Need an example of Record Syntax in mercury -

i new mercury , trying wrap head around record syntax, reference manual place have encountered , leaves me mystified:

term ^ field1(arg1) ^ field2(arg2, arg3) equivalent field2(arg2, arg3, field1(arg1, term)).

could please real-world example?

record syntax syntax sugar, , manual trying explain how transformation record syntax mercury's normal syntax works. fine if you're trying find out how implement record syntax, not helpful if want learn how use it.

i recommend ignoring (arg1, ...) stuff in parenthesis - i'm not sure if it's part of syntax , i've never seen use it.

lets create structure representing points on cartesian plane.

:- type point     --->    point(                 pt_x        :: int,                 pt_y        :: int             ). 

pt_x , pt_y field names allow retrieve values of point's fields. example:

format("the point's x coordinate is: %d\n", [i(point ^ pt_x)], !io), format("the point's y coordinate is: %d\n", [i(point ^ pt_y)], !io), 

we can retrieve value , assign new variable.

x = point ^ pt_x, 

and can update 1 field without having write out whole point again.

newpoint = oldpoint ^ pt_y := newy, 

where things little bit more complicated when used state variable notation, there's syntax sugar occurs.

move_up(d, !point) :-     newy = !.point ^ pt_y + d,     !point ^ pt_y := newy. 

note when read value use !.point, state variable "the current value". , when updated have written:

!:point = !.point ^ pt_y := newy. 

however syntax sugar allows write:

!point ^ pt_y := newy. 

i hope helps. there many more examples throughout mercury source code:

https://github.com/mercury-language/mercury

and ohther mercury projects, note github language tagging broken, many objective-c files detected mercury , many mercury things detected other files:

https://github.com/search?utf8=%e2%9c%93&q=language%3amercury&type=repositories&ref=advsearch&l=mercury