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lib for running gramcheck and other pipelines + cli; modules for CG→spelling, CG→feedback, tagging blanks

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# Table of Contents

1.  [Description](#org4fcc88a)
2.  [Tools](#org56275a9)
3.  [Install from packages](#org9a6527d)
4.  [Simple build from git on Mac](#org96ee39f)
5.  [Prerequisites](#org6558baf)
    1.  [For just `divvun-suggest` and `divvun-blanktag`](#org52997e2)
    2.  [If you also want `divvun-checker`](#org7916c8e)
    3.  [If you also want `divvun-cgspell`](#orge31ee76)
    4.  [If you also want the Python library](#org494f256)
6.  [Building](#org1e607c1)
7.  [Command-line usage](#org32fa957)
    1.  [`divvun-suggest`](#orgb9f4fb0)
    2.  [`divvun-blanktag`](#org5e9008d)
    3.  [`divvun-cgspell`](#orgb2d7c60)
    4.  [`divvun-checker`](#orge4c3771)
8.  [JSON format](#orge91d3d5)
9.  [Pipespec XML](#org4724bf8)
    1.  [Mapping from XML preferences to UI](#org055a209)
10. [Writing grammar checkers](#org4e0bfc0)
    1.  [XML pipeline specification](#org6bea8af)
    2.  [Simple blanktag rules](#org19dbac0)
        1.  [Troubleshooting](#orgde13873)
    3.  [Simple grammarchecker.cg3 rules](#org0955ce1)
    4.  [More complex grammarchecker.cg3 rules (spanning over several words)](#org6b5053d)
    5.  [Deleting words](#org4d2c8ef)
    6.  [Moving words](#orge2f043f)
    7.  [Alternative suggestions for complex errors altering different parts of the error](#orge26043f)
    8.  [Adding words](#orgb76a5c9)
    9.  [Adding literal word forms, altering existing wordforms](#orge23663a)
    10.  [Including spelling errors](#org26182db)
    11. [How underlines and replacements are built](#orgb25740d)
    12. [Summary of special tags and relations](#orgb55740d)
        1.  [Tags](#org67d1b58)
        2.  [Relations](#orga4550ed)
11. [Troubleshooting](#orge03c2e9)
12. [References / more documentation](#org7a81616)

# Description

Libdivvun is a library for handling Finite-State Morphology and Constraint
Grammar based NLP tools in GiellaLT. The tools are used for tokenisation,
normalisation, grammar-checking and correction, and other NLP tasks.

# Tools

This repository contains the library `libdivvun`, and following
executables:

`divvun-checker`: This program opens a grammar checker pipeline XML
specification and lets you run grammar checking on strings. It can
also open zip files containing the XML and all required language
data. The C++ library `libdivvun` (headers installed to
`$PREFIX/include/divvun/*.hpp`) allows for the same features.

`divvun-suggest`: This program does FST lookup on forms specified as
Constraint Grammar format readings, and looks up error-tags in an XML
file with human-readable messages. It is meant to be used as a late
stage of a grammar checker pipeline.

The main output format of `divvun-suggest` is JSON, although it can
also simply annotate readings in CG stream format.

`divvun-cgspell`: This program spells unknown word forms from
Constraint Grammar format readings, adding them as new readings.

`divvun-blanktag`: This program takes an FST as argument, reads CG
input and uses the FST to add readings to cohorts that match on the
wordform surrounded by the preceding and following blanks. Use cases
include adding error tags that are dependent on spaces before/after,
or tagging the first word after a linebreak or certain formatting.

`divvun-phon`: This program takes FSAs, reads CG input and uses
the FSAs to add phonetic readings to each analysis lines

`divvun-normalise`: This program takes FSAs, reads CG input and uses
the FSAs to normalise the text towards TTS friendlier, read-out forms

There are also some helper programs for validating XML
(`divvun-validate-suggest`, `divvun-validate-pipespec`,
`divvun-gen-xmlschemas`) and for generating shell scripts from
pipeline specifications (`divvun-gen-sh`).

# Install from packages

Tino Didriksen has kindly packaged this as both `.deb` and `.rpm`.

For `.deb` (Debian, Ubuntu and derivatives), add the repo and install
the package with:

wget https://apertium.projectjj.com/apt/install-nightly.sh
    sudo bash install-nightly.sh
    sudo apt install divvun-gramcheck

For `.rpm` (openSUSE, Fedora, CentOS and derivatives), add the repo
and install the package with:

wget https://apertium.projectjj.com/rpm/install-nightly.sh
    sudo bash install-nightly.sh
    sudo dnf install divvun-gramcheck

(See also the [deb build logs](https://apertium.projectjj.com/apt/logs/divvun-gramcheck/) and [rpm build status](https://build.opensuse.org/package/show/home:TinoDidriksen:nightly/divvun-gramcheck).)

# Simple build from git on Mac

There is a script that will download prerequisites and compile and
install for Mac.

You don't even need to checkout this repository; just run:

curl https://raw.githubusercontent.com/divvun/divvun-gramcheck/master/scripts/mac-build | bash

and enter your `sudo` password when it asks you to.

It does not (yet) enable `divvun-checker`, since that has yet more
dependencies. It assumes you've got `xmllint` installed.

# Prerequisites

*Note: Mac users probably just want to follow the steps in [Simple
build from git on Mac](#org96ee39f).*

This section lists the prerequisites for building the various tools in
this package.

## For just `divvun-suggest` and `divvun-blanktag`

-   gcc >=5.0.0 with libstdc++-5-dev (or similarly recent version of
    clang, with full C++17 support)
-   libxml2-utils (just for xmllint)
-   utfcpp (also known as utf8cpp)
-   libhfst >=3.12.2
-   libpugixml >=1.7.2 (optional)

Tested with gcc-5.2.0, gcc-5.3.1 and clang-703.0.29. On Mac OS X, the
newest XCode includes a modern C++ compiler.

If you can't easily install libpugixml, you can run
[scripts/get-pugixml-and-build](scripts/get-pugixml-and-build) which will download libpugixml into this
directory, build that (with cmake) and configure this program to use
that library. Alternatively, you can run ./configure with
`--disable-xml` if you don't care about human-readable error messages.

## If you also want `divvun-checker`

Tested with gcc-5.2.0, gcc-5.3.1 and clang-703.0.29. On Mac OS X, the
newest XCode includes a modern C++ compiler.

Now when building, pass `--enable-checker` to configure.

