evv/gw-basic-2026

Files

Eremey Valetov c317d683fb Compiler: accept unnumbered programs, fix string concat in PRINT

Three fixes that lift seven test programs from skipped to passing,
bringing the AOT compiler harness from 56/56 to 63/63.

- Unnumbered programs (compiler_main.c): src/compiler_main.c skipped
  any line that didn't start with a digit, so direct-mode .bas files
  like hello.bas, math_ops.bas, string_ops.bas (no line numbers)
  failed with "No program lines found".  load_file now auto-assigns
  line numbers (last_num + 10) to unnumbered lines, with overflow
  protection at line 65520.

- String concatenation in PRINT (codegen.c): emit_str_atom had a
  broken concat loop that emitted "; _cat = gw_str_concat(&...
  _cat.sval ...)" — _cat was never declared, so any program with a
  string-literal concat in PRINT (like PRINT "ABC" + "DEF") failed
  to link.  Concat is properly handled by emit_str_expr's outer
  loop; remove the dead/broken code in the atom.  Fixes
  string_ops.bas.

- Transcendental result type (codegen.c): peek_expr_type returned
  VT_DBL for ATN/LOG/EXP/VAL, so PRINT formatted them with 15-digit
  double precision (e.g. 3.141592653589793) while real GW-BASIC and
  the interpreter format the single-precision result as 3.141593.
  Real GW-BASIC's transcendentals are single-precision; only CDBL
  forces double.  Demote ATN/LOG/EXP/VAL to VT_SNG; CDBL stays
  VT_DBL.  Fixes math_ops.bas.

Also: tests/run_compiler_tests.sh now runs the compiled binary from
the project root rather than the tempdir where it was built, so
test programs that reference tests/programs/ via relative paths
(chain_test, common_test, run_file, misc_stmts) resolve their
targets.  Earlier I'd misdiagnosed those failures as ON ERROR
divergence — they were just CWD-dependent path lookups.

Doc/test counts: 56 → 63 in README, docs/index.md, docs/development.md,
docs/roadmap.md.  Roadmap updated to note the compiler now accepts
unnumbered programs.

2026-05-04 16:32:09 -04:00

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GW-BASIC 2026

A portable C reimplementation of Microsoft GW-BASIC, using the original 8088 assembly source (released by Microsoft in 2020) as the authoritative reference.

This is not a transpilation -- it reimplements the algorithms in clean C11 with modern data structures while targeting bug-compatible behavior.

Building

cmake -B build && cmake --build build

Requires a C11 compiler and CMake 3.10+. PulseAudio (libpulse-simple) is optional -- detected at build time for SOUND/BEEP/PLAY support.

Builds three targets:

gwbasic -- the interpreter
gwbasic-compile -- the ahead-of-time compiler
libgwrt.a -- runtime library for compiled programs

Usage

Interactive mode launches the authentic GW-BASIC full-screen editor:

$ ./gwbasic
GW-BASIC 2026 0.17.0
(C) Eremey Valetov 2026. MIT License.
Based on Microsoft GW-BASIC assembly source.
Ok
PRINT 2+2
 4
Ok

Run a program file (ASCII or binary tokenized):

./gwbasic tests/programs/prime_sieve.bas

Compile to a native executable:

./gwbasic-compile tests/programs/fibonacci.bas -c --runtime .

Ahead-of-Time Compiler

gwbasic-compile translates BASIC programs to C source, then invokes GCC to produce native executables linked against libgwrt.a.

Pipeline: .bas → tokenizer → analysis → C codegen → gcc → native binary.

63 of 63 eligible test programs compile via gwbasic-compile and produce output matching the interpreter's golden files. Run bash tests/run_compiler_tests.sh to verify.

# Generate C source
./gwbasic-compile myprog.bas -o myprog.c

# Compile to executable (automatic)
./gwbasic-compile myprog.bas -c --runtime /path/to/gw-basic-2026

Jupyter Kernel

A Jupyter notebook kernel for GW-BASIC with inline Sixel graphics rendering, INPUT support, and Pygments syntax highlighting.

pip install -e .
gwbasickernel-install --user
jupyter notebook  # select "GW-BASIC 2026" kernel

What Works

100% token coverage -- all 144 GW-BASIC tokens are implemented.

Data types: INTEGER (%), SINGLE (!), DOUBLE (#), STRING ($)

Operators: + - * / ^ \ MOD AND OR XOR EQV IMP NOT < = > <= >= <>

Statements:

Category	Statements
Output	PRINT, LPRINT, LLIST, PRINT USING, WRITE, CLS
Variables	LET, DIM, ERASE, SWAP, DEFINT/SNG/DBL/STR
Control flow	GOTO, GOSUB/RETURN, FOR/NEXT, IF/THEN/ELSE, WHILE/WEND, ON...GOTO/GOSUB
Input	INPUT, LINE INPUT, DATA/READ/RESTORE, INKEY$
Program	RUN, CONT, STOP, END, NEW, LIST, CLEAR, AUTO, RENUM, DELETE, EDIT
Sequential I/O	OPEN, CLOSE, PRINT#, WRITE#, INPUT#, LINE INPUT#
Random-access I/O	FIELD, LSET, RSET, PUT, GET, CVI/CVS/CVD, MKI$/MKS$/MKD$
Program I/O	SAVE (binary/ASCII), LOAD (auto-detects), MERGE, CHAIN, COMMON
Event trapping	ON TIMER(n) GOSUB, TIMER ON/OFF/STOP, ON KEY(n) GOSUB
Error handling	ON ERROR GOTO, RESUME, ERROR, ERR, ERL
User functions	DEF FN, RANDOMIZE
File management	KILL, NAME, FILES, MKDIR, RMDIR, CHDIR, SHELL, ENVIRON
Date/time	DATE$, TIME$, TIMER
Screen	LOCATE, COLOR, WIDTH, SCREEN, KEY ON/OFF/LIST
Graphics	PSET, PRESET, LINE, CIRCLE, DRAW, PAINT, GET/PUT (sprites), VIEW, WINDOW, PALETTE, PMAP
Sound	SOUND, BEEP, PLAY (MML)
Memory	DEF SEG, PEEK, POKE, BSAVE, BLOAD
Hardware I/O	OUT, INP, WAIT, MOTOR, STICK, STRIG

Tests

72 interpreter tests, 14 kernel tests, 63 compiler tests -- all passing.

bash tests/run_tests.sh              # interpreter
python -m gwbasickernel.test_kernel  # Jupyter kernel

DOS / FreeDOS

Cross-compiles to DOS with OpenWatcom V2:

wmake -f Makefile.dos16   # 16-bit real-mode (128KB standalone, no extender)
wmake -f Makefile.dos     # 32-bit DOS/4GW  (175KB, requires DOS4GW.EXE)

The 16-bit build runs on FreeDOS, MS-DOS, and compatible systems without a DOS extender. See Getting Started for details.

Documentation

Full Sphinx documentation in docs/:

cd docs && pip install -r requirements.txt && make html

License

MIT License. See LICENSE.

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