Why doesn't pattern matching on a property of a record compile?

Question

Why doesn\'t pattern matching on a property of a record compile?

type Cell = { X:int; Y:int }

let isNeighbor cell1 cell2 =
    match cell1.X, c         


        

Answer 1

When you do

match cell1.X, cell2.X with
| cell1, cell2

you have created a new cell1 variable, which is cell1.X (an int).

I would probably have just used an if here, or change to | _,_ when ...

Answer 2

As John Palmer already explained, you are shadowing the original parameters. If pattern matching does not feel well suited if-elif-else might be better. If you want to use pattern matching, the following could be helpful:

let isNeighbor { X=x1; Y=y1 } { X=x2; Y=y2} =
    match abs(x1-x2), abs(y1-y2) with
    | 0,1 | 1,0 | 1,1 -> true
    | _ -> false

Remove the 1,1 pattern if diagonal adjacent cells should not be neighbors. And then, there is also Euclidean distance...