## If you also want `divvun-cgspell`

-   hfst-ospell-dev >=0.4.5 (compiled with either libxml or tinyxml)

You can pass `--enable-cgspell` to `./configure` if you would like to
get an error if any of the `divvun-cgspell` dependencies are missing.

## If you also want the Python library

The Python 3 library is used by the LibreOffice plugin. It will build
if it finds both of:

-   SWIG >=3.0 (install `python-swig` if you're using MacPorts)
-   Python >=3.0

You can pass `--enable-python-bindings` to `./configure` if you would
like to get an error if any of the `divvun-python-bindings`
dependencies are missing.

# Building

./autogen.sh
    ./configure --enable-checker  # or just "./configure" if you don't need divvun-checker
    make
    make install # with sudo if you didn't specify a --prefix to ./configure

On OS X, you may have to do this:

sudo port install pugixml
    export CC=clang CXX=clang++ "CXXFLAGS=-std=gnu++11 -stdlib=libc++"
    ./autogen.sh
    ./configure  LDFLAGS=-L/opt/local/lib --enable-checker
    make
    make install # with sudo if you didn't specify a --prefix to ./configure

# Command-line usage

## `divvun-suggest`

`divvun-suggest` takes two arguments: a generator FST (in HFST
optimised lookup format), and an error message XML file (see [the one
for North Saami](https://gtsvn.uit.no/langtech/trunk/langs/sme/tools/grammarcheckers/errors.xml) for an example), with input/output as stdin and
stdout:

src/divvun-suggest --json generator-gt-norm.hfstol errors.xml < input > output

More typically, it'll be in a pipeline after various runs of `vislcg3`:

echo words go here | hfst-tokenise --giella-cg tokeniser.pmhfst | … | vislcg3 … \
      | divvun-suggest --json generator-gt-norm.hfstol errors.xml

## `divvun-blanktag`

`divvun-blanktag` takes one argument: an FST (in HFST
optimised lookup format), with input/output as stdin and
stdout:

src/divvun-blanktag analyser.hfstol < input > output

More typically, it'll be in a pipeline after `cg-mwesplit`:

echo words go here | hfst-tokenise … | … | cg-mwesplit \
      | src/divvun-blanktag analyser.hfstol < input > output

See the file [test/blanktag/blanktagger.xfst](test/blanktag/blanktagger.xfst) for an example blank
tagging FST (the other files in [test/blanktag](test/blanktag) show test input and
expected output, as well as how to compile the FST).

## `divvun-cgspell`

`divvun-cgspell` takes options similar to [hfst-ospell](https://github.com/hfst/hfst-ospell/). You can give it
a single zhfst speller archive with the `-a` option, or specify
unzipped error model and lexicon with `-m` and `-l` options.

There are some options for limiting suggestions too, see
`--help`. You'll probably want to use `--limit` at least.

src/divvun-cgspell --limit 5 se.zhfst < input > output

More typically, it'll be in a pipeline before/after various runs of `vislcg3`:

You can also use it with unzipped, plain analyser and error model, e.g.

src/divvun-cgspell --limit 5 -l analyser.hfstol -m errmodel.hfst < input > output

## `divvun-checker`

`divvun-checker` is an example command-line interface to `libdivvun`.
You can use it to test a `pipespec.xml` or a zip archive containing
both the pipespec and langauge data, e.g.

$ divvun-checker -a sme.zhfst
    Please specify a pipeline variant with the -n/--variant option. Available variants in archive:
    smegram
    smepunct
    
    $ echo ballat ođđa dieđuiguin | src/divvun-checker -a sme.zhfst -n smegram
    {"errs":[["dieđuiguin",12,22,"msyn-valency-loc-com","Wrong valency or something",["diehtukorrekt"]]],"text":"ballat ođđa dieđuiguin"}
    
    $ divvun-checker -s pipespec.xml
    Please specify a pipeline variant with the -n/--variant option. Available variants in pipespec:
    smegram
    smepunct
    
    $ echo ballat ođđa dieđuiguin | src/divvun-checker -s pipespec.xml -n smegram
    {"errs":[["dieđuiguin",12,22,"msyn-valency-loc-com","Wrong valency or something",["diehtukorrekt"]]],"text":"ballat ođđa dieđuiguin"}

When using the `-s/--spec pipespec.xml` option, relative paths in the
pipespec are relative to the current directory.

See the `test/` folder for an example of zipped archives.

See the [examples folder](examples/using-checker-lib-from-cpp) for how to link into libdivvun and use
it as a library, getting out either the JSON-formatted list of errors,
or a simple [data structure](src/checkertypes.hpp) that contains the same information as the
JSON. The next section describes the JSON format.

# JSON format

The JSON output of `divvun-suggest` is meant to be sent to a client
such as <https://github.com/divvun/divvun-webdemo>. The current format
is:

{errs:[[str:string, beg:number, end:number, typ:string, exp:string, [rep:string]]], text:string}

The string `text` is the input, for sanity-checking.

The array-of-arrays `errs` has one array per error. Within each
error-array, `beg/end` are offsets in `text`, `typ` is the (internal)
error type, `exp` is the human-readable explanation, and each `rep` is
a possible suggestion for replacement of the text between `beg/end` in
`text`.

The index `beg` is inclusive, `end` exclusive, and both indices are
based on a UTF-16 encoding (which is what JavaScript uses, so e.g. the
emoji "🇳🇴" will increase the index of the following errors by 4).

Example output:

{
      "errs": [
        [
          "badjel",
          37,
          43,
          "lex-bokte-not-badjel",
          "\"bokte\" iige \"badjel\"",
          [
            "bokte"
          ]
        ]
      ],
      "text": "🇳🇴sáddejuvvot báhpirat interneahta badjel.\n"
    }

# Pipespec XML

The `divvun-checker` program and `libdivvun` (`divvun/checker.hpp`)
API has an XML format for specifying what programs go into the checker
pipelines, and metadata about the pipelines.

A `pipespec.xml` defines a set of grammar checker (or really any text
processing) pipelines.

There is a main language for each pipespec, but individual pipelines
may override with variants.

Each pipeline may define certain a set of mutually exclusive (radio
button) preferences, and if there's a `<suggest>` element referring to
an `errors.xml` file in the pipeline, error tags from that may be used
to populate UI's for hiding certain errors.

## Mapping from XML preferences to UI

The mapping from preferences in the XML to a user interface should be
possible to do automatically, so the UI writer doesn't have to know
anything about what preferences the pipespec defines, but can just ask
the API for a list of preferences.

