# Ruslan Spivak Ruslan's Blog This is one page of public article previews, not the complete archive. Follow Next page to continue. Summaries are not the original full articles. ## 5 to 18: Why Your Count Might Be Off by One DevFeed: [5 to 18: Why Your Count Might Be Off by One]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2025-08-19T15:37:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Code](), [coding](), [bug]() Tags: [blog](), [bug](), [code](), [numbers](), [range]() ### AI overview A tutorial explains how to count integers in an inclusive range using b - a + 1. It uses the range from 5 to 18 to show why subtracting the endpoints alone produces an off-by-one error, then connects the mistake to dates, strings, workout plans, floors, and loop boundaries in code. ### Source excerpt Quick question: How many numbers are there from 5 to 18, including both ends? Your first instinct might be to subtract: 18 - 5 = 13 Feels right. But it's wrong. It's a small thing, and kind of basic, but this mistake got me more times than I'd like ... ## Book Notes: The Dark Art of Linear Algebra by Seth Braver -- Chapter 1 Review DevFeed: [Book Notes: The Dark Art of Linear Algebra by Seth Braver -- Chapter 1 Review]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2025-07-15T14:38:00Z Content type: opinion Language: en Sources: [Ruslan Spivak]() Topics: [Mathematics](), [math]() Tags: [addition](), [arrow](), [blog](), [book](), [mathematics](), [review](), [vector]() ### AI overview A review of Chapter 1 of Seth Braver's The Dark Art of Linear Algebra, focusing on geometric interpretations of vectors, vector addition, subtraction by addition, and the roles of commutativity and associativity. ### Source excerpt "Mathematics is the art of reducing any problem to linear algebra." -- William Stein If you've ever looked at a vector and thought, "Just a column of numbers, right?", this chapter will change that. The Dark Art of Linear Algebra (aka DALA) by Seth Braver opens with one of the ... ## Book Notes: Full Frontal Calculus by Seth Braver -- Chapter 1 Review DevFeed: [Book Notes: Full Frontal Calculus by Seth Braver -- Chapter 1 Review]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2025-06-20T14:07:00Z Content type: opinion Language: en Sources: [Ruslan Spivak]() Topics: [math](), [Learning](), [Machine Learning & Artificial Intelligence]() Tags: [blog](), [book](), [math](), [review]() ### AI overview A review of Chapter 1 of Seth Braver's Full Frontal Calculus, focusing on infinitesimals, derivatives, Leibniz's dy/dx notation, and introductory differentiation rules. The reviewer found the book intuitive and useful for rebuilding math foundations for AI and machine learning. ### Source excerpt "Where there is life, there is change; where there is change, there is calculus." -- Seth Braver I recently went back to studying math to rebuild my foundations for AI and machine learning. I didn't expect to enjoy a calculus book this much. Shocking, I know. But that's exactly ... ## 7 Things That Helped Me Grow as a Software Engineer DevFeed: [7 Things That Helped Me Grow as a Software Engineer]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2024-08-09T16:26:00Z Content type: opinion Language: en Sources: [Ruslan Spivak]() Topics: [Learning](), [Software](), [coding](), [ci]() Tags: [advice](), [blog](), [growth](), [learning](), [reviews](), [skills](), [software-engineer]() ### AI overview A personal reflection on principles that helped the author grow as a software engineer, including drive, delivering results, choosing impactful projects, developing deep expertise, teaching, and handling criticism. ### Source excerpt Hi everyone, Growth as a software engineer is an ongoing journey. Looking back, a few key principles helped me progress during the early days of my career. These lessons shaped my path, and many of them continue to guide me today, even though I'm no longer an individual contributor ... ## Fundamental Skills for Software Engineers DevFeed: [Fundamental Skills for Software Engineers]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2024-07-31T17:04:00Z Content type: article Language: en Sources: [Ruslan Spivak]() Topics: [Software Engineering](), [coding](), [Data structures](), [Algorithms](), [Architecture & Design](), [Databases](), [distributed-systems](), [math]() Tags: [algorithms](), [architecture](), [blog](), [data-structures](), [databases](), [distributed-systems](), [fundamentals](), [math](), [programming](), [software]() ### AI overview The article argues that software engineers should build durable fundamentals because technologies and frameworks change quickly. It recommends focusing on programming languages, software design and architecture, data structures and algorithms, operating systems, networking, databases, distributed systems, mathematics, and soft skills. ### Source excerpt "Fundamentals are the foundation of excellence. Without a strong base, you cannot reach your full potential." - John Wooden Hey there! Let's talk fundamentals today. Why are they important? John Wooden's quote sums it up nicely, but let's unpack it a bit more: Strong foundation: A solid grasp ... ## Let's Build A Simple Interpreter. Part 19: Nested Procedure Calls DevFeed: [Let's Build A Simple Interpreter. Part 19: Nested Procedure Calls]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2020-03-19T12:45:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Code](), [file]() Tags: [blog](), [code](), [github](), [parameter](), [program](), [scope](), [scopes](), [variable](), [variables]() ### AI