BNFC

A compiler front-end generator.

https://bnfc.digitalgrammars.com/

LTS Haskell 24.18:	2.9.6.1
Stackage Nightly 2025-11-04:	2.9.6.1
Latest on Hackage:	2.9.6.1

See all snapshots BNFC appears in

BSD-3-Clause licensed

Maintained by [email protected]

This version can be pinned in stack with:BNFC-2.9.6.1@sha256:0d0f34c6c88877f9abfac8b84f5687e61e4878e426d249a64aa6d2f4c436dce5,9522

Module documentation for 2.9.6.1

BNFC

Depends on 13 packages(full list with versions):

array, base, BNFC, containers, deepseq, directory, filepath, mtl, pretty, process, string-qq, time, transformers

Used by 1 package in nightly-2025-11-04(full list with versions):

BNFC

The BNF Converter

What is the BNF Converter?

The BNF Converter (bnfc) is a compiler construction tool generating a compiler front-end from a Labelled BNF (LBNF) grammar. It is currently able to generate Haskell, Agda, C, C++, Java, and OCaml, as well as XML representations.

Given a LBNF grammar the tool produces:

an abstract syntax implementation
a case skeleton for the abstract syntax in the same language
an Alex, Ocamllex, JLex, or Flex lexer generator file
a Happy, Ocamlyacc, Menhir, ANTLR, CUP, or Bison parser generator file
a pretty-printer as a Haskell/Agda/C/C++/Java/Ocaml module
a Latex file containing a readable specification of the language

More information: http://bnfc.digitalgrammars.com/

Installation

Some binaries are available at https://github.com/BNFC/bnfc/releases. Installation from the Haskell sources is possible via stack or cabal.

Installation via stack (recommended)

You need a running installation of stack. To install and run the latest version of bnfc from stackage, enter at the command line:

  stack install BNFC
  bnfc --help

BNFC versions in major Stackage LTS snapshots:

GHC	LTS	BNFC
8.8.4	16.31	2.8.4
8.10.7	18.28	2.9.4
9.0.2	19.33	2.9.4
9.2.8	20.26	2.9.4.1
9.4.8	21.25	2.9.5
9.6.7	22.44	2.9.5
9.8.4	23.27	2.9.5
9.10.2	24.3	2.9.5

Installation via cabal

You need a running installation of a recent version of GHC and Cabal, most easily available via the GHCup. To install bnfc from hackage, enter at the command line:

  cabal install BNFC
  bnfc --help

Installing the development version

To install the development version of bnfc with the latest bugfixes (and regressions ;-)):

  git clone https://github.com/BNFC/bnfc.git
  cd bnfc/source

and then either

  cabal install

  stack install --stack-yaml stack-9.12.yaml

(replace 9.12 with your GHC major version, and if you want to build with your installed GHC then add flag --system-ghc).

Mini tutorial

Build a first parser in 5 min (Haskell backend):
1. In a fresh directory, prepare a grammar file Sum.cf with the following content:
```
EInt.  Exp ::= Integer;
EPlus. Exp ::= Exp "+" Integer;
```
2. Build a parser (in Haskell) with bnfc:
```
bnfc -d -m Sum.cf  &&  make
```
  The make step needs the Haskell compiler GHC, the lexer generator alex and the parser generator happy (all included in the GHC installation).
3. Inspect the generated files in directory Sum.
4. Test the parser.
```
echo "1 + 2 + 3" | Sum/Test
```

Try the C-family backends. (The prerequisites, GNU C(++) compiler (gcc / g++), lexer generator flex and parser generator bison, are usually present):

bnfc --c   -m -o sum-c   Sum.cf  &&  make -C sum-c    &&  echo "1 + 2 + 3" | sum-c/TestSum
bnfc --cpp -m -o sum-cpp Sum.cf  &&  make -C sum-cpp  &&  echo "1 + 2 + 3" | sum-cpp/TestSum

Try the other backends:

Option	Backend
`--java`	Requires Java, JLex or JFlex, and CUP.
`--java-antlr`	Requires ANTLR.
`--ocaml`	Requires OCaml, `ocamllex` and `ocamlyacc`.
`--ocaml-menhir`	Uses menhir instead of `ocamlyacc`.
`--agda`	Produces Agda bindings to the parser generated for Haskell.
`--pygments`	Produces a lexer definition for the Python highlighting suite Pygments.

