# Inline subterm naming syntax (was: Syntax for unify-and-remember in head?) **URL:** \ **Category:** Request For Comments\ **Created:** [September 1, 2021, 1:43am UTC](https://swi-prolog.discourse.group/t/inline-subterm-naming-syntax-was-syntax-for-unify-and-remember-in-head/4360 "2021-09-01T01:43:29Z")\ **Posts on this page:** 1\ **Showing post:** 3
**Author:** ![EricGT](https://avatars.discourse-cdn.com/v4/letter/e/f1d935/32.png) [@EricGT](https://swi-prolog.discourse.group/u/EricGT)\ **Post date:** [September 1, 2021, 9:03am UTC](https://swi-prolog.discourse.group/t/inline-subterm-naming-syntax-was-syntax-for-unify-and-remember-in-head/4360/3 "2021-09-01T09:03:36Z")
> [@dmchurch](#): > > That’s all I can think of at the moment, though I’m sure I’ve missed something I still have to digest what you wrote in more detail but upon a first cursory readthrough this comes to mind. Effects on the [Byrd Box model](https://www.swi-prolog.org/pldoc/man?section=byrd-box-model) and possible [added ports](https://www.swi-prolog.org/pldoc/doc_for?object=prolog_trace_interception/4). * * * Is the proposal only for deterministic code, e.g. could the clauses be rewritten using [single sided unification](https://www.swi-prolog.org/pldoc/man?section=ssu)? The patterns @peter.ludemann and you show remind me of [C# Deconstructors](https://docs.microsoft.com/en-us/archive/msdn-magazine/2016/connect/net-framework-what-s-new-in-csharp-7-0) and [F# Pattern Matching](https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/pattern-matching) which leads to [Algebraic Data Types](https://en.wikipedia.org/wiki/Algebraic_data_type). Is this where you are headed? * * * I gave your post a like. The like is not to be interpreted as my liking the proposal, instead a like by an admin will give it more points toward being put in the e-mails for those that don’t visit the site regularly. * * * > **Personal Notes (Click triangle to see details)** > > * * * > > > violates DRY > > DRY -Don’t Repeat Yourself ([Wikipedia](https://en.wikipedia.org/wiki/Don%27t_repeat_yourself)) > > * * * > > [optimise\_unify](https://www.swi-prolog.org/pldoc/man?section=flags#flag:optimise_unify) > > SWI-Prolog Documentation 2.18.3 [Indexing for body code](https://www.swi-prolog.org/pldoc/man?section=indexbody) > > * * * > > Displaying the VM Instructions > > File: `examples_optimise_unify_true.pl` > > ```prolog > :- module(examples_optimise_unify_true, > [ > display_record/1 > ]). > > :- set_prolog_flag(optimise_unify,true). > > display_record(Record) :- > Record = record(_, _, _, _), > format('Record: ~p~n', [Record]). > > display_record(record(A, B, C, D)) :- > format('Record: ~p~n', [record(A, B, C, D)]). > > ``` > > ```prolog > ?