Preferences in the UI are either checkboxes [X] or radio buttons (\*).

We might for example get the following preferences UI:

(*) Nordsamisk, Sverige
    ( ) Nordsamisk, Noreg
    …
    [X] Punctuation
        (*) punktum som tusenskilje
        ( ) mellomrom som tusenskilje
    [-] Grammar errors
        [X] ekteordsfeil
        [ ] syntaksfeil

Here, the available languages are scraped from the pipespec.xml
using `//pipeline/@language`.

A language is selected, so we create a Main Category of error types from

pipespec.xml //[@language=Sverige|@language=""]/prefs/@type
    pipespec.xml //pipeline[@language=Sverige|@language=""]/@type
    errors.xml   //default/@type
    errors.xml   //error/@type

in this case giving the set { Punctuation, Grammar errors }.

One Main Category type is Punctuation; the radio buttons under
this main category are those defined in

pipespec.xml //prefs[@type="Punctuation"]

The other Main Category type is Grammar errors; maybe we didn't have anything
in

pipespec.xml //prefs[@type="Grammar errors"]

but there are checkboxes for errors that we can hide in

errors.xml //defaults/default/title

It should be possible for the UI to hide which underlying
`<pipeline>`'s are chosen, and only show the preferences (picking a
pipeline based on preferences). But there is an edge case: Say the
pipe named smegram<sub>SE</sub> with language sme<sub>SE</sub> and main type "Grammar
errors" has a

pref[@type="Punctuation"]

and there's another pipe named smepunct with main type "Punctuation".
Now, assuming we select the language sme<sub>SE</sub>, we'll never use smepunct,
since smegram defines error types that smepunct doesn't, but not the
other way around. Hopefully this is not a problem in practice.

# Writing grammar checkers

Grammar checkers written for use in `libdivvun` consist of a
pipeline, at a high level typically looking like:

tokenisation/morphology | multiword handling | disambiguation | error rules | generation

There are often other modules in here too, e.g. for adding spelling
suggestions, annotating valency, disambiguation and splitting
multiwords, or annotating surrounding whitespace.

Below we go through some of the different parts of the checker, using
the Giellatekno/Divvun North Sámi package (from
<https://victorio.uit.no/langtech/trunk/langs/sme/>) as an example.

## XML pipeline specification

Each grammar checker needs a pipeline specification with all the
different modules and their data files in order. This is written in a
file `pipespec.xml`, which should follow the . Each such
file may have several `<pipeline>` elements (in case there are
alternative pipeline variants in your grammar checker package), with a
name and some metadata.

Here is the `pipespec.xml` for North Sámi:

This is what happens when text is sent through the `smegram` pipeline:

-   First, `<tokenize>` turns plain text into morphologically analysed
    tokens, using an FST compiled with `hfst-pmatch2fst`. These tokens
    may be ambiguous both wrt. to morphology and tokenisation.
-   Then, a `<cg>` module adds valency tags to readings, enriching the
    morphological analysis with context-sensitive information on
    argument structure.
-   Another `<cg>` module disambiguates cohorts that are ambiguous
    wrt. tokenisation, like multiwords and punctuation.
-   The `<mwesplit>` module splits now-disambiguated multiwords into
    separate tokens.
-   Then `<blanktag>` adds some tags to readings based on the
    surrounding whitespace (or other types of non-token
    blanks/formatting), using an FST which matches sequences of
    blank–wordform–blank.
-   The `<cgspell>` module adds readings with spelling suggestions to
    unknown words. The suggestions appear as wordform-tags.
-   Then a `<cg>` disambiguator, with rules modified a bit to let
    through more errors.
-   The main `<cg>` grammar checker module can now add error tags to
    readings, as well as new readings for generating suggestions, or
    special tags for deleting words or expanding underlines (and, as in
    the other `<cg>` modules, we can use the full range of CG features
    to add information that may be helpful in these tasks, such as
    dependency annotation and semantic role analysis)
-   Finally, `<suggest>` uses a generator FST to turn suggestion
    readings into forms, and an XML file of error descriptions to look
    up error messages from the tags added by the `<cg>` grammar checker
    module. These are used to output errors with suggestions, as well as
    readable error messages and the correct indices for underlines.

The program `divvun-gen-sh` in this package creates shell scripts from
the specification that you can use to test your grammar checker. In
the North Sámi checker, these should appear in
`tools/grammarcheckers/modes` when you type `make`, but you can also
create a single script for the above pipeline manually. If we do
`divvun-gen-sh -s pipespec.xml -n smegram > test.sh` with the above
XML, `test.sh` will contain something like

#!/bin/sh
    
    hfst-tokenise -g '/home/me/gtsvn/langs/sme/tools/grammarcheckers/tokeniser-gramcheck-gt-desc.pmhfst' \
     | vislcg3 -g '/home/me/gtsvn/langs/sme/tools/grammarcheckers/valency.bin' \
     | vislcg3 -g '/home/me/gtsvn/langs/sme/tools/grammarcheckers/mwe-dis.bin' \
     | cg-mwesplit \
     | divvun-blanktag '/home/me/gtsvn/langs/sme/tools/grammarcheckers/analyser-gt-whitespace.hfst' \
     | divvun-cgspell '/home/me/gtsvn/langs/sme/tools/grammarcheckers/errmodel.default.hfst' '/home/me/gtsvn/langs/sme/tools/grammarcheckers/acceptor.default.hfst' \
     | vislcg3 -g '/home/me/gtsvn/langs/sme/tools/grammarcheckers/disambiguator.bin' \
     | vislcg3 -g '/home/me/gtsvn/langs/sme/tools/grammarcheckers/grammarchecker.bin' \
     | divvun-suggest '/home/me/gtsvn/langs/sme/tools/grammarcheckers/generator-gt-norm.hfstol' '/home/me/gtsvn/langs/sme/tools/grammarcheckers/errors.xml'

We can send words through this pipeline with `echo "words here" | sh
test.sh`.

Using `divvun-gen-sh` manually like this is good for checking if
you've written your XML correctly, but if you're working within the
Giellatekno projects, you'll typically just type `make` and use the
scripts that end up in `modes`.

$ ls modes

in `tools/grammarcheckers` to list all the scripts. These contain not
just the full pipeline (for every `<pipeline>` in the XML), but also
"debug" versions that are chopped off at various points (with numbers
to show how far they go), as well as versions with CG rule tracing
turned on. So if you'd like to check up until disambiguation, before
the `grammarchecker` CG, you'd do something like

echo "words go here" | sh modes/trace-smegram6-disam.mode

## Simple blanktag rules

The `divvun-blanktag` program will tag a cohort with a user-specified
tag if it finds a match on the input wordform and its surrounding
blanks.