overview This tutorial explains how to execute nested procedure calls in a simple interpreter. It demonstrates nested procedures Alpha and Beta, examines their activation records, and fixes the nesting level for Beta by using the scope level stored in the scoped symbol table. ### Source excerpt What I cannot create, I do not understand. --- Richard Feynman ## EOF is not a character DevFeed: [EOF is not a character]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2020-03-01T16:53:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [C](), [IO](), [Unix](), [ASCII](), [Streams](), [Code]() Tags: [ascii](), [blog](), [c](), [code](), [computer](), [example](), [file](), [function](), [library](), [linux](), [mac-os](), [python](), [standard-library](), [stream](), [systems](), [text](), [unix](), [value]() ### AI overview This tutorial explains that EOF in C is not a character and is not stored at the end of a file. It examines EOF in Unix I/O, its usual value of -1, and why that value cannot represent a character. ### Source excerpt I was reading Computer Systems: A Programmer's Perspective the other day and in the chapter on Unix I/O the authors mention that there is no explicit "EOF character" at the end of a file. ## Let's Build A Simple Interpreter. Part 18: Executing Procedure Calls DevFeed: [Let's Build A Simple Interpreter. Part 18: Executing Procedure Calls]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2020-02-20T13:00:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Code](), [function](), [Algorithm]() Tags: [algorithm](), [blog](), [code](), [constructor](), [create](), [function](), [local-variables](), [object](), [parameter](), [program](), [variables]() ### AI overview This tutorial extends an interpreter to execute procedure calls. It focuses on procedures that access parameters and local variables, explaining activation records, call-stack handling, procedure execution, and the implementation of the visit_ProcedureCall method. ### Source excerpt Do the best you can until you know better. Then when you know better, do better. ― Maya Angelou ## Let's Build A Simple Interpreter. Part 17: Call Stack and Activation Records DevFeed: [Let's Build A Simple Interpreter. Part 17: Call Stack and Activation Records]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2019-08-28T15:00:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [function](), [data](), [Hardware]() Tags: [blog](), [build](), [function](), [hardware](), [implement](), [memory](), [series](), [simple](), [values](), [variable]() ### AI overview Part 17 of a series on building an interpreter explains plans to implement a new memory system for programs, procedure calls, and function calls, replacing the GLOBAL_MEMORY dictionary. It introduces memory as a way to store and access data and distinguishes physical memory from interpreter-level storage by variable names. ### Source excerpt You may have to fight a battle more than once to win it. - Margaret Thatcher ## Let's Build A Simple Interpreter. Part 16: Recognizing Procedure Calls DevFeed: [Let's Build A Simple Interpreter. Part 16: Recognizing Procedure Calls]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2019-07-23T12:20:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Parser](), [Parsing](), [Code]() Tags: [blog](), [components](), [examples](), [how-to](), [semantic](), [syntax](), [token]() ### AI overview This tutorial extends a simple interpreter to recognize procedure calls. It explains the required parser, grammar, and AST changes so procedure-call programs can be parsed and traversed by the semantic analyzer and interpreter without errors. ### Source excerpt Learning is like rowing upstream: not to advance is to drop back. -- Chinese proverb ## Improving Error Reporting in a Simple Interpreter DevFeed: [Improving Error Reporting in a Simple Interpreter]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2019-06-21T09:45:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [error reporting](), [Python](), [Exception](), [Parsing]() Tags: [blog](), [custom-exceptions](), [error-reporting](), [parsing](), [python]() ### AI overview This tutorial improves error reporting in a simple interpreter's lexer, parser, and semantic analyzer. It adds error codes, custom exceptions, token position tracking, a scope command-line option, and Python 3.7+ support. ### Source excerpt "I am a slow walker, but I never walk back." -- Abraham Lincoln And we're back to our regularly scheduled programming! :) Before moving on to topics of recognizing and interpreting procedure calls, let's make some changes to improve our error reporting a bit. Up until now, if there was ... ## Let's Build A Simple Interpreter. Part 14: Nested Scopes and a Source-to-Source Compiler. DevFeed: [Let's Build A Simple Interpreter. Part 14: Nested Scopes and a Source-to-Source Compiler.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2017-05-08T09:45:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Compiler](), [Programming](), [Parser]() Tags: [blog](), [code](), [compiler](), [deep-dive](), [programming-language](), [scopes](), [source]() ### AI overview A tutorial on nested scopes in interpreters. It explains scoped symbol tables, name resolution, procedure declarations with formal parameters, semantic checks, scope trees, and a source-to-source compiler. ### Source excerpt Only dead fish go with the flow. As I promised in the last article, today we're finally going to do a deep dive into the topic of scopes. This is what we're going to learn today: We're going to learn about scopes, why they are useful, and ... ## Let's Build A Simple Interpreter. Part 13: Semantic Analysis. DevFeed: [Let's Build A Simple Interpreter. Part 13: Semantic Analysis.