Sinclair ZX Spectrum micro-PROLOG

This repository preserves the Sinclair ZX Spectrum micro-PROLOG distribution and contains a literate resurrection of its Z80 interpreter source.

The maintained source is under src/. It is split into thirteen architecture-oriented modules and assembles to the exact original 14,200-byte interpreter image.

Build the TAP

Requirements

• Python 3
• GNU Make
• either z80asm or pasmo

On Debian or Ubuntu:

sudo apt install python3 make z80asm pasmo

Only one assembler is required for a normal build. From the repository root:

make

The build automatically selects z80asm first, then pasmo. The results are:

build/pcode.bin          byte-exact interpreter image
build/micro-PROLOG.tap   complete loadable distribution tape

Select an assembler explicitly when needed:

make build-z80asm
make build-pasmo
# or:
make ASSEMBLER=pasmo

To build with both assemblers, compare their outputs, verify the known SHA-256, and confirm that the reconstructed TAP is byte-for-byte identical to tapes/micro-PROLOG.tap:

make verify

Remove generated files with:

make clean

No external TAP utility is needed. tools/build.py assembles the interpreter, replaces its block in the preserved distribution tape, recalculates the TAP checksum, and verifies the final file.

Binary identity

Interpreter address:  0x6000–0x9777
Interpreter size:     14,200 bytes
Interpreter SHA-256:  35cb4bde74ddbfe75875bdfa339e18a7fdf320526f31d2dbcb0862271b5b7174

Distribution TAP size:     53,266 bytes
Distribution TAP SHA-256:  a9908f53eaecc51144e9f059833e7e55f5c7e06ca3c3c512833bf409b4de0d86

Source layout

Module	Original range	Responsibility
00_definitions.asm	no bytes	ROM, tags, workspace and structure definitions
01_boot_and_executor.asm	6000–6311	cold start, supervisor restart and evaluator
02_clause_unification_and_allocation.asm	6312–6712	clause selection, frames, unification, trail and allocation
03_garbage_collector.asm	6713–6992	non-moving mark-and-collect garbage collector
04_term_io_and_parser.asm	6993–710C	term output, tokenizer and parser
05_lexical_tables.asm	710D–7224	lexical classifications and variable alphabet
06_devices_and_line_editor.asm	7225–7588	devices, console callbacks, RFILL and line editor
07_type_predicates.asm	7589–7662	type predicates, FAIL and NEW
08_modules_dictionary_and_database.asm	7663–7FF4	cut, modules, dictionaries and relation database
09_graphics_and_machine_io.asm	7FF5–83AB	graphics, sound, keyboard, display and ports
10_supervisor_programs.asm	83AC–8B14	permanent compiled micro-PROLOG supervisor
11_arithmetic.asm	8B15–9477	reversible arithmetic and decimal engine
12_cassette_file_system.asm	9478–9777	cassette file buffering and block I/O

The source uses descriptive global names for callable routines and permanent objects, and dot-prefixed local labels for internal control flow. Extensive comments, pseudocode, and worked examples explain the logical execution core, including clause retry, unification, trailing, cut, and garbage collection.

Preserved material

The repository also retains the original historical assets:

• tapes/ — TAP and TZX distribution images;
• tape-raw/ and blocks/ — individual library records;
• snapshots/ — prepared emulator snapshots;
• utilities/ — extracted micro-PROLOG utility programs;
• cpm/ — CP/M disk image;
• Reference Manual.md — programmer's reference manual.

Background and resources

micro-PROLOG is a compact logic-programming system developed for early microcomputers and marketed by Logic Programming Associates. The ZX Spectrum edition combines an assembler interpreter with a library of optional programs such as SIMPLE, MICRO, EDITOR, TRACE, and MODULES.

Useful historical references:

• ZX Spectrum micro-PROLOG Programmer's Reference Manual
• Spectrum micro-PROLOG manual
• The Purple Planet: Micro-PROLOG for the Spectrum 48K

Original disassembly command

The historical root source was produced with:

z80dasm -a -t -l -g 24576 -b blocks.txt prolog.bin > prolog.asm

The maintained src/ tree is the subsequent byte-exact semantic reconstruction, not a fresh linear disassembly.