The wordform includes the CG wordform delimiters

and

The surrounding blanks do *not* include the start-of-line colon. The
rule file is an FST with blank-wordform-blank on the input side, and
the tag on the output-side, typically written in the XFST regex
format.

As an example (with spaces changed to underscores for readability), if
the `input.txt` contains

:_
    "<)>"
            ")" RPAREN @EOP
            ")" RPAREN @EMO
    "<.>"
            "." PUNCT
    :\n
    :\n

then `divvun-blanktag` will try to match twice, first on the string

_"<)>"

then on the string

"<.>"\n\n

If the rule file `ws.regex` (here in XFST regex format) contains

[ {_} {"<)>"} ?* ]:[%<spaceBeforeParenEnd%>]

then we will get

hfst-regexp2fst --disjunct ws.regex | hfst-fst2fst -O -o ws.hfst
    divvun-blanktag ws.hfst < input.txt

:_
    "<)>"
    	")" RPAREN @EOP <spaceBeforeParenEnd>
    	")" RPAREN @EMO <spaceBeforeParenEnd>
    "<.>"
    	"." PUNCT
    :\n
    :\n

The matching goes from the start of the preceding blank, across the
wordform and to the end of the following blank. In this input, there
was no blank following the right-parens, so the rule could just as
well have been

[ {_} {"<)>"} ]:[%<spaceBeforeParenEnd%>]

– this would **require** that there is no following blank. However, if
you want it to also match the input

:_
    "<)>"
            ")" RPAREN @EOP
            ")" RPAREN @EMO
    :\n

then you need the final match-all `?*`.

### Troubleshooting

If you get

terminate called after throwing an instance of 'FunctionNotImplementedException'                                                [68/660]
    Aborted (core dumped)

check how you compiled the HFST file – it should be in unweighted HFST
optimized lookup format.

## Simple grammarchecker.cg3 rules

In our North Sámi checker, the

file is created with from the source file
`$GTHOME/langs/sme/tools/grammarcheckers/grammarchecker.cg3`, which
adds error tags and suggestion-readings.

A simple rule looks like:

ADD:msyn-hallan (&real-hallan) TARGET (Imprt Pl1 Dial/-KJ) IF (0 HALLA-PASS-V) (NEGATE *1 ("!")) ;

This simply adds an error tag `real-hallan` to words that are tagged
`Imprt Pl1 Dial/-KJ` and match the context conditions after the
`IF`. This will put an underline under the word in the user
interface. If `errors.xml` in the same folder has a nice description
for that tag, the user will see that description in the user
interface.

We can add a suggestion as well with a `COPY` rule:

COPY:msyn-hallan (Inf SUGGEST) EXCEPT (Imprt Pl1 Dial/-KJ) TARGET (Imprt Pl1 Dial/-KJ &real-hallan) ;

This creates a new reading where the tags `Imprt Pl1 Dial/-KJ` have
been changed into `Inf SUGGEST` (and other tags are unchanged). The
`SUGGEST` tag is necessary to get `divvun-suggest` (the `<suggest>`
module) to try to generate a form from that reading. It is smart
enough to skip things like weights, tracing and syntax tags when
trying to suggest, but all morphological tags need to be correct and
in the right order for generation to work.

## More complex grammarchecker.cg3 rules (spanning over several words)

The error is considered to have a central part and one or more less
central parts (parts here being CG cohorts).

The central part needs the error tag, e.g. `&real-hallan` in
the above simple example.

If there are several different ways of correcting an error, you may
also need to add "co-error tags" to the non-central parts to
disambiguate the replacements – see the below section on [Alternative
suggestions for complex errors altering different parts of the
error](#orgb76a5c9) for details on this.

The non-central parts need to be referred to by a relation named
`LEFT` or `RIGHT` or `DELETE` from the central part, if all all parts
are to be underlined as one error. The words can be adjacent. If there
are words in between that are not part of the error, they are still
underlined.

In the first line of the following example only "soaitá" and "boađán"
are part of the error and are underlined. However, if "mun" ("I") is
inserted in between then it is also underlined.

Mun soaitá boađán. `Maybe I come.'
    Soaitá mun boađán. `Maybe I come.'

You can refer to the word form of the "central" cohort of the error
using `$1` in errors.source.xml, e.g.

<description xml:lang="en">The word "$1" seems to be in the wrong case.</description>

You can refer to the word form of the first correction / suggestion
using `€1` in errors.source.xml, e.g.

<description xml:lang="en">Please don't write "$1", it sounds much nicer if you use "€1" instead.</description>

- $1 - reference to error
    - €1 - reference to suggestion

---

To refer to other words (e.g. `co&`-errors), you add relations named
`$2` and so on:

ADDRELATION ($2) Ess TO (*-1 ("dego" &syn-not-dego) BARRIER Ess);

which you can refer to just like with `$1`:

<title xml:lang="en">there should not be "$2" if "$1" is essive</title>

## Deleting words

If you want to delete a word from a CG rule, it's typically enough to
add an error tag to the word you want to *keep*, and add a relation
`DELETE1` to the word you want to delete. This will make an underline
that covers both those words, where the suggestion is the same string
without the target of the `DELETE1` relation.

ADD (&one-word-too-many) KeepThisWord;
    ADDRELATION (DELETE1 $2) KeepThisWord TO (-1 DeleteThisWord);

The cohort matching `KeepThisWord` is now the central one of the
error, so if e.g. `errors.xml` uses templates like

Don't use "$2" before using "$1"

the word form of `KeepThisWord` will be substituted for `$1`.

A real example from North Sámi is the error "dego lávvomuorran" where
we want to delete the word "dego" from the suggestion and keep
"lávvomuorran" (the central word, `$1` in `errors.xml`):

ADD (&syn-not-dego)      TARGET Ess IF (-1 ("dego")) ;
    ADDRELATION (DELETE1 $2) TARGET (&syn-not-dego) TO (-1 ("dego"));

You may delete more words from the same cohort using `DELETE2` etc.

In South Sámi sometimes phrasal verbs are used (due to a literal
translation from Scandinavian languages) where the verb alone already
expresses the concept. This is the case for "tjuedtjelh bæjjese"
(verb + adverb) meaning "stand.up up". With the following rule we
first annotate the error and then delete the adverb "bæjjese".

