f207d74aec
Four roadmap items: - codegen: fix parenthesized string comparison. emit_atom didn't consume the body of a string-literal token (`"`), so for PRINT (A$+B$ < "ZZZ") it emitted a 0 placeholder, advanced one byte, and left "ZZZ" to be reparsed as a variable + extra trailing tokens -- the binary then failed to link with `var_ZZ_sng` undeclared. emit_atom now skips to the closing quote. Separately, the left_type tracking in emit_num_prec dropped VT_STR after a string + string concat (becoming VT_SNG), so the string-comparison codepath skipped when the relational operator arrived. Preserve VT_STR through TOK_PLUS when both operands are strings. Verified: paren string-cmp now compiles and produces the same -1 / 0 result as the interpreter. - compiler: --no-gc-check and --fast-math optimization flags. --no-gc-check skips the per-line gwrt_check_line() (no string-pool GC, no Ctrl+Break trap). --fast-math drops the divide-by-zero guard on `/`; the divisor still goes through (double) so 10/0 produces inf rather than SIGFPE. Both threaded through codegen_opts_t and exposed in --help. --inline-arrays from the roadmap deferred -- larger refactor. - interp: raise static caps on 32-bit / Linux builds. vars 256 -> 1024, arrays 64 -> 256, MAX_FOR_DEPTH 16 -> 64, MAX_GOSUB_DEPTH 24 -> 128, MAX_WHILE_DEPTH 16 -> 64. Codegen FOR_STACK_MAX 16 -> 64. Analysis-pass caps: MAX_LINES 4096 -> 8192, MAX_VARS 256 -> 1024, MAX_GOTOS 256 -> 1024, MAX_DATA 1024 -> 4096, MAX_GOSUB_RET 256 -> 1024. 16-bit DOS keeps the original modest caps via #ifdef _M_I86 -- the MEDIUM model has a single 64KB DGROUP for all static data and the bumped sizes broke runtime startup under DOSBox-X. 16-bit binary grew from 128KB to 132KB from the offset_secs field plus DATE$/TIME$ shift code, well within the FreeDOS budget. - interp + codegen: DATE$ / TIME$ assignment via process-local clock offset. Was a no-op accept-and-ignore. Now sets gw.time_offset_secs (long), and DATE$ / TIME$ / TIMER readers apply it to time(NULL) before formatting. The OS clock is unaffected (would need root). Compiled-binary readers also reference gw.time_offset_secs since libgwrt shares the gw struct. Verified: PRINT DATE$; DATE$="12-31-1999"; PRINT DATE$ shows the expected before/after in both interpreter and AOT paths. After these changes: 72/72 interpreter tests, 68/68 compat, 63/63 compiler tests, DOS smoke under DOSBox-X all pass. Build clean on both Linux (cmake) and 16-bit DOS (build_dos.sh 16).
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 interpretergwbasic-compile-- the ahead-of-time compilerlibgwrt.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.