GraSs: A Taxonomy of Grammar Smells

Organisation
global problems

Navigation
problems with navigating through the grammar

Structure
harmful relationships among grammar components

Convention
violations of visual policies

Notation
metalanguage-related

Parsing
parsing techniques related smells

Duplication
the same fragment is repeated

Echo
same rule occurs twice or more

Clone
same right hand side occurs twice or more

Foldable
nonterminal's right hand side is not unique

Common
common subexpressions

Permuted
permutations in commutative combinators

Lookalike
near-clones

Clone Edit!

Related smells: Duplicate Code, Reinvent the Wheel, Cut and Paste Programming, Unfactored Hierarchy, Duplicate Entity

Nonterminals that have exactly the same definitions, are only cluttering the grammar, and can be painlessly united. In clone management research, these are called “type 1 clones”, we will revisit this classification later when defining Lookalike.

The GraSs taxonomy is a joint effort maintained by Dr. Vadim Zaytsev a.k.a. @grammarware. Page last updated in March 2021.