ADD (&syn-delete-adv-phrasal-verb) TARGET (V) IF (0 ("tjuedtjielidh") OR ("fulkedh")) (*0 ("bæjjese") BARRIER (*) - Pcle) ;
    ADD (&syn-delete-adv-phrasal-verb) TARGET (Adv) IF (0 ("bæjjese")) (*0 ("tjuedtjielidh") OR ("fulkedh") BARRIER (*) - Pcle) ;

ADDRELATION (DELETE1) (V &syn-delete-adv-phrasal-verb) TO (*0 (Adv &syn-delete-adv-phrasal-verb) BARRIER (*) - Pcle) ;

If you want to delete the "central" error-marked word itself, you can
add a relation from the cohort to itself:

ADD (&superfluous) ("prior") IF (1 ("experience")) ;
    ADDRELATION (DELETE1) TARGET (&superfluous) TO (0 (*));

There is also a shorthand for this situation, the *tag* `DELETE` has
the same effect as a DELETE *relation* to itself:

ADD (DELETE) TARGET (&superfluous);

## Moving words

This `DELETE` tag mentioned above is also useful when moving a word as
part of a suggestion – to do that, we *copy* the cohort, placing one
copy (tagged `ADDED`) in the correct position, and marking the
original as `DELETE`. As an example, let's correct the Norwegian word
order from

I dag eg til skulen gjekk.

I dag gjekk eg til skulen.

We'll target the verb "gjekk", copy it and place the new copy back
before the subject (after the adverb), and mark the other copy for
deletion:

WITH fv IF
            (*-1 Adv LINK 1 @Subj) # The word found by this context condition is available as _C1_
    {
       ADD (DELETE &syn-wordorder) (*) ;

COPYCOHORT (ADDED co&syn-wordorder) # These tags will be added to the new copy
          EXCEPT (DELETE &syn-wordorder)    # We don't include the error tag or DELETE in the new copy
          TARGET (*)                   # Copy from the main WITH target
          TO BEFORE (jC1 (*))          # The copy ends up before the first WITH context
          ;

# Link the words so they're treated as part of the same error squiggle:
       ADDRELATION (LEFT) (*) TO (jC1 (*));
    };

## Alternative suggestions for complex errors altering different parts of the error

Sometimes you have several possible suggestions on the same word,
which might partially overlap. For example, the simple deletion
example from above might also have an alternative interpretation where
instead of deleting the word "dego" to the left, we should change the
case of the word "lávvomuorran" from essive to nominative case:

ADD (&syn-dego-nom) TARGET Ess IF (-1 ("dego"));
    COPY (Sg Nom SUGGEST) EXCEPT (Ess) TARGET (&syn-dego-nom) ;

Here we want to keep the suggestions for `&syn-dego-nom` separate from
the suggestions for `&syn-not-dego` – in particular, we don't want to
include a suggestion where we *both* delete and change cases at the
same time. But if we use the above rules, CG gives us this output:

"<dego>"
            "dego" CS @CNP ID:11
    :
    "<lávvomuorran>"
             "lávvomuorra" N Ess @COMP-CS< &syn-not-dego ID:12 R:DELETE1:11
             "lávvomuorra" N Sg Nom @COMP-CS< &syn-dego-nom ID:12 R:DELETE1:11 SUGGEST

Notice how the DELETE relation is on both readings, and also how how
the relation target id (`11`) refers to a cohort, not a reading of a
cohort. There is no way from this output to know that "dego" should
not also be deleted from the `SUGGEST` reading.

So when there are such multiple alternative interpretations for errors
spanning multiple words, the less central parts ("dego" above) also
need a matching error tag to say which error tag goes with which
non-central or suggestion reading. We often use the `co&` prefix
instead of `&` which indicates that this is not the main reading of
the complex error:

ADD (co&syn-not-dego) ("dego") IF (1 (&syn-not-dego));

Without `co&syn-not-dego`, we would suggest deleting "dego" in the
suggestions for `&syn-dego-nom` too.

By using `co&error-tags`, we can have multiple alternative
interpretations of an error, while avoiding generating bad
combinations. In the following case:

Soaitá boađán.

there are two possible corrections:

Soaittán boahtit.
    Kánske boađán.

The alternative corrections have different central parts of the error.
In the first case both parts are changed. The first part ("soaitá"
3.Sg.) is changed to "soaittán" (1.Sg.) based on the person and number
of the second word ("boađán" 1.Sg.). Subsequently "boađán" (1.Sg.) is
changed to "boahtit" (infinitive). Alternatively, only the first part
is changed and the second part remains unchanged. In this case we can
change the "soaitá" (3.Sg.) to the adverb "kánske".

As usual, this requires `SUGGEST` readings for the parts that are two
be changed, and one unique error tag for each interpretation, ie.
`&msyn-kánske` for the "Kánske boađán" correction and
`&msyn-fin_fin-fin_inf` for the "Soaittán boahtit" correction.

We also need relations `LEFT/RIGHT` from the central cohort carrying
the error tag to ensure both words are underlined. Again, if we say
that the correction "boahtit" has a relation to the correction
"Soaittán", CG only knows that there's a relation between the words,
not between the individual readings. In order to match
readings-to-readings, we use the (co-)error tags to match up. If we
chose the first word (input form "Soaitá") to be the central cohort,
and had the error tag `&msyn-kánske` on the suggestion for "Kánske",
then we would add a relation `RIGHT` to the second word (input form
"boađán") and add the co-error tag `co&msyn-kánske` to the correct
reading of that word (in this case the reading that does *not* suggest
a change). So the CG output after grammar checker should contain:

```
"<Soaitá>"
	"soaitit" V IV Ind Prs Sg3 &syn-soahtit-vfin+inf   ID:2 R:RIGHT:3
	"soaitit" V IV Ind Prs Sg1 &syn-soahtit-vfin+inf   ID:2 R:RIGHT:3 SUGGEST
	"kánske"  Adv              &syn-kánske             ID:2 R:RIGHT:3 SUGGEST
: 
"<boađán>"
	"boahtit" V IV Ind Prs Sg1                         ID:3
	"boahtit" V IV Ind Prs Sg1 co&syn-kánske           ID:3 SUGGEST
	"boahtit" V IV Inf         co&syn-soahtit-vfin+inf ID:3 SUGGEST
```

By adding `co&msyn-kánske` etc., we avoid generating silly suggestion
combinations like *"Kánske boahtit" or *"Soaittán boađán".

