GW-BASIC–like Interpreter (C++)

A lightweight, cross-platform GW-BASIC / MSX-BASIC–inspired interpreter written in modern C++.

This project focuses on language compatibility, correctness, and clarity, not on emulating old hardware.
It is designed to run in a modern terminal while preserving the look & feel and semantics of classic BASIC.

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✨ Features

✅ Language Core

• Line-numbered programs
• Immediate (REPL) mode
• Numeric (Double) and string variables ($)
• Expressions with correct precedence
• IF / THEN
• GOTO / GOSUB / RETURN
• FOR / NEXT (supports nested loops)
• DIM (1D arrays, implicit DIM 0..10)
• READ / DATA / RESTORE
• DEFINT
• REM comments

✅ Built-in Functions

• Math: SIN, COS, TAN, ATN, LOG, EXP, SQR, ABS, INT, SGN
• Strings: LEN, LEFT$, RIGHT$, MID$, CHR$, ASC, STR$, VAL
• Random: RND() (GW-BASIC–style behavior)
• Time: TIME / TIME()
• Formatting: TAB(n)

🎲 Random Numbers

• RND() → next random number
• RND(0) → repeat last random number
• RND(x > 0) → next random number
• RND(x < 0) → reseed using abs(x)
• RANDOMIZE [seed] supported

⏱️ Timers

• ON INTERVAL n GOSUB line
  • n is in 1/60th second ticks (GW/MSX compatible)
• INTERVAL ON
• INTERVAL OFF
• INTERVAL STOP
• Safe interrupt handling with proper resume semantics

🖥️ Screen & Terminal

• PRINT with , and ;
• INPUT
• CLS
• LOCATE row, col [, cursor]
  • cursor: 0 = hide, 1 = show
• COLOR f, b (ANSI-mapped, GW-BASIC color palette)
• Cursor-aware printing (TAB, column tracking)

🧾 Program Editing

• Built-in line editor
• Handles insertion, deletion, navigation

⌨️ REPL

• Immediate execution
• RUN, LIST, NEW, CLEAR, CONT
• QUIT / EXIT
• Ctrl+C stops a running program (returns to REPL)
• UP arrow recalls last command

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🛠️ Build

macOS / Linux

clang++ -std=c++20 -O2 *.cpp -o basic
./basic