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2017-04-27T05:00:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [syntax](), [Parsing](), [Parser](), [compilers](), [context]() Tags: [blog](), [compilers](), [errors](), [parsing](), [separate](), [syntax](), [types]() ### AI overview This tutorial explains semantic analysis in interpreters and compilers. It shows why grammatically correct Pascal programs can still contain errors, and how an abstract syntax tree, symbol table, and separate semantic-analysis phase can detect issues such as using undeclared variables. ### Source excerpt Anything worth doing is worth overdoing. Before doing a deep dive into the topic of scopes, I'd like to make a "quick" detour and talk in more detail about symbols, symbol tables, and semantic analysis. In the spirit of "Anything worth doing is worth overdoing", I hope you'll ... ## Let's Build A Simple Interpreter. Part 12. DevFeed: [Let's Build A Simple Interpreter. Part 12.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2016-12-01T21:20:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Parsing](), [syntax](), [Code](), [identifier]() Tags: [blog](), [code](), [identifier](), [lexer](), [syntax]() ### AI overview Part 12 of a tutorial series explains how to extend a simple interpreter to parse Pascal procedure declarations. It covers procedure syntax, nested declarations, grammar updates, syntax diagrams, and lexer changes for a PROCEDURE token. ### Source excerpt "Be not afraid of going slowly; be afraid only of standing still." - Chinese proverb. Hello, and welcome back! Today we are going to take a few more baby steps and learn how to parse Pascal procedure declarations. What is a procedure declaration? A procedure declaration is a language construct that ... ## Let's Build A Simple Interpreter. Part 11. DevFeed: [Let's Build A Simple Interpreter. Part 11.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2016-09-21T01:15:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Parsing](), [Parser](), [Programming](), [syntax](), [Code]() Tags: [blog](), [compiler](), [how-to](), [lexer](), [parsing](), [recursive-descent-parser](), [tokens]() ### AI overview Part 11 recaps how to build an interpreter by performing lexical analysis, parsing, grammar mapping, recursive-descent parsing, AST construction and traversal, and interpretation of a complete Pascal program. It previews nested procedures and functions, semantic analysis, and control flow. ### Source excerpt I was sitting in my room the other day and thinking about how much we had covered, and I thought I would recap what we've learned so far and what lies ahead of us. Up until now we've learned: How to break sentences into tokens. The process is ... ## Let's Build A Simple Interpreter. Part 10. DevFeed: [Let's Build A Simple Interpreter. Part 10.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2016-08-04T13:15:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Programming](), [Programming language](), [Code](), [Compiler]() Tags: [article](), [blog](), [build](), [code](), [command-line](), [compiler](), [example](), [github](), [programming-language](), [simple](), [types](), [variable](), [variables]() ### AI overview This tutorial continues a series on building a Pascal interpreter. It updates the interpreter to parse and interpret a complete Pascal program, covering program headers, variable declarations, integer and floating-point division, comments, and grammar changes. ### Source excerpt Today we will continue closing the gap between where we are right now and where we want to be: a fully functional interpreter for a subset of Pascal programming language. In this article we will update our interpreter to parse and interpret our very first complete Pascal program. The program ... ## Let's Build A Simple Interpreter. Part 9. DevFeed: [Let's Build A Simple Interpreter. Part 9.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2016-05-01T10:10:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Programming](), [Parsing](), [Parser]() Tags: [blog](), [how-to](), [language](), [programming](), [syntax]() ### AI overview Part 9 of a tutorial series explains how to parse and interpret Pascal programs, including compound statements, assignment statements, variables, and symbol tables. ### Source excerpt I remember when I was in university (a long time ago) and learning systems programming, I believed that the only "real" languages were Assembly and C. And Pascal was - how to put it nicely - a very high-level language used by application developers who didn't want to know what was ... ## Let's Build A Simple Interpreter. Part 8. DevFeed: [Let's Build A Simple Interpreter. Part 8.