Another example:

Dåaktere veanhta dïhte aktem aajla-hirremem åtneme, dan åvteste tjarke svæjmadi jïh
    {ij mujhti} satne lij vaedtsieminie skuvleste gåatan.

In this sentence in South Sámi there are two alternative suggestions:

-   one regarding the second cohort only &#x2013; `mujhti > mujhtieh`
-   the other one regarding both cohorts &#x2013; `ij mujhti > idtji mujhtieh`

Here too, we need to ensure that there are `co&errortags` to match
relations to readings.

Often we change all `&error` tags to `co&error` tags at the end of a
rule section:

```
SUBSTITUTE (&syn-kánske) (co&syn-kánske) TARGET (SUGGEST) ;
MAP:LOCK_READING (SUGGEST) (SUGGEST); # avoid rules looping
```

This is so we can have a
`LIST Errors = &syn-kánske &syn-soahtit-vfin+inf &etc; `
that will not match the suggestions (the
suggestions are correct, so they should not be matched by the `Errors`
set).

## Avoiding mismatched words in multiple suggestions on ambiguous readings

In the sentence "Sámegiellaåhpadus vatteduvvá skåvlåjn 7 fylkajn ja aj gålmån priváhta skåvlåjn." from Lule Saami, the "7 fylkajn" should either be "7:n fylkan" (both words Sg Ine, error tag &msyn-numphrase-sgine) or "7:jn fylkajn" (both words Sg Com, error tag &msyn-numphrase-sgcom). The erroneous input looks like

```
"<7>"
        "7" Num Arab Sg Nom
        "7" Num Arab Sg Ine Attr
        "7" Num Arab Sg Ill Attr
        "7" Num Arab Sg Gen
        "7" Num Arab Sg Ela Attr
        "7" A Arab Ord Attr CLBfinal
:
"<fylkajn>"
        "fylkka" v1 N Sem/Org Sg Com
        "fylkka" v1 N Sem/Org Pl Ine
:
```

on the way into the grammar checker. For each error tag, we add, copy and substitute, e.g.

```
ADD (&msyn-numphrase-sgcom) TARGET (Num Sg Gen) OR (Num Pl Nom) OR (Num Sg Nom) OR (Num Sg Com) OR ("moadda" Indef Acc) OR (Num Arab) IF …
# and other add rules
COPY (Sg Com SUGGEST) EXCEPT (Sg Com) OR (Pl Ine) TARGET (&msyn-numphrase-sgcom) ;
SUBSTITUTE (&msyn-numphrase-sgcom) (co&msyn-numphrase-sgcom) TARGET (SUGGEST);
```

The error is ambiguous, with two possible suggestions. We want to keep
these apart, but when CG runs the rule section for the second time,
the `ADD` rule for the `sgine` suggestion may land on the reading that
was copied in from the `sgcom` suggestion (now substituted to
`co&msyn-numphrase-sgcom`), mixing the error tags:

```
        "7" Num Arab co&msyn-numphrase-sgcom Sg Ine SUGGEST co&msyn-numphrase-sgine
```
This will lead to mismatched suggestions like "*7:n fylkajn".

To prevent this, we can take advantage of the fact that Constraint
Grammar will not `ADD` anything to a reading that has had a `MAP` rule
applied. We can do this right after the SUBSTITUTE rule:

```diff
 ADD (&msyn-numphrase-sgcom) TARGET (Num Sg Gen) OR (Num Pl Nom) OR (Num Sg Nom) OR (Num Sg Com) OR ("moadda" Indef Acc) OR (Num Arab) IF …
 # and other add rules
 COPY (Sg Com SUGGEST) EXCEPT (Sg Com) OR (Pl Ine) TARGET (&msyn-numphrase-sgcom) ;
 SUBSTITUTE (&msyn-numphrase-sgcom) (co&msyn-numphrase-sgcom) TARGET (SUGGEST);
+MAP:LOCK_READING (SUGGEST) (SUGGEST);
```

## Adding words

To add a word as a suggestion, use `ADDCOHORT`, adding both reading
tags (lemma, part-of-speech etc.), a wordform tag (including a space)
and `ADDED` to mark it as something that didn't appear in the input;
and then a `LEFT` or `RIGHT` relation from the central cohort of the
error to the added word:

ADD (&msyn-valency-go-not-fs) IF (…);
    ADDCOHORT ("<go >" "go" CS ADDED &msyn-valency-go-not-fs) BEFORE &msyn-valency-go-not-fs;
    ADDRELATION (LEFT) (&msyn-valency-go-not-fs) TO (-1 (ADDED)) ;

Because of `ADDED`, `divvun-suggest` will treat this as a non-central
word of the error (just like with `co&` tags).

Note that we include the space in the wordform, and we put it at the
*end* of the wordform. This is because vislcg3 always adds new cohorts
*after* the blank of the preceding cohort. In some cases, e.g. with
punctuation, we want the new cohort to come before the blank of the
preceding cohort; then we use the tag `ADDED-BEFORE-BLANK`, and
`divvun-suggest` will ensure it ends up in the right place, e.g.:

ADD:punct-rihkku (&punct-rihkku) TARGET (Inf) IF (-1 Inf LINK -1 COMMA LINK -1 Inf …);
    ADDCOHORT:punct-rihkku ("<,>" "," CLB ADDED-BEFORE-BLANK &punct-rihkku) BEFORE (V &punct-rihkku) IF …;
    ADDRELATION (LEFT) (&punct-rihkku) TO (-1 (ADDED-BEFORE-BLANK)) ;

will give a suggestion that covers the space before the infinitive.

