GraSs: A Taxonomy of Grammar Smells

Organisation
global problems

Navigation
problems with navigating through the grammar

Structure
harmful relationships among grammar components

Proxy
indirect uses

Dependency
antipatterns in use

Complexity
metric-based smells

Chain
right hand side is a nonterminal

Throwaway
a nonterminal used only once

Weak
a nonterminal does not form a proper abstraction

Ghost
a subexpression that should have been a nonterminal

Multitool
a nonterminal that represents two or more concepts

Ghost Edit!

Related smells: Missing Encapsulation

If an expression, especially a Common subexpression, could have formed a proper abstraction, but is not made into a separate nonterminal, we speak of it as a Ghost.

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