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2016-01-18T11:10:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Parsing](), [Parser]() Tags: [blog](), [constructor](), [expression](), [extend](), [generate](), [here](), [node](), [rules]() ### 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 ... ## Let's Build A Simple Interpreter. Part 7: Abstract Syntax Trees DevFeed: [Let's Build A Simple Interpreter. Part 7: Abstract Syntax Trees]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2015-12-15T12:00:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Data structures](), [Parser](), [Parsing](), [Concrete syntax tree](), [Code](), [Programming]() Tags: [blog](), [code](), [computer-science](), [data-structures](), [programming](), [programming-language](), [structure](), [syntax]() ### AI overview This tutorial explains why an interpreter for more complex Pascal constructs can use an intermediate representation, focusing on trees and abstract syntax trees. It also introduces parse trees, or concrete syntax trees, and compares their roles with ASTs. ### Source excerpt As I promised you last time, today I will talk about one of the central data structures that we'll use throughout the rest of the series, so buckle up and let's go. Up until now, we had our interpreter and parser code mixed together and the interpreter would ... ## Let's Build A Simple Interpreter. Part 6. DevFeed: [Let's Build A Simple Interpreter. Part 6.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2015-11-02T12:00:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Parsing](), [syntax](), [Code]() Tags: [blog](), [code](), [expression](), [lexer](), [recursion](), [syntax](), [tokens]() ### AI overview This tutorial extends an arithmetic-expression grammar to support parenthesized expressions with arbitrarily deep nesting. It updates the lexer and interpreter to evaluate expressions containing integers and arithmetic operators. ### Source excerpt Today is the day :) "Why?" you might ask. The reason is that today we're wrapping up our discussion of arithmetic expressions (well, almost) by adding parenthesized expressions to our grammar and implementing an interpreter that will be able to evaluate parenthesized expressions with arbitrarily deep nesting, like the expression ... ## Let's Build A Simple Interpreter. Part 5. DevFeed: [Let's Build A Simple Interpreter. Part 5.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2015-10-14T11:00:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Compiler](), [Parser](), [Programming](), [Code]() Tags: [blog](), [build](), [code](), [compiler](), [expression](), [how-to](), [programming](), [programming-languages](), [writing-code]() ### AI overview This tutorial explains how to build an interpreter that parses and evaluates arithmetic expressions. It covers operator associativity and precedence for addition, subtraction, multiplication, and division, using expressions such as "14 + 2 * 3 - 6 / 2". ### Source excerpt How do you tackle something as complex as understanding how to create an interpreter or compiler? In the beginning it all looks pretty much like a tangled mess of yarn that you need to untangle to get that perfect ball. The way to get there is to just untangle it ... ## Let's Build A Simple Interpreter. Part 4. DevFeed: [Let's Build A Simple Interpreter. Part 4.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2015-09-11T11:00:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Parser](), [Programming](), [Parsing](), [syntax](), [generators]() Tags: [blog](), [bnf](), [code](), [generators](), [programming](), [syntax]() ### AI overview Part 4 of a series on building a simple interpreter. It explains how to parse and interpret arithmetic expressions containing multiplication and division, including integer division, and introduces context-free grammars and modified EBNF notation for specifying programming-language syntax. ### Source excerpt Have you been passively learning the material in these articles or have you been actively practicing it? I hope you've been actively practicing it. I really do :) Remember what Confucius said? "I hear and I forget." "I see and I remember." "I do and I understand." In the previous ... ## Let's Build A Simple Interpreter. Part 3. DevFeed: [Let's Build A Simple Interpreter. Part 3.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2015-08-12T11:00:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Parser](), [Programming language](), [syntax](), [Programming]() Tags: [blog](), [how-to](), [parsing](), [programming-language](), [syntax]() ### AI overview Part 3 of a series on building a simple interpreter explains how to parse and interpret arithmetic expressions containing any number of plus or minus operators. It introduces syntax diagrams as visual representations of programming-language grammar and shows how they can guide parser implementation. ### Source excerpt I woke up this morning and I thought to myself: "Why do we find it so difficult to learn a new skill?" I don't think it's just because of the hard work. I think that one of the reasons might be that we spend a lot of time ... ## Let's Build A Simple Interpreter. Part 2. DevFeed: [Let's Build A Simple Interpreter. Part 2.]() Original publisher: [Read original article]() Author: Ruslan Spivak Published: 2015-07-03T11:00:00Z Content type: tutorial Language: en Sources: [Ruslan Spivak]() Topics: [Programming](), [Code](), [Software Engineering](), [Software]() Tags: [blog](), [code](), [compilers](), [development](), [source](), [string]() ### AI overview This tutorial continues a series on building an interpreter by extending a calculator to handle whitespace, multi-digit integers, subtraction, and addition. It explains the code changes, including token handling and position advancement, and provides source code and a sample session. ### Source excerpt In their amazing book "The 5 Elements of Effective Thinking" the authors Burger and Starbird share a story about how they observed Tony Plog, an internationally acclaimed trumpet virtuoso, conduct a master class for accomplished trumpet players. The students first played complex music phrases, which they played perfectly well. But ... [Next page]()