## Adding literal word forms, altering existing wordforms

Say you want to tag missing spaces after punctuation. You've added a
rule like

[ ?* {"<,>"} ]:[%<NoSpaceAfterPunctMark>]

to your whitespace-analyser.regex (used by `divvun-blanktag`) and the
input to the grammarchecker CG is now

"<3>"
            "3" Num Arab Sg Loc Attr @HNOUN
            "3" Num Arab Sg Nom @HNOUN
            "3" Num Arab Sg Ill Attr @HNOUN
    "<,>"
            "," CLB <NoSpaceAfterPunctMark>
    "<ja>"
            "ja" CC @CNP

Then you can first of all turn that blanktag tag into an error tag with

ADD (&no-space-after-punct-mark) (<NoSpaceAfterPunctMark>);

Now, we could just suggest a wordform on the comma and call it a day:

COPY ("<, >"S SUGGESTWF) TARGET ("," &no-space-after-punct-mark) ;

but that will

1.  only work on commas, and
2.  be a tiny underline, hard to click for users

Instead, let's extend the underline to the following word:

ADD (co&no-space-after-punct-mark)
        TARGET (*)
        IF (-1 (<NoSpaceAfterPunctMark>))
        ;
    ADDRELATION (RIGHT) (&no-space-after-punct-mark)
        TO (1 (co&no-space-after-punct-mark))
        ;

Every error needs a "central" cohort, even if it involves several
words; this is important in order to get error messages to show
correctly. It doesn't matter which one you pick, as long as you pick
one. Here we've picked the comma to be central, while the following
word is a "link" word. In the above rules,

-   The `co&` tag says that the following word is just a part of the
    error, not the central cohort.
-   The `RIGHT` relation says that this is one big error, not two
    separate ones.

We don't have to change the SUGGESTWF reading – `divvun-suggest` knows
how to extend the underline.

Now the output is

"<3>"
            "3" Num Arab Sg Loc Attr @HNOUN
            "3" Num Arab Sg Nom @HNOUN
            "3" Num Arab Sg Ill Attr @HNOUN
    "<,>"	,ja	→	, ja
            "," CLB <NoSpaceAfterPunctMark> &no-space-after-punct-mark ID:3 R:RIGHT:4
            "," CLB <NoSpaceAfterPunctMark> "<, >" &no-space-after-punct-mark SUGGESTWF ID:3 R:RIGHT:4
    "<ja>"
            "ja" CC @CNP co&no-space-after-punct-mark ID:4

or, in JSON format:

{
      "errs": [
        [
          ",ja",
          4,
          7,
          "no-space-after-punct-mark",
          "no-space-after-punct-mark",
          [
            ", ja"
          ]
        ]
      ],
      "text": "ja 3,ja"
    }

This looks pretty good, except the error tag is listed twice. The
second entry is actually supposed to contain a human-readable error
message, but `errors.xml` contains no entry for this tag. Let's add it:

<error id="no-space-after-punct-mark">
      <header>
        <title xml:lang="en">Missing space</title>
      </header>
      <body>
        <description xml:lang="en">There is no space after the punctuation mark "$1"</description>
      </body>
    </error>

(In Giellatekno's setup, this goes in `errors.source.xml`, which is
compiled to `errors.xml`.)

Now we get:

{
      "errs": [
        [
          ",ja",
          4,
          7,
          "no-space-after-punct-mark",
          "Missing space",
          [
            ", ja"
          ]
        ]
      ],
      "text": "ja 3,ja"
    }

which should end up as a nice error message, suggestion and
underline in the UI.

## Creating suggestions using regex capture groups

Some rules have suggestions like `VSTR:"$1$2"S` along with regex
matches like `(0 ("<(.*)>"r) LINK -1 ("<(.*)>"r))` this uses VISL
CG3's [variable strings / varstrings](http://beta.visl.sdu.dk/cg3/chunked/tags.html#variable-strings)
to create wordform suggestion from two regular expression strings
matching the wordforms of the two cohorts. Note that the `$1` and `$2`
refer to the first and second regex groups as they appear in the rule,
not as they appear in the sentence (so the above VSTR and regex would
suggest to swap the order of the two words).

## Including spelling errors

To use the `divvun-cgspell` module, you need a spelling acceptor
(dictionary) FST and error model FST. These are the same format as the
files used by [hfst-ospell](https://github.com/hfst/hfst-ospell/). The speller isn't yet used to handle
real-word errors, just adding suggestions to unknowns.

The `divvun-cgspell` module should go before disambiguation in the
pipeline, so the disambiguator can pick the best suggestion in
context.

The module adds the tag `<spelled>` to any suggestions. The speller
module itself doesn't take any context into account, that's for later
steps to handle. As an example, you might have this unknown word as
input to the speller module:

"<coffe>"
            "coffe" ?

To which the output from the speller might be

"<coffes>"
            "coffes" ?
            "coffee" N Sg <W:37.3018> <WA:17.3018> <spelled> "<coffee>"
            "coffee" N Pl <W:37.3018> <WA:17.3018> <spelled> "<coffees>"
            "coffer" N Pl <W:39.1010> <WA:17.3018> <spelled> "<coffers>"
            "Coffey" N Prop <W:40.0000> <WA:18.1800> <spelled> "<Coffey>"

The *form* to be suggested is included as a "wordform-tag" at the very
end of each reading from the speller.

Now the later CG stages can use the context of this cohort to pick
more relevant suggestions (e.g. if the word to the left was "a", we
might want to `REMOVE` the plurals or even `SELECT` the singulars). We
could also `ADD/MAP` some relevant tags or relations.

Note that the readings added by the speller don't include any error
tags (tags with `&` in front). To turn these readings into error
underlines and actually show the suggestions, add a rule like

ADD (&typo SUGGESTWF) (<spelled>) ;

to the grammar checker CG (in practice we tend to only add the `&typo`
tag if none of the other grammar rules applied). The reason we add
`SUGGESTWF` and not `SUGGEST` is that we're using the wordform-tag
directly as the suggestion, and not sending each analysis through the
generator (as `SUGGEST` would do). See also the next section on how
replacements are built. So if, after disambiguation and grammarchecker
CG's, we had

"<coffes>"
            "coffee" N Pl <W:37.3018> <WA:17.3018> <spelled> "<coffees>"S &typo SUGGESTWF
            "coffer" N Pl <W:39.1010> <WA:17.3018> <spelled> "<coffers>"S &typo SUGGESTWF

then the final `divvun-suggest` step would simply use the contents of
the tags

"<coffers>"
    "<coffees>"

to create the suggestion-list, without bothering with generating from

"coffee" N Pl
    "coffer" N Pl

This makes the system more robust in case the speller lexicon differs
from the regular suggestion generator, and saves some duplicate work.

## How underlines and replacements are built

The `LEFT/RIGHT` relations (also `DELETE`) are used to expand the
underline of the error, to include several cohorts in one replacement
suggestion. We expand the underline until it matches the relation
targets that are furthest away, so if you have several such relation
targets to the left of the central cohort, the underline expands to
the leftmost one.

A matching `co&errtag` isn't strictly needed on the non-central word,
but is recommended in case we can have several error types and need to
keep replacements separate (to avoid silly combinations of
suggestions).

