commit	dc6d8f6f5a59956fb65dd84b065c16a4290dcbee	[log] [tgz]
author	Sketch🕴️ <skallywag@sketch.dev>	Sat Feb 28 20:45:13 2026 +0400
committer	Sketch🕴️ <skallywag@sketch.dev>	Sat Feb 28 20:45:13 2026 +0400
tree	6d5086d7146fe6017e6218c4a48ed1b91072ad49
parent	5337c2bc7ab93112e7edd4c772d98987ba596e49 [diff]

lexer: recognize identifiers, comma, and equals tokens

- Add identifier scanning: starts with letter/underscore, continues with
  letters/digits/underscores. Produces Ident tokens.
- Add comma and equals to single-char token switch.
- Add isLetter() helper.
- Add 9 new tests covering: single ident, multi-char ident, ident with
  digits, ident with underscore, comma, equals, function definition
  syntax, function call with args, multi-param func def, func call in
  expression.

2 files changed

tree: 6d5086d7146fe6017e6218c4a48ed1b91072ad49

README.md

matheval

A math expression evaluator with an interactive REPL, written in Go.

Features

Arithmetic operators: +, -, *, /
Parentheses for grouping
Floating point numbers (including .5 syntax)
Correct operator precedence (* and / bind tighter than + and -)
Left-to-right associativity
Clear error messages with position reporting

Build

go build -o matheval ./cmd/matheval

Usage

Run the REPL:

./matheval

Then type expressions:

>> 2 + 3 * 4
14
>> (2 + 3) * 4
20
>> 7 / 2
3.5
>> 1 / 0
error: division by zero

Press Ctrl+D (EOF) to exit.

You can also pipe input:

echo "2 + 3" | ./matheval

Architecture

Input string → Lexer → Parser → AST → Evaluator → Result

Package	Responsibility
`token`	Token types and data structures
`lexer`	Tokenizes input string
`ast`	AST node types (`NumberLit`, `BinaryExpr`)
`parser`	Recursive-descent parser
`evaluator`	Walks AST and computes result
`repl`	Read-eval-print loop

Grammar

expr   → term (('+' | '-') term)*
term   → factor (('*' | '/') factor)*
factor → NUMBER | '(' expr ')'

Tests

go test ./...

This runs unit tests for each package plus integration tests covering the full pipeline.