Snowball is a small string processing language for creating stemming algorithms for use in Information Retrieval, plus a collection of stemming algorithms implemented using it.

Snowball was originally designed and built by Martin Porter. Martin retired from development in 2014 and Snowball is now maintained as a community project. Martin originally chose the name Snowball as a tribute to SNOBOL, the excellent string handling language from the 1960s. It now also serves as a metaphor for how the project grows by gathering contributions over time.

The Snowball compiler translates a Snowball program into source code in another language - currently Ada, ISO C, C#, Go, Java, Javascript, Object Pascal, Python and Rust are supported.

This repository contains the source code for the snowball compiler and the stemming algorithms. The snowball compiler is written in ISO C - you'll need a C compiler which support C99 to build it (but the C code it generates should work with any ISO C compiler).

See https://snowballstem.org/ for more information about Snowball.

What is Stemming?

Stemming maps different forms of the same word to a common "stem" - for example, the English stemmer maps connection, connections, connective, connected, and connecting to connect. So a search for connected would also find documents which only have the other forms.

This stem form is often a word itself, but this is not always the case as this is not a requirement for text search systems, which are the intended field of use. We also aim to conflate words with the same meaning, rather than all words with a common linguistic root (so awe and awful don't have the same stem), and over-stemming is more problematic than under-stemming so we tend not to stem in cases that are hard to resolve. If you want to always reduce words to a root form and/or get a root form which is itself a word then Snowball's stemming algorithms likely aren't the right answer.

Building Snowball

GNU make is required to build Snowball.

The build system is currently structured as two separate stages for many of the target languages.

The first stage builds the Snowball compiler and runs it to create target language code (and it can also run tests on each stemmer). The expectation is that you then create a "distribution" tarballs of this code with make dist (or to create one for a specific target language, e.g. make dist_libstemmer_c for C). These tarballs are created in the dist/ subdirectory.

To actually build the libstemmer library you then unpack and build the distribution tarball, e.g. for C:

tar xf dist/libstemmer_c-2.2.0.tar.gz
cd libstemmer_c-2.2.0
make

Cross-compiling

If cross-compiling starting from the git repo, the Snowball compiler needs to be built with a native compiler then libstemmer with the cross-compiler. For example:

make CC=cc dist_libstemmer_c
tar xf dist/libstemmer_c-2.2.0.tar.gz
cd libstemmer_c-2.2.0
make CC=riscv64-unknown-linux-gnu-gcc

If you are cross-compiling to or from Microsoft Windows, you'll need to also work around an assumption in libstemmer's Makefile which sets EXEEXT based on the OS you are building on:

ifeq ($(OS),Windows_NT)
EXEEXT=.exe
endif

For example, if cross-compiling from Linux to Microsoft Windows, use something like this for the libstemmer build:

make CC=x86_64-w64-mingw32-gcc EXEEXT=.exe

When going the other way, you'll need to use EXEEXT=.