MBASIC Features¶

This document lists all features implemented in MBASIC-2025 (this implementation of MBASIC 5.21).

Language Features¶

Complete MBASIC 5.21 Syntax¶

✓ 100% parser coverage for valid MBASIC 5.21 programs ✓ All data types: Integer (%), Single (!), Double (#), String ($) ✓ Implicit typing via type suffixes ✓ Type declarations: DEFINT, DEFSNG, DEFDBL, DEFSTR

Variables and Arrays¶

Simple variables: A, B$, COUNT%, TOTAL!, VALUE#
Arrays: Single and multi-dimensional with DIM
Dynamic allocation: Arrays allocated as needed
OPTION BASE: Support for 0 or 1-based arrays
Array bounds: Automatic checking for subscript errors

Operators¶

Arithmetic: +, -, *, /, \, ^, MOD Relational: =, <>, <, >, <=, >= Logical: AND, OR, NOT, XOR, EQV, IMP String: + (concatenation)

Control Flow¶

IF...THEN...ELSE - Conditional execution with nesting
FOR...NEXT - Counted loops with STEP
WHILE...WEND - Conditional loops
GOTO - Unconditional branch
GOSUB...RETURN - Subroutine calls
ON GOTO/GOSUB - Computed branches
ON ERROR GOTO/GOSUB - Error handling

Input/Output¶

Console I/O: - PRINT - Output with formatting (;, ,, TAB, SPC) - PRINT USING - Formatted output with format strings - INPUT - Interactive input with prompts - LINE INPUT - Full line input (Note: Graphics LINE statement is not implemented) - LPRINT - Line printer output (Note: Statement is parsed but produces no output - see LPRINT for details)

File I/O: - Sequential files: OPEN, CLOSE, PRINT#, INPUT#, LINE INPUT#, WRITE# - Random files: FIELD, GET, PUT, LSET, RSET - Binary I/O: MKI $/MKS$ /MKD$, CVI/CVS/CVD - File management: KILL, NAME AS, RESET - File queries: EOF, LOC, LOF

Functions (45+)¶

Mathematical: - Trigonometric: SIN, COS, TAN, ATN - Logarithmic: LOG, EXP - Other: ABS, INT, FIX, SGN, SQR, RND

String: - Extraction: LEFT $, RIGHT$ , MID $, CHR$ , STRING$ - Analysis: LEN, ASC, INSTR, VAL - Formatting: SPACE $, STR$

Type Conversion: - CINT, CSNG, CDBL - Numeric conversions - STR$, VAL - String/number conversions

System: - INKEY$ - Non-blocking keyboard input - FRE - Free memory query - POS - Cursor position - PEEK, POKE - Memory access (emulated)

User-Defined: - DEF FN - Single-line functions - Multi-line DEF FN support

For the complete list of all functions, see Functions Index.

Data Handling¶

DATA - Define data values
READ - Read data into variables
RESTORE - Reset data pointer

Program Control¶

Direct Commands: - RUN - Execute program - LIST - Display program lines - NEW - Clear program - SAVE - Save program to disk - LOAD - Load program from disk - DELETE - Delete line ranges - RENUM - Renumber program lines - AUTO - Auto-line numbering mode - BREAK - Set/list/clear breakpoints for debugging

Execution Control: - STOP - Halt execution (resumable) - END - Terminate program - CONT - Continue after STOP - SYSTEM - Exit MBASIC

Error Handling¶

ON ERROR GOTO - Error trap setup
ON ERROR GOSUB - Error subroutine
RESUME - Continue after error (RESUME, RESUME NEXT, RESUME line)
ERR - Error code variable
ERL - Error line number
ERROR - Generate error

Debugging¶

TRON/TROFF - Line tracing
Breakpoints - Set/clear breakpoints (available in all UIs; access method varies)
Step execution - Execute one line at a time (available in all UIs; access method varies)
Variable viewing - Monitor variables (available in all UIs; access method varies)
Stack viewer - View call stack (available in all UIs; access method varies)

See UI-specific documentation for details: CLI Debugging, Curses UI, Tk UI

User Interface Features¶

Curses UI (Default)¶

Full-screen editor with line numbers
Split screen - Editor above, output below
Syntax checking - Real-time error marking
Breakpoint indicators - Visual markers
Auto-numbering - Smart line numbering
Line sorting - Automatic or on-demand
Variables window - View variable values (^W)
Stack window - View execution stack ({{kbd:step_line:curses}})
Help system - Built-in documentation ({{kbd:help:curses}})
Fast paste - Optimized for large programs

Note: Find/Replace is not available in Curses UI. Use the Tk UI for search/replace functionality.

