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Building Interpreters Step by Step
A staged plan for building a working interpreter for a small grid language, from loading the program to testing, with the decisions to settle at each stage.
Theory and Tools
Interpreter Implementation
Practical steps and pitfalls when building interpreters.
Arithmetic Edge Cases in Interpreters
How to handle division by zero, negative remainders and integer size in a small interpreter, with worked examples and advice on choosing and documenting behavior.
Avoiding Stack Underflow Surprises
What an interpreter can do when an instruction needs more values than the stack holds: default to zero, halt with an error, or warn, and how to test each choice.
Building a Trace Visualizer
How to print each step of a grid program with pointer position, current cell and stack so you can see a run, with a small Python sketch and formatting tips.
Choosing a Data Structure for the Playfield
Compare nested arrays, flat arrays, hash maps and sparse storage for a two-dimensional program grid, and learn which fits fixed or growing playfields.
Compiling a Grid Program to Another Language
How a compiler can turn the pointer paths of a grid program into ordinary code blocks, and why self-modifying code and direction-dependent cells make it hard.
Handling Input and Output in an Interpreter
How to deal with output buffering, end of input, and the difference between reading a character and reading a number when building a grid-language interpreter.
Loading a Program File into a Grid
How to read a source file into a two-dimensional grid: splitting lines, padding short rows, and handling tabs, carriage returns and unusual characters.
Making an Interpreter Faster
A general look at speeding up a grid-language interpreter: measure first, precompute jumps, cache decoded cells, and keep the cache correct when code changes.
Testing an Interpreter with Small Programs
Build a ladder of tiny test programs that each isolate one instruction, with expected outputs, so you can trust and safely change your grid-language interpreter.
The Fetch and Execute Loop
How the core loop of a grid-language interpreter reads a cell, acts on it and moves the pointer, with a small Python example and the order-of-operations details.
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