# Let's Build A Simple Interpreter. Part 8.

DevFeed: [Let's Build A Simple Interpreter. Part 8.](<https://devfeed.tech/articles/let-s-build-a-simple-interpreter-part-8-33329.md>)

Original publisher: [Read original article](<https://ruslanspivak.com/lsbasi-part8/>)

Author: Ruslan Spivak

Published: 2016-01-18T11:10:00Z

Content type: tutorial

Language: en

Sources: [Ruslan Spivak](<https://devfeed.tech/sources/ruslan-spivak.md>)

Topics: [Parsing](<https://devfeed.tech/topics/parsing.md>), [Parser](<https://devfeed.tech/topics/parser.md>)

Tags: [blog](<https://devfeed.tech/tags/blog.md>), [constructor](<https://devfeed.tech/tags/constructor.md>), [expression](<https://devfeed.tech/tags/expression.md>), [extend](<https://devfeed.tech/tags/extend.md>), [generate](<https://devfeed.tech/tags/generate.md>), [here](<https://devfeed.tech/tags/here.md>), [node](<https://devfeed.tech/tags/node.md>), [rules](<https://devfeed.tech/tags/rules.md>)

## AI overview

This tutorial explains how to add unary plus and unary minus operators to an interpreter. It covers grammar changes, a UnaryOp abstract syntax tree node, and parser and interpreter updates.

## Source excerpt

Today we'll talk about unary operators, namely unary plus (+) and unary minus (-) operators. A lot of today's material is based on the material from the previous article, so if you need a refresher just head back to Part 7 and go over it again. Remember: repetition is the ...