CLI Mode¶

Classic MBASIC interface - Authentic experience
REPL - Read-Eval-Print Loop
Direct commands - All MBASIC commands
Immediate mode - Expression evaluation
Command history (platform-dependent)

Note: Find/Replace is not available in CLI. Use the Tk UI for search/replace functionality.

Tkinter GUI¶

Graphical interface - Windows, menus, toolbars
Syntax highlighting - Color-coded keywords, strings, numbers
Find and Replace - Search and replace text ({{kbd:find:tk}}/{{kbd:replace:tk}})
Menu bar - File, Edit, Run operations
Toolbar - Quick access buttons
Status bar - Program state display

Web UI¶

Browser-based IDE - Run MBASIC in any modern browser
Syntax highlighting - Color-coded editor
Session-based storage - Files persist during browser session only (lost on page refresh)
Three-panel layout - Editor, output, and command areas
In-memory filesystem - Virtual filesystem with limitations:
50 file limit maximum
1MB per file maximum
No path support (simple filenames only)
No persistent storage across sessions
Basic debugging - Simple breakpoint support via menu

Note: Find/Replace is not available in Web UI. Use the Tk UI for search/replace functionality.

See Compatibility Guide for complete Web UI file storage details.

Compiler Features¶

Semantic Analyzer¶

The interpreter includes an advanced semantic analyzer with 18 optimizations:

Constant folding - Evaluate constant expressions at parse time
Runtime constant propagation - Track constant values during execution
Common subexpression elimination (CSE) - Eliminate redundant calculations
Subroutine side-effect analysis - Detect pure functions
Loop analysis - Identify loop invariants
Loop-invariant code motion - Move constant calculations out of loops
Multi-dimensional array flattening - Optimize array access
Dead code detection - Identify unreachable code
Strength reduction - Replace expensive operations with cheaper ones
Copy propagation - Eliminate redundant variable copies
Algebraic simplification - Simplify mathematical expressions
Induction variable optimization - Optimize loop counters
OPTION BASE support - Compile-time array base handling
Expression reassociation - Reorder for better optimization
Boolean simplification - Optimize logical expressions
Forward substitution - Eliminate temporary variables
Branch optimization - Optimize conditional branches
Uninitialized variable detection - Catch potential bugs

These optimizations improve execution speed while maintaining 100% MBASIC compatibility.

See Architecture for details on interpreter vs. compiler modes.

File Format Support¶

BASIC Program Files¶

ASCII text (.BAS, .bas) - Human-readable source
Tokenized (.BAS) - CP/M MBASIC format (partial support)
Line endings: CR, LF, or CRLF (auto-detected)

Data Files¶

Sequential text files - Line-oriented text
Random access files - Fixed-record binary
Binary files - Raw binary with MKI$/CVI functions

Compatibility¶

What Works¶

✓ All valid MBASIC 5.21 programs ✓ CP/M MBASIC program listings ✓ MBASIC file I/O conventions ✓ MBASIC error codes and messages ✓ Line number range: 0-65529

Intentional Differences¶

PEEK/POKE - Emulated (no direct memory access)
INP/OUT - Not implemented (hardware-specific)
USR - Not implemented (machine code calls)
Memory model - Python memory management vs. CP/M
File paths - Modern OS paths vs. CP/M 8.3 format

See Compatibility Guide for complete details.

Platform Support¶

Tested Platforms¶

✓ Linux (Ubuntu, Debian, Fedora, Arch)
✓ macOS (10.14+)
✓ Windows (10, 11)
✓ WSL (Windows Subsystem for Linux)

Python Versions¶

Required: Python 3.8+
Tested: Python 3.8, 3.9, 3.10, 3.11, 3.12
Recommended: Python 3.10 or later

Dependencies¶

Required¶

Python 3.8+ - Interpreter only

Optional¶

urwid 2.0+ - For Curses UI
python-frontmatter 1.0+ - For help system

Development¶

pexpect 4.8+ - For automated testing