First, make a 3x3x3 vector field with Kirin's Ruler from viewtopic.php?t=14 . You can make it larger or smaller to enlarge or shrink the effect, but I find 3x3 to be the magic size. Arrange for it to be on the stack, either by Reify from the same, or using the Stygian techniques. This will demo the latter, but for a trinket I usually use the former.
The structure of the loop is: for each position, if its dot product with the user's look vector is zero, and there is a block there, break it. Block presence is tested by raycasting in the +Y direction and checking if it is equal. The hammer can be made larger or smaller by adjusting the vector field used. I recommend not attempting to write this until you have a focus or ideally several.begin Stygian preparation; omit for trinkets with Reify
end Stygian preparation
begin Stygian data segment
put vector field here
end Stygian data segment
If desired, you can alter the section to do more involved operations. I have a variant with for exchanging blocks; if you do more than one symbol, delete the between and .