Pico

Pico is a small interpreted language for learning and quick numeric scripting. This repository contains a minimal C++ interpreter with a straightforward lexer, recursive-descent parser, and tree-walking evaluator. Source files use the .ds extension (Pico “dot source”). If you pass a path with no extension (e.g. myapp), the runner will try myapp.ds when the first path does not exist.

Features

• Arithmetic — +, -, *, /, % (modulo), unary -, parentheses
• Numbers — Integer and decimal literals (e.g. 3, 3.14)
• Strings — Double-quoted string literals for print
• Variables — let name = expression and assignment name = expression
• Built-in — print expression writes to standard output
• Programs — Multiple statements separated by newlines or ;
• CLI — Run a file, use -e for one-liners, optional --tokens for lexer debug output
• I/O & timing — read (one line from stdin → number if the whole line is numeric, otherwise text), rand n (uniform random integer from 1 through n, for dice-style rolls), sleep ms (pause for a whole number of milliseconds, up to 24 hours)

Pico-only ideas (what makes it a bit different)

• that — After any print, let, assign, trace, times, or bare expression, the last meaningful value is stored. Use that like a pronoun: let x = 2 then print that + 3. You cannot assign to that (it is not a variable).
• n times … — English-style counted repetition, e.g. 3 times print "hi" or (1 + 2) times print that. The count must be a non-negative whole number.
• trace expr — Prints a step-by-step evaluation log for expr (numbers, strings, variables, operators) and still returns the result like a normal expression.
• read / rand / sleep — Good for tiny games and scripts: e.g. let name = read, let d6 = rand 6, sleep 500. See examples/play.ds.

License

This project is open source under the MIT License.

Requirements

• A C++17 compiler (GCC, Clang, or MSVC)

Build

From the Pico directory:

g++ -std=c++17 -O2 -o pico main.cpp lexer.cpp token.cpp parser.cpp node.cpp interpreter.cpp run.cpp error.cpp context.cpp symbol_table.cpp value.cpp strings_with_arrows.cpp utils.cpp

MSVC (Developer Command Prompt):

cl /std:c++17 /EHsc /Fe:pico.exe main.cpp lexer.cpp token.cpp parser.cpp node.cpp interpreter.cpp run.cpp error.cpp context.cpp symbol_table.cpp value.cpp strings_with_arrows.cpp utils.cpp

Usage

pico [options] [file]
pico -e "code" [options]

Option	Meaning
-h, --help	Show help
-v, --version	Show version
-e, --eval STR	Run source STR
--tokens	Print lexer tokens (debug)

If neither -e nor a file path is given, the interpreter reads test.ds in the current working directory.

Examples

./pico examples/hello.ds
./pico -e "print 2 + 3 * 4"
./pico --tokens test.ds

You can also run pico myapp and it will open myapp.ds when myapp has no file extension and does not exist as a bare path.

Language sketch

let x = 10
x = x + 1
print x
print "done"
print (x % 3)

trace (x + 1) * 2
3 times print "tick"
print that
2 times print 5
print that + 2

See examples/uniques.ds for a short demo of that, times, and trace.

Project layout

Path	Role
main.cpp	CLI entry
lexer.cpp, parser.cpp	Front end
interpreter.cpp, run.cpp	Evaluation
value.cpp, symbol_table.cpp	Runtime values and variables

Contributing

Issues and pull requests are welcome. By contributing, you agree that your contributions are licensed under the MIT License.