could be
used to prevent closing by next `}` symbol, but I chose do it this way to
prevent any unobvious tricky behavior (e.g. consider `}` appear inside a string,
`[qm|foo {'x':'}':"y"} bar|]`, how that should be handled?). So I've decided to
not make parser to be very smart, just to follow simple logic. You just need to
explicitly escape every `}` symbol inside that isn't closer of an interpolation
block (you could find an example below).

## About escaping

### Symbols that can be escaped

Backslash is used for escaping these:

  1. `\n` - line break
  2. `\ ` - space (space is supposed to be escaped when you're going to keep
            some part of indentation)
  3. `\↵` - backslash just before end of line cuts off line break
            (makes sense for `qmb`, `qnb`, `qms` and `qns`)
  4. `\{` - opening bracket of interpolation block
            (only for `qm`, `qmb` and `qms`, to prevent interpolation
            and interpret this block as plain text)
  5. `\t` or `\‣` (where `‣` is real tab symbol) - tab (escaping it to keep some
     part of indentation, or if you need tab symbol for some reason,
     escaping real tabs makes sense only for keeping some part of indentation)
  6. `\\` - backslash itself (for situations when you don't want to escape
            other symbols but just want backslash symbol, `\\t`, `\\n`, `\\↵`,
            `\\{`, etc., if backslash doesn't come with any of symbols from
            this list it is interpreted just as backslash symbol, keep in mind
            that `\\\` (without any of symbols from this list after)
            and `\\\\` are producing same result - `\\`)
  7. `\}` - closing bracket inside an interpolation block
            (it works **only** inside opened interpolation block)
            to prevent interpolation block from closing
            (useful to escape records modification)

### Escaping examples

```haskell
[qm| foo\nbar  |] -- "foo\nbar"
[qm| foo\\nbar |] -- "foo\\nbar"
[qm| foo\tbar  |] -- "foo\tbar"
[qm| foo\\tbar |] -- "foo\\tbar"
[qm| foo\‣bar  |] -- "foo\tbar"   (`‣` is real tab symbol)
[qm| foo\\‣bar |] -- "foo\\\tbar" (`‣` is real tab symbol)
[qm| foo\ bar  |] -- "foo bar"
[qm| foo\\ bar |] -- "foo\\ bar"

[qm| foo\
     bar  |] -- "foobar"
[qm| foo\\
     bar  |] -- "foo\\bar"

[qmb| foo\
      bar  |] -- "foobar"
[qmb| foo\\
      bar  |] -- "foo\\\nbar"

[qm| foo\bar    |] -- "foo\\bar"
[qm| foo\\bar   |] -- "foo\\bar"
[qm| foo\\\bar  |] -- "foo\\\\bar"
[qm| foo\\\\bar |] -- "foo\\\\bar"
```

## More examples

```haskell
[qm|   you can escape spaces
     \ when you need them    |]
-- Result: "you can escape spaces when you need them"
```

```haskell
[qm|
        indentation and li
  ne bre
   aks are i
       gno
     red
|]
-- Result: "indentation and line breaks are ignored"
```

```haskell
[qm|  \  You can escape indentation or\n
         line breaks when you need them! \  |]
-- Result: "  You can escape indentation or\nline breaks when you need them!  "
```

```haskell
[qm| Interpolation blocks can be escaped too: {1+2} \{3+4} |]
-- Result: "Interpolation blocks can be escaped too: 3 {3+4}"
```

If you don't need interpolation - just replace `m` to `n` in quasi-quoter name:

```haskell
[qm| foo {1+2} |] -- Result: "foo 3"
[qn| foo {1+2} |] -- Result: "foo {1+2}"

[qms| foo {1+2} |] -- Result: "foo 3"
[qns| foo {1+2} |] -- Result: "foo {1+2}"

[qmb| foo {1+2} |] -- Result: "foo 3"
[qnb| foo {1+2} |] -- Result: "foo {1+2}"
```

That's how you update some record inside interpolation block
(you need to escape closing bracket):

```haskell
{-# LANGUAGE QuasiQuotes #-}
import Text.InterpolatedString.QM (qm)
data Foo = Foo {bar :: Int, baz :: Int} deriving Show
main = let foo = Foo 10 20 in putStrLn [qm| Foo is: {foo {baz = 30\}} |]
-- Foo is: Foo {bar = 10, baz = 30}
```

## Syntax highlighting

### Vim or Neovim

#### "haskell-vim" plugin

If you use [haskell-vim][haskell-vim] plugin (I personally use
[my own fork][my-haskell-vim-fork] which supports `UnicodeSyntax`) just add to
your `.vimrc` or `init.vim` this:

```vim
fu! s:highlight_haskell_qm_interpolation_blocks()
  sy match haskellQMStr "." containedin=haskellQM contained

  sy region haskellQMBlock matchgroup=haskellDelimiter
    \ start="\(^\|\(^\|[^\\]\)\(\\\\\)*\)\@<={" end="}"
    \ contains=TOP,@Spell containedin=haskellQM contained

  sy region haskellQM matchgroup=haskellTH
    \ start="\[qm\(b\|s\)\?|" end="|\]"

  hi def link haskellQMStr String
endf

au FileType haskell cal s:highlight_haskell_qm_interpolation_blocks()
```

## Wanna make a contribution or maintain your own fork?

See [CONTRIBUTING.md][CONTRIBUTING.md].

## Author

Viacheslav Lotsmanov

This library is a heavily rewritten and extended fork of
[interpolatedstring-perl6][fork-origin]
which was originally created by Audrey Tang.

## License

[The Unlicense][LICENSE]

[haskell-vim]: https://github.com/neovimhaskell/haskell-vim
[my-haskell-vim-fork]: https://github.com/unclechu/haskell-vim
[fork-origin]: https://github.com/audreyt/interpolatedstring-perl6/blob/63d91a83eb5e48740c87570a8c7fd4668afe6832/src/Text/InterpolatedString/Perl6.hs

[CONTRIBUTING.md]: https://github.com/unclechu/haskell-qm-interpolated-string/blob/master/CONTRIBUTING.md
[LICENSE]: https://github.com/unclechu/haskell-qm-interpolated-string/blob/master/LICENSE