Relative coordinates with /function

I have an armorstand. With command blocks, it executes a /function several times... This is the commands in the function file :

setblock ~ ~ ~ air
#Detects if it has reached an obsidian block
execute @s ~ ~ ~ detect ~ ~1 ~ obsidian 0 scoreboard players tag @s add end
tp @s ~ ~1 ~
#if it's not the end, the function is executed again
execute @s[tag=!end] ~ ~ ~ function myfolder:myfunction

It should place air until it reaches the obsidian block, but the air is only placed at the start, where the armorstand executed the function for the first time...