Documentation

https://bnfc.readthedocs.org/en/latest/

Support

You can discuss with us issues around bnfc on our mailing list [email protected].

For current limitations of bnfc, or to report a new bug, please consult our issue tracker.

Contribute

Issue Tracker: https://github.com/BNFC/bnfc/issues
Source Code: https://github.com/BNFC/bnfc
Haskell coding style guide: https://github.com/andreasabel/haskell-style-guide/
Some pull request etiquette:
- Document, document, document! (See style guide)
- Include test cases that cover your feature.
- Include changelog entry.
- More etiquette: E.g. https://gist.github.com/mikepea/863f63d6e37281e329f8

License

The project is licensed under the BSD 3-clause license.

BNFC versions until 2.8.4 released under the GNU General Public License.

Example uses of the BNF Converter

In research:

NASA’s OGMA tool uses LBNF for its grammars, e.g. for a subset of C 99.

In teaching:

Course Programming Language Technology at Chalmers / Gothenburg University.

Changes

Unreleased

2.9.6.1

Andreas Abel [email protected], August 2025

Haskell: restore LANGUAGE DeriveDataTypeable in generated Abs.hs; fixes regression in 2.9.6 [#507]

Builds with GHC versions:

with cabal, GHC 8.0 - 9.12
with stack, GHC 8.4 - 9.12

2.9.6

Andreas Abel [email protected], August 2025

C: preserve case in constructors (union): e.g. label EInt now is union member eInt_ rather than eint_ [#479]
Haskell: lex ASCII 222 as upper rather than lower case letter [#497]
Haskell: no longer derive Typeable (obsolete since GHC 7.10) [#503]
Haskell: drop support for GHC 7, generated code needs at least GHC 8.0

Builds with GHC versions:

with cabal, GHC 8.0 - 9.12
with stack, GHC 8.4 - 9.12

2.9.5

Andreas Abel [email protected], July 2023

C/C++/Java: escape newline etc. when printing String and Char literals [#449]
Java/ANTLR: unescape String and Char literals in parser (needs Java ≥ 15) [#451]
Java/ANTLR: fix case problem with language names like C [#455]
Java with line numbers: compatibility with jflex ≥ 1.8 [#453]
Haskell/GADT: generated ComposOp.hs no longer needs mtl library [#438]
Ocaml: fixed a crash in printer with unbalanced } [#439]
Ocaml: lex escape sequences in Char [#452]
Ocaml: removed superfluous let rec in the printers for token categories

Tested GHC versions:

with cabal, GHC 7.10 - 9.6
with stack, GHC 8.2 - 9.6

2.9.4.1

Andreas Abel [email protected], December 2022

C/C++: allow space characters in token definitions again [#431] (regression in 2.9.0)
installation: get rid of cabal-doctest dependency [#429]

Tested GHC versions:

with cabal, GHC 7.10 - 9.4
with stack, GHC 8.2 - 9.4

2.9.4

Andreas Abel [email protected], February 2022

LBNF: empty token types are now forbidden [#388]
Agda: support position information via --functor [#405]
C/C++: use size_t and -Wsign-conversion [#391]
C++: repair broken --line-numbers [#390], regression in 2.9.2 by [#349]
Haskell: fix a problem with layout stop words and top-level layout [#399,#413]
Haskell: generated test parser can parse several files now [#400]
Java: use L.valueOf() instead of deprecated new L() for literal classes L [#402]
Ocaml: non-terminals in generated parser are now type-annotated [#407]
Ocaml: sanitize bound variables in define
Ocaml/Menhir: update parse error mechanism to Menhir 2021/12/30 [#414]

Contributors:

Michał Radwański [#390,#391]
Beatrice Vergani [#399,#400]

2.9.3

Andreas Abel [email protected], September 2021

BNFC now uniformly signs generated files with its version number [#373]
C/C++: include stdio.h in parser header files [#381]
C++: fixed parser regression in 2.9.2: missing #include <algorithm> [#377]
Ocaml: lex CR as whitespace [see also #376]
Ocaml: correct position in parse errors [#380]
Ocaml/Haskell: make printer for lists categories total [#383]

