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Pack genutils -- prolog/ccstate.pl
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This module provides two kinds of stateful computation, one which undoes state changes on backtracking (run_state//{1,2,3}) and another which preserves state changes on backtracking (run_nb_state//1).

On top this are built two execution contexts which provide mutable references (run_ref/1) and a mutable environment (run_env/1).

 run_state_handler(+Pr:prompt(R), +H:pred(+R,S,S), +G:pred, S1:S, S2:S) is det
Run P in an context where handler H is available process requests with state threaded through DCG style.
 run_state(+Pr:prompt, +P:pred, S1:S, S2:S) is det
 run_state(+P:pred, S1:S, S2:S) is det
Run P in an context that allows set/1 and get/1 to be used to to handle a mutable state, initially S1. The final state is unified with S2. run_state/3 uses the prompt state. State changes are undone on backtracking. run_state(Pr,G,S1,S2) is equivalent to run_state_handler(Pr,handle,Goal,S1,S2).
 run_nb_state(+Pr:prompt, +P:pred, +S1:S, -S2:S) is det
 run_nb_state(+P:pred, +S1:S, -S2:S) is det
Run P in a context where get/1 and set/1 manipulate a mutable state, similar to run_state/3, but state changes are not undone on backtracking. Note that, to ensure preservation of state on backtracking, set/1 saves a copy of the given term, not the term itself. Implementation uses nb_getval/2 and nb_setval/2 with a dynamically generated key. run_nb_state/3 uses prompt state.

Note that using this can be quite expensive if the state is large due to the copying that occurs whenever it is changed.

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

 run_state(Arg1, Arg2, Arg3)
 set(Arg1, Arg2)
 get(Arg1, Arg2)
 app(Arg1, Arg2)
 upd(Arg1, Arg2)