-current_prolog_flag(optimise_unify,Optimise_unify),clause(examples_optimise_unify_true:display_record(_),Body,Ref),clause_vm(Ref,VM_instructions);true. > > Optimise_unify = true, > Body = format('Record: ~p~n', [_17216]), > Ref = (0000000006F3BAE0), > VM_instructions = [ > vmi(h_functor(record/4), 2), > vmi(h_pop, 1), > vmi(i_enter, 1), > vmi(b_atom('Record: ~p~n'), 2), > vmi(b_list, 1), > vmi(b_argvar(0), 2), > vmi(b_nil, 1), > vmi(b_pop, 1), > vmi(i_depart(system:format/2), 2), > vmi(i_exit, 1) > ] ; > > Optimise_unify = true, > Body = format('Record: ~p~n', [record(_20546, _20548, _20550, _20552)]), > Ref = (0000000006E01250), > VM_instructions = [ > vmi(h_functor(record/4), 2), > vmi(h_firstvar(1), 2), > vmi(h_firstvar(2), 2), > vmi(h_firstvar(3), 2), > vmi(h_firstvar(4), 2), > vmi(h_pop, 1), > vmi(i_enter, 1), > vmi(b_atom('Record: ~p~n'), 2), > vmi(b_list, 1), > vmi(b_functor(record/4), 2), > vmi(b_argvar(1), 2), > vmi(b_argvar(2), 2), > vmi(b_argvar(3), 2), > vmi(b_argvar(4), 2), > vmi(b_pop, 1), > vmi(b_nil, 1), > vmi(b_pop, 1), > vmi(i_depart(system:format/2), 2), > vmi(i_exit, 1) > ] ; > true. > > ``` > > File: `examples_optimise_unify_false.pl` > > ```prolog > :- module(examples_optimise_unify_false, > [ > display_record/1 > ]). > > :- set_prolog_flag(optimise_unify,false). > > display_record(Record) :- > Record = record(_, _, _, _), > format('Record: ~p~n', [Record]). > > display_record(record(A, B, C, D)) :- > format('Record: ~p~n', [record(A, B, C, D)]). > > ``` > > ```prolog > ?- current_prolog_flag(optimise_unify,Optimise_unify),clause(examples_optimise_unify_false:display_record(_),Body,Ref),clause_vm(Ref,VM_instructions);true. > Optimise_unify = false, > Body = (_20=record(_96, _98, _100, _102), format('Record: ~p~n', [_20])), > Ref = (0000000006A1CDA0), > VM_instructions = [ > vmi(i_enter, 1), > vmi(b_unify_var(0), 2), > vmi(h_functor(record/4), 2), > vmi(h_pop, 1), > vmi(b_unify_exit, 1), > vmi(b_atom('Record: ~p~n'), 2), > vmi(b_list, 1), > vmi(b_argvar(0), 2), > vmi(b_nil, 1), > vmi(b_pop, 1), > vmi(i_depart(system:format/2), 2), > vmi(i_exit, 1) > ] ; > > Optimise_unify = false, > Body = format('Record: ~p~n', [record(_3908, _3910, _3912, _3914)]), > Ref = (0000000006E227E0), > VM_instructions = [ > vmi(h_functor(record/4), 2), > vmi(h_firstvar(1), 2), > vmi(h_firstvar(2), 2), > vmi(h_firstvar(3), 2), > vmi(h_firstvar(4), 2), > vmi(h_pop, 1), > vmi(i_enter, 1), > vmi(b_atom('Record: ~p~n'), 2), > vmi(b_list, 1), > vmi(b_functor(record/4), 2), > vmi(b_argvar(1), 2), > vmi(b_argvar(2), 2), > vmi(b_argvar(3), 2), > vmi(b_argvar(4), 2), > vmi(b_pop, 1), > vmi(b_nil, 1), > vmi(b_pop, 1), > vmi(i_depart(system:format/2), 2), > vmi(i_exit, 1) > ] ; > true. > > ``` > > * * * > > SWI-Prolog is not based on WAM VM instructions but ZIP VM instructions. > [ref 1](https://www.swi-prolog.org/pldoc/man?section=implhistory) > [ref 2](https://swi-prolog.discourse.group/t/curious-how-does-prolog-byte-code-compare-to-net-il-and-some-thoughts-about-enterprise-ready-systems/1101/8) > Bowen _et al._ , 1983 - " A portable Prolog compiler" - (ResearchGate PDF [download](https://www.researchgate.net/publication/273888197_A_portable_Prolog_compiler)) > Neumerkel, 1993 - “The binary WAM,a simplified Prolog engine” ([pdf](http://www.complang.tuwien.ac.at/ulrich/papers/PDF/binwam-nov93.pdf)) > > * * * > > SWI-Prolog VM Instructions at the C level > [pl-comp.c](https://github.com/SWI-Prolog/swipl-devel/blob/master/src/pl-comp.c) > [pl-wam.c](https://github.com/SWI-Prolog/swipl-devel/blob/master/src/pl-wam.c) > [pl-vmi.c](https://github.com/SWI-Prolog/swipl-devel/blob/master/src/pl-vmi.c) > > * * * > > Ref: [pl-vmi.c](https://github.com/SWI-Prolog/swipl-devel/blob/984bb191bb1c989d4fc930f558ae0906bfbbc339/src/pl-vmi.c#L115-L122) > > ```plaintext > Virtual machine instruction names. Prefixes: > I_ General instructions > B_ Body specific version > H_ Head specific versin > A_ Arithmetic compilation specific > C_ Control (compilation of ;/2, etc.) > S_ Supervisor instructions. See pl-supervisor.c > > ``` > > * * * > > SWI-Prolog VM Instructions > > virtual machine variables: [pl-vmi.c](https://github.com/SWI-Prolog/swipl-devel/blob/984bb191bb1c989d4fc930f558ae0906bfbbc339/src/pl-vmi.c#L61-L83) > > > Within the scope of this file, the following virtual machine variables are available. > > \* FR > > Current environment frame > > \* NFR > > Next frame (used to share in various calling instructions) > > \* BFR > > Backtrack frame: current choicepoint > > \* PC > > Program Counter > > \* ARGP > > Argument pointer > > \* CL > > Running clause (= FR-\>clause) > > \* DEF > > Running definition > > H\_FIRSTVAR: [pl-vmi.c](https://github.com/SWI-Prolog/swipl-devel/blob/984bb191bb1c989d4fc930f558ae0906bfbbc339/src/pl-vmi.c#L799-L806) > > > H\_FIRSTVAR: A variable in the head, which is not anonymous, but > > encountered for the first time. So we know that the variable is still a > > variable. Copy or make a reference. Trailing is not needed as we are > > writing in this frame. ARGP is walking the argument list, but is always > > in some compound term as H\_FIRSTVAR is not generated for plain variables > > in the head. > > B\_UNIFY\_FIRSTVAR: [pl-vmi.c](https://github.com/SWI-Prolog/swipl-devel/blob/984bb191bb1c989d4fc930f558ae0906bfbbc339/src/pl-vmi.c#L1221-L1248) > > > B\_UNIFY\_VAR, B\_UNIFY\_EXIT: Unification in the body. We compile A = Term > > into one of the following: > > Normal: A is firstvar: > > B\_UNIFY\_VAR B\_UNIFY\_FIRSTVAR > > > > B\_UNIFY\_EXIT B\_UNIFY\_EXIT > > We need B\_UNIFY\_FIRSTVAR for the debugger as well as for > > clearUninitialisedVarsFrame() in pl-gc.c. When in debug mode we simply > > create a frame for =/2 and call it. Note that the `slow unify’ mode must > > be consistently applied in B\_UNIFY\_VAR and B\_UNIFY\_EXIT, which is why we > > copy the global value into a local variable. > > TBD: B\_UNIFY\_CONST , > > B\_UNIFY\_VAR , > > Note that the B\_UNIFY\_FIRSTVAR assumes write mode, but this is > > unimportant because the compiler generates write (B\_\*) instructions. > > > > Invented by dmchurch. > > > > ```plaintext > B_INLINEVAR > H_INLINEVAR > > ``` > > > * * * > > > (Prolog) Conformity Testing I: Syntax ([ref](https://www.complang.tuwien.ac.at/ulrich/iso-prolog/conformity_testing)) > (Works for ISO/IEC JTC1 SC22 WG17) > > * * * --- _[View the full topic](https://swi-prolog.discourse.group/t/inline-subterm-naming-syntax-was-syntax-for-unify-and-remember-in-head/4360)._