2.9.2

Andreas Abel [email protected], June 2021

Major improvements

Haskell: layout keywords can now be stacked on the same line [#354], see https://bnfc.readthedocs.io/en/latest/lbnf.html#stacking-layout-keywords
C: new methods free_* and clone_* to deallocate and clone syntax trees [#348]
C/C++ backends now create reentrant parsers [#349]

Bug fixes and small improvements

Haskell-GADT: generated code is warning free [#346]
Haskell: fixes in layout preprocessor [#343,#344,#345,#352,#353]
Haskell: print [Char] correctly, removed method prtList [#359]
Haskell: added missing import [#368], regression introduced in 2.9.1 by [#331]
C: fixed a space leak when parsing from a string in memory [#347]
C: removed errorneous defined constructors from Skeleton.c
C++: defined constructors now reside in Absyn [#287]
Java: defined constructor now reside in AbsynDef.java [#287]
Ocaml: fixed translation of nested defined constructors
C/C++/Java: Pre/post/mixfix lists are now printed correctly [#358]
all: defined constructors involving list expressions work now [#363]
all: printers render braces on their own line [#366]

Cosmetical changes

C/C++: instead of _SYMB_nnn, more readable token names in lexer & parser

2.9.1

Andreas Abel [email protected], March 2021

Main new feature

Haskell: the --functor option now produces position-annotated ASTs [#176,#327]. Thanks @Commelina!

Bug fixes and small improvements

Haskell: fix generated Makefile and test parser for --glr mode [#340]
Haskell(/GADT): generated modules import Prelude explicitly, compatible with {-# LANGUAGE NoImplicitPrelude #-}
Haskell: generated code is warning free [#331]
Haskell: generated printer more robust wrt. identifier clashes [#337]
Haskell/C: handle token constructors in define expressions [#338]
Java/ANTLR: removed more superfluous quotation in lexer character sets [#329]
Ocaml: fix syntax error in generated printer [#330]
LBNF: more sanity checks [#339]
Tested with GHC 9.0

2.9.0

Andreas Abel [email protected], December 2020

Major changes

New license: BSD 3-clause [#308]
LBNF: removed delimiters pragma [#308]
Haskell: removed options --alex1, --alex2, --sharestrings, --profile, and --cnf [#265]
C#: backend removed [#265]

Bug fixes

LBNF: allow list categories in entrypoints pragma [#306]
LBNF: report clashes between token and ordinary categories [#323]
C: strdup is not part of C89 standard, _POSIX_C_SOURCE required [#318]
C/C++: fixed buffer overrun in String literal lexer [#316]
C++: fixed regressions (one of them #310) introduced by #288
C/C++/OCaml: allow unicode characters in token definitions [#324]
C/OCaml: sanitize grammar file names [#325]
Java/ANTLR: removed superfluous quotation in lexer character sets [#319]

2.8.4

Andreas Abel [email protected], October 2020

GHC versions 7.10 - 8.10 supported, dropped GHC 7.6 and 7.8
LBNF: whitespace list separators are now accepted; treated like “” [#70]
define pragma now implemented by all maintained backends [#266, #285]
BNFC performs more sanity checks on the grammar, reports errors with source locations [#186, #213, #214]
option --check to only perform sanity checks [#286]
Backends now more resilient against keyword and name clashes (e.g. via qualified imports) [#278, #289]
Haskell: new option --text-token to use Data.Text instead of String in the lexer [#167]
Haskell: allow block comment delimiters of any length [#169, #202]
Haskell: define Err monad as Either String [#273], migration guide at https://bnfc.readthedocs.io/en/v2.8.4/user_guide.html#haskell-backend
Haskell: IsString instances for Ident-like token types [#192]
C/C++/Java: support multiple block comment forms per grammar [#202]
C++(STL): parser now throws exception on parse error [#288]
C++: fixed quadratic behavior in C++-generated printer (regression in 2.8.2)
Java: escape JFlex special characters [#299]
Java/ANTLR: emit start rules to work around ANTLR issue #2689 [#272]
Ocaml: new flag --menhir to generate parser with menhir instead of ocamlyacc
Bug fixes: #163, #169, #196, #212, #235, #256, #264, #269, #274, #276, #277, #279, #282, #283, #290
Fact-checking and revising LBNF documentation at https://bnfc.readthedocs.io/en/v2.8.4/lbnf.html