Another use for the `co&errtag` is to have a way to relate corrected
`SUGGEST` readings within complex errors, without the correct reading
being matched by sets which look for error tags. For example, say that
you have a `LIST Errors = &missing &typo …;` and a rule which looks
for an error-tagged pronoun to the left `(-1 Pron + Errors)`. Now
earlier in the grammar checker rules you may have added a new
suggestion cohort with a reading `Pron SUGGEST` – if you gave that
reading the tag `&missing` to relate it to the central word, the
context `(-1 Pron + Errors)` would match, which is probably not what
you want. But if you instead give the suggestion the tag `co&missing`,
then you can rely on tags like `&missing` being only on actual
mistakes in the input.

When we have a `DELETE` relation from a reading with an `&errtag` and
there are be multiple source-cohort error tags, the deletion target
needs to have a `co&errtag`, so that we only delete in the replacement
for `&errtag` (not from the replacements for `&other-errtag`). See the
section on [Alternative suggestions for complex errors altering
different parts of the error](#orge26043f) for more info on this.

By default, *a cohort's word form is used to construct the
replacement*. So if we have the sentence "we was" where "was" is
**central** and tagged `&typo`, and there's a `LEFT` relation to "we",
then the default replacement if there were no `SUGGEST` tags would
simply be the input "we was" (which would be filtered out since it's
equal, giving no suggestions).

If we now add a `SUGGEST` reading on "we" that generates "he" then we
get a "he was" suggestion. `SUGGEST` readings with matching
(co-)error tags are prioritised over input word form.

If we also have a `SUGGEST` for was→are for the possible replacment
"we are" (tagged `&agr`) – now we don't want both of these to apply at
the same time giving *"we is". In this case, we need to ensure we have
disambiguating `co&errtype` tags on the `SUGGEST` readings. The
following CG parse:

"<we>"
        "we" Prn &agr                 ID:1 R:RIGHT:2
        "he" Prn SUGGEST co&agr-typo ID:1 R:RIGHT:2
    : 
    "<was>"
        "be" V 3Sg &agr-typo       ID:2 R:LEFT:1
        "be" V 3Pl co&agr SUGGEST ID:2 R:LEFT:1

will give us all and only the suggestions we want ("he was" and "we
were", but not *"he were").

## Summary of special tags and relations

CG lets you define all kinds of new tags and relation-names and within
CG you are free to make your own conventions as to what they mean.
However, in the Divvun grammar checker system, certain CG tags and
relation-names have special meanings to the rest of the system. Below
is a summary of the special tags/relations and their uses. In
addition, note that all divvun error tags need to start with the `&`
character, but apart from that are free to name errors as long as they
don't conflict with the below special tags.

### Tags

-   `SUGGEST` on a reading means that `divvun-suggest` should try to
    generate this reading into a form for suggestions, using the
    generator FST. See [Simple grammarchecker.cg3 rules](#org0955ce1).
-   `SUGGESTWF` on a reading means that `divvun-suggest` should use the
    reading's wordform-tag (e.g. a tag like
    
        "<Cupertino>"S
    
    on a *reading*, not as the first line of a cohort) as a suggestion.
    See [Including spelling errors](#org26182db).
-   `<spelled>` is added by `divvun-cgspell` to any suggestions it
    makes. See [Including spelling errors](#org26182db).
-   `co&` is a tag prefix – `co&` is often used to mark a reading as a
    non-central part of the underline of `&errtag`, see [Deleting
    words](#org4d2c8ef) and related sections. (You may also see
    `COERROR &errtag` in older rules; this was the
    old way of writing `co&errtag`.) We also often add `co&` error
    tags to `SUGGEST` readings in order to relate a suggestion to a
    complex error without that (correct) reading being matched by sets
    which match error readings. See 
    [How underlines and replacements are built](#orgb25740d) for details.
    Another reason to use `co&` is to ensure we can refer to the
    central error with `$1` in `errors.source.xml`.
-   `DROP-PRE-BLANK` means the suggestion should trim the preceding
    space (useful for fixing spaces before punctuation).
-   `ADDED` means this cohort was added (typically with `ADDCOHORT`)
    and should be a part of the suggestion for the error. It will appear
    after the blank of the preceding cohort, and will not be the central
    cohort of the error. See [Adding words](#orgb76a5c9).
-   `ADDED-BEFORE-BLANK` is like `ADDED`, except that it appears
    before the blank of the preceding cohort.
-   Any other tag starting with `&` is an error type tag,
    e.g. `&real-hallan` or `&punct-rihkku`, defined by the CG rule
    author. It should also appear in `errors.xml` (without the initial
    `&`) with a human-readable error message.

### Relations

-   `LEFT` and `RIGHT` are used to extend the underline to added
    cohorts; see [Adding words](#orgb76a5c9) and
    [Adding literal word forms, altering existing wordforms](#orge23663a).
    `LEFT` if the added word is to the left of the error tag, `RIGHT` if the added word is to the right of the error tag.
-   `DELETE1`, `DELETE2` etc. (but not just `DELETE` without a number) are used to say that a word in the
    context of this error should be deleted in the suggestion. See [Deleting words](#org4d2c8ef).
-   `$2` (and `$3` etc.) are used to make wordforms in the context
    available to human-readable error messages in `errors.xml`. Note
    that `$1` is always the wordform of the *central* cohort of the
    error (so don't add `$1` as a relation). See [Simple grammarchecker.cg3 rules](#org0955ce1).

# Troubleshooting

If you get

terminate called after throwing an instance of 'std::regex_error'
      what():  regex_error

then your C++ compiler is too old. See [Prerequisites](#org6558baf).

If you get

configure: error: 'g++  -std=c++17 -Wall -I/usr/include/hfst/ @GLIB_CFLAGS@  -I/usr/include/ ' does not accept ISO C++17

then you may be at the receiving end of
<https://github.com/hfst/hfst/issues/366>. A workaround is to edit
`/usr/lib64/pkgconfig/hfst.pc` and simply delete the string
`@GLIB_CFLAGS@`.

# References / more documentation

The architecture of systems using libdivvun is described in

-   Wiechetek, L., Moshagen, S., & Unhammer, K. B. (2019, February).
    [Seeing more than whitespace—Tokenisation and disambiguation in a North Sámi grammar checker](https://aclanthology.org/W19-6007.pdf). In
    *Proceedings of the 3rd Workshop on the Use of Computational Methods in the Study of Endangered Languages Volume 1 (Papers)*
    (pp. 46-55).

libdivvun

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