# Curious: How does Prolog "Byte code" compare to .NET IL (and some thoughts about enterprise ready systems) **URL:** \ **Category:** Help!\ **Created:** [August 21, 2019, 3:27pm UTC](https://swi-prolog.discourse.group/t/curious-how-does-prolog-byte-code-compare-to-net-il-and-some-thoughts-about-enterprise-ready-systems/1101 "2019-08-21T15:27:02Z")\ **Posts on this page:** 1\ **Showing post:** 6
**Author:** ![EricGT](https://avatars.discourse-cdn.com/v4/letter/e/f1d935/32.png) [@EricGT](https://swi-prolog.discourse.group/u/EricGT)\ **Post date:** [August 21, 2019, 3:50pm UTC](https://swi-prolog.discourse.group/t/curious-how-does-prolog-byte-code-compare-to-net-il-and-some-thoughts-about-enterprise-ready-systems/1101/6 "2019-08-21T15:50:47Z")
The keyword I use to search the SWI-Prolog source code for where the Prolog predicates are implemented in C is [PRED\_IMPL](https://github.com/SWI-Prolog/swipl-devel/search?q=PRED_IMPL&unscoped_q=PRED_IMPL) The way I think of the code is that what can be done with Prolog is done in Prolog, the low level actions such as [unification](https://github.com/SWI-Prolog/swipl-devel/blob/9ed270918b425d123be31c323366dc5e871f52cc/src/pl-prims.c#L207-L396) are done in C. Then if a predicate needs to be faster it is done with calls straight into C. Sometimes, as Jan notes, the code is so tricky that it is better to implement in C than Prolog. That is why I say AFAIK it does not use a Virtual Machine such as [WAM](https://en.wikipedia.org/wiki/Warren_Abstract_Machine) or an Intermediate Language such as JVM or CIL. I know Jan will correct me if this is wrong and then I will have learned something. Related questions: [How can a foreign language predicate also be a built-in predicate?](https://swi-prolog.discourse.group/t/how-can-a-foreign-language-predicate-also-be-a-built-in-predicate/961) [“decompiled prolog”](https://swi-prolog.discourse.group/t/decompiled-prolog/729) [Efficiency of Prolog](https://www.metalevel.at/prolog/efficiency) * * * > **Personal Notes** > > [vm\_list/1](https://www.swi-prolog.org/pldoc/man?predicate=vm_list/1). > > ```prolog > ?- vm_list(append). > ======================================================================== > append/2 > ======================================================================== > 0 s_trustme(clause(638140)) > ---------------------------------------- > clause 1 ((000001707FC6F2F0)): > ---------------------------------------- > 0 i_enter > 1 b_atom(list) > 3 b_var0 > 4 i_call(error:must_be/2) > 6 b_var0 > 7 b_var1 > 8 i_depart(lists:append_/2) > 10 i_exit > ======================================================================== > append/3 > ======================================================================== > 0 s_list(clause(735160),clause(641508)) > ---------------------------------------- > clause 1 ((000001707FCCDEE0)): > ---------------------------------------- > 0 h_nil > 1 h_void > 2 h_var(1) > 4 i_exitfact > ---------------------------------------- > clause 2 ((000001707FC72790)): > ---------------------------------------- > 0 h_list_ff(3,4) > 3 h_void > 4 h_list > 5 h_var(3) > 7 h_firstvar(5) > 9 h_pop > 10 i_enter > 11 b_var(4) > 13 b_var1 > 14 b_var(5) > 16 i_depart(lists:append/3) > 18 i_exit > ======================================================================== > append/1 > ======================================================================== > 0 i_fopen > 1 i_fcalldetva(-4611686413639185926) > 3 i_fexitdet > true. > > ``` > > Source code: > > [pl-wam.c](https://github.com/SWI-Prolog/swipl-devel/blob/ea88f5f4b6bfe3ad87bbc86a930125fdf2b18842/src/pl-wam.c) > [pl-vmi.c](https://github.com/SWI-Prolog/swipl-devel/blob/ea88f5f4b6bfe3ad87bbc86a930125fdf2b18842/src/pl-vmi.c) > [pl-supervisor.c](https://github.com/SWI-Prolog/swipl-devel/blob/ea88f5f4b6bfe3ad87bbc86a930125fdf2b18842/src/pl-supervisor.c) > [pl-comp.c](https://github.com/SWI-Prolog/swipl-devel/blob/master/src/pl-comp.c) > [pl-export](https://github.com/SWI-Prolog/swipl-devel/blob/master/src/pl-export) > > From: pl-vmi.c > Virtual machine instruction names. Prefixes: > > | I\_ | General instructions | > | B\_ | Body specific version | > | H\_ | Head specific version | > | A\_ | Arithmetic compilation specific | > | C\_ | Control (compilation of ;/2, etc.) | > | S\_ | Supervisor instructions. See pl-supervisor.c | > > References: > > [Logic Programming Implementation - Part I: The WAM](https://www.it.uu.se/edu/course/homepage/logpro/ht04/LP_Impl.pdf) > [Limits on memory areas](https://www.swi-prolog.org/pldoc/man?section=memlimit) - Notes trail stack which is also part of WAM. > [Warren’s Abstract Machine - A Tutorial Reconstruction](http://wambook.sourceforge.net/wam-slides.pdf) - List the basic instructions of WAM such as `put_structure`, `set variable`, `unify_value`, `unify_variable`. > [An Abstract Prolog Instruction Set](http://www.ai.sri.com/pubs/files/641.pdf) > > From `pl-comp.c` > > > This module (pl-comp.c) forms together with the module ‘pl-wam.c’ the complete > > kernel of SWI-Prolog. > > Excerpts from: \_ **Bowen _et al._ , 1983** D. L. Bowen, L. M. Byrd, and WF. Clocksin. A portable Prolog compiler. > > > We have opted for the structure-copying method of [Mellish 80] and [Bryunooghe 80], rather than the structure-sharing [Warren 77]. > > > Our storage management strategy is basically that of [Warren 77], i.e. there is a heap containing the program, a “local” stack for control information and variable bindings, a “global” stack for structures, and a "trail stack which keeps track of when variables are bound so that they can be reset to “uninstantiated” at the appropriate time on backtracking. One change is that a reference count is maintained for each clause so that pointers to clauses can safely be included in asserted terms. > > > As our run-time system is based on previously published work [Warren 77] [warren 80] > > * * * > > EDIT: After responses ([1](https://swi-prolog.discourse.group/t/curious-how-does-prolog-byte-code-compare-to-net-il-and-some-thoughts-about-enterprise-ready-systems/1101/8)) ([2](https://swi-prolog.discourse.group/t/curious-how-does-prolog-byte-code-compare-to-net-il-and-some-thoughts-about-enterprise-ready-systems/1101/9)) by Jan W. > > References: > > [SWI-Prolog Implementation history](https://www.swi-prolog.org/pldoc/man?section=implhistory) > > **Bowen _et al._ , 1983** > D. L. Bowen, L. M. Byrd, and WF. Clocksin. [A portable Prolog compiler](https://www.researchgate.net/publication/273888197_A_portable_Prolog_compiler). In L. M. Pereira, editor, _Proceedings of the Logic Programming Workshop 1983_ , Lisabon, Portugal, 1983. Universidade nova de Lisboa. - Explains low level concepts such as control instructions: `enter`, `call`, and `exit`. > > **Neumerkel, 1993** > Ulrich Neumerkel. The binary WAM, a simplified Prolog engine. Technical report, Technische Universität Wien , 1993 - [The binary WAM, a simplified Prolog engine](http://www.complang.tuwien.ac.at/ulrich/papers/PDF/binwam-nov93.pdf) - Notes design concepts of Prolog abstract machines (as opposed to virtual machine VM) at time, including ZIP. > > EDIT: > > This reminds me of [minProlog](https://github.com/andrejbauer/plzoo/tree/master/src/miniprolog) and specifically the execution engine ([solve.ml](https://github.com/andrejbauer/plzoo/blob/master/src/miniprolog/solve.ml)) > This also reminds me of the MIT open couseware lecture of [advanced data structures](https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-851-advanced-data-structures-spring-2012/) ([videos](https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-851-advanced-data-structures-spring-2012/lecture-videos/)) . There was one in particular but I can’t remember the exact one. --- _[View the full topic](https://swi-prolog.discourse.group/t/curious-how-does-prolog-byte-code-compare-to-net-il-and-some-thoughts-about-enterprise-ready-systems/1101)._