2.8.3

Andreas Abel [email protected], August 2019

GHC 8.8 compatibility
Stack installation supported by provided .yaml files [#198]
Unicode support in lexer, excl. C, C++ and Ocaml [#249]
LBNF: support \r (carriage return) and \f (form feed) in token declaration [#257]
LBNF: allow numbered categories (like Foo2) independent of coercions [#210]
Agda: new (experimental) backend, providing bindings to AST/parser/printer of Haskell backend
C: supports now the -l option to give error locations [#238]
C: correct function names in generated skeletons [#239]
C, C++: handle regular expression difference (subtraction) correctly [#237]
Haskell: generates now more fine-grained Makefile that invokes bnfc on changed .cf file
Haskell: use qualified import of AST in generated printer [#128,#228]
Haskell: printer code no longer produces deprecation warning concerning OverlappingInstances [#233]
Haskell/CNF: fixed problem with Any type in generated code [#216]
Haskell/CNF: generated test program now same name (Test) as w/o –cnf
Haskell/GLR: correct module header in .y file [#252]

2.8.2

Andreas Abel [email protected], November 2018

GHC 8.4 compatibility [#227,#236]
bnfc now puts current timestamp on all created files, even unchanged ones [#219]
bnfc is now more accepting about border-line terminals [#149]
Improved error messages [#144] in particular on undefined categories [#151]
C: Emit correct function prototypes [#185]
C++: Fix buffer overrun in pretty printer [#242]
C++: Fix regression introduced in 2.8 in Skeleton.H [#164]
C++: Replace %name-prefix with %define api.prefix in bison files [#181]
C++: Fix a bug that appeared if you had a category named “List”
C, C++: Add usage output to the test program [#141]
C, C++: Fix a bug in the parser file when using -p [#172]
C, C++, OCaml, Java: Accept ’ or “ as comment delimiters [#146]
Haskell: Generated code mostly hlint-warning free
Haskell: Small fixes [#166,#170,#222]
Java: Add an experimental ANTLR4 backend [#155]
Java: Add support for passing line numbers to parser [#217,#224,#226]
OCaml: Reserved symbols now have a higher precedence than predefined tokens as in Haskell
Some updates of the documentation [#211,#223]
And various small fixes [#139,#159,#195,#201,#215]

2.8.1

Grégoire Détrez [email protected], February 2016

Fix compatibility with GHC 7.10.2 and Alex 3.14
Fixed #160

2.8

Grégoire Détrez [email protected], May 2015

Builds with ghc 7.10.1
Add support for JFlex (java)
Add an option to generate files in an other directory
Add an experimental option that turns the AST into a parametrized functor (in Haskell only)
New pygment backend to generate syntax highlighters
Bug fixes

2.7.1

Grégoire Détrez [email protected], October 2014

Generated haskell code is now warning free
Removed unused terminal in happy
Correctly escape backslashes in symbols
Fix problem that was preventing custom tokens to work in OCaml if they conflict with the build-in Ident
BNFC build is also warning free (ghc 7.4.2)
Test programs return non-zerro exit code on parse error

2.7.0.0

Grégoire Détrez [email protected], September 2014

Add token support for Ocaml
New option parser
Adds an optional argument to change Makefile name
Add a –ghc option to derive Data, Typeable, Generic in Haskell
New online documentation (https://bnfc.readthedocs.org)
Derive Read for newtype decls in Haskell
New option to get the version number –version
Remove the F# backend
Remove the Java4 backend
New Applicative and Alternative instances to Err
Remove the coupling between building the parser and the pdf from latex
Improvement to the CNF Backend
Bug fixes #92, #21, #34, #33, #90, #30, #60

2.5.0

Grégoire Détrez, April 2013

2.6.0.3

Grégoire Détrez, January 2013

2.4.2.1

Andreas Abel [email protected], July 2012

2.4.2.0

Thomas Hallgren, September 2010

2.4.1.1

Markus Forsberg, September 2010