Minizinc在求解过程中跟踪数组

我有一个2d网格，其中某些单元格值会产生不同的分数，我想通过为单元格赋值来最大化分数。是否可以跟踪求解器在求解过程中尝试的每个网格？下面是模型的一个片段，只是为了演示这个想法。

int: i_count;
int: e_count;
set of 1..3: ROW;
set of 1..3: COL;
enum CELL = { U, I, E };
array[ROW,COL] of var CELL: grid;
constraint sum(r in ROW, c in COL)(grid[r, c] = I) <= i_count;
constraint sum(r in ROW, c in COL)(grid[r, c] = E) <= e_count;
var int: assignment_gain = sum(r in ROW, c in COL)(
let {var CELL: cell = grid[r,c]} in (cell = I) * I_SCORE + (cell = E) * E_SCORE
);
solve maximize assignment_gain;
output
["Max assignment_gain: (assignment_gain), with below grid:n"] ++
["(grid[r,c])" ++ if c = n then "n" else "" endif
| r in ROW, c in COL];

我尝试将trace放入assignment_gain语句中，如下所示，但没有成功，输出示例为：

grid[1,1]=X_INTRODUCED_0_, grid[1,2]=X_INTRODUCED_1_, ...

var int: assignment_gain = sum(r in ROW, c in COL)(
let {var CELL: cell = trace("grid[(r),(c)]=(grid[r,c]), ", grid[r,c])} in (cell = I) * I_SCORE + (cell = E) * E_SCORE
);