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Flowlog Documentation (flowlog.c)

This documentation set covers Flowlog: a single-file, single-process ISO-style Prolog system built from flowlog.c and using pthreads for parallelism.

For code navigation, flowlog.c is organized into SECTION NN and SUBSECTION NN.N headings. See the layout map in DEVELOPMENT.md when a doc references a section number.

Flowlog provides three execution engines:

• wamvm (default) - a bytecode VM for compiled clause bodies (still sharing the same unifier and built-ins as wam) (SECTIONS 18/24). It can fall back to wam when a program/query uses unsupported features (or be forced to error via FLOWLOG_WAMVM_REQUIRE_VM=1) (SECTION 24). In VM-only mode, it passes the INRIA ISO suite.
• wam - a WAM-lite engine for fast execution of most ISO-style code (including dynamic database and call-by-variant tabling) (SECTION 23). It can fall back to the interpreter when required.
• interp / tree - a direct interpreter (“tree-walking”) used as the reference/fallback engine (SECTION 22).

What you get

• A self-contained Prolog runtime (flowlog.c) you can compile with any reasonably POSIX C toolchain.
• ISO-style behavior for core language features (terms, control, arithmetic, database, streams).
• An interactive REPL with history and line editing (TTY only).
• Multicore OR-parallelism by default, plus conservative AND-parallelism when supported (see PARALLELISM.md).

Start here

• QUICKSTART.md - build, run, and first query
• CLI.md - command-line + REPL reference
• USER_GUIDE.md - writing and running programs (portable ISO style)
• PARALLELISM.md - parallel flags, safety notes, tuning
• CONFORMANCE.md - conformance goals and test suites
• PREDICATES.md - built-in predicates, evaluables, and Flowlog extensions
• TESTS.md - regression tests and ISO suite runners (full source bundle)
• BENCHMARKS.md - benchmark harnesses and reference programs (full source bundle)

Developer docs

• TECHNICAL_DETAILS.md - runtime model, memory/threads/signals, portability notes
• ARITHMETIC.md - integer representation and arithmetic internals
• IMPLEMENTATION.md - parser, terms, unification, indexing, tabling, OR/AND-par internals
• DEVELOPMENT.md - building, testing, debugging, and contributing
• TROUBLESHOOTING.md - common issues (stacks, threading, performance)