I have difficulty finding the way to access values from prolog key-value pairs.
gas-[2, 3, 1, 1, 3]
Above is an example of my pair, gas is a key, and the list is value. The reason I use this A-B format is because the term -(A, B) denotes the pair of elements A and B. In Prolog, (-)/2 is defined as an infix operator. Therefore, the term can be written equivalently as A-B. from this.
I want to get the list just by 'gas'.
This is done using SWI-Prolog (threaded, 64 bits, version 8.1.24) on Windows 10
?- use_module(library(pairs)).
true.
First an example of constructing the pairs from just a key and value.
?- pairs_keys_values(Pairs,[gas],[[2,3,1,1,3]]).
Pairs = [gas-[2, 3, 1, 1, 3]].
Now that the syntax of what is expected for key-value pairs is known,
extract a value from a pair given a key.
?- pairs_keys_values([gas-[2,3,1,1,3]],[gas],Value).
Value = [[2, 3, 1, 1, 3]].
EDIT
After looking into this more perhaps what you want instead is not key-value pairs but Association lists See: library(assoc): Association lists
?- list_to_assoc([a-1,b-2,c-3],Assoc),get_assoc(b,Assoc,Value).
Assoc = t(b, 2, -, t(a, 1, -, t, t), t(c, 3, -, t, t)),
Value = 2.
Using your example gas-[2,3,1,1,3]
?- list_to_assoc([a-1,gas-[2,3,1,1,3],c-3],Assoc),get_assoc(gas,Assoc,Value).
Assoc = t(c, 3, -, t(a, 1, -, t, t), t(gas, [2, 3, 1, 1, 3], -, t, t)),
Value = [2, 3, 1, 1, 3].