For the player code at game maker : STEP = type in
if place_free(x,y+1) {gravity = 0.5} else {gravity = 0}
gravity_direction = 270 if vspeed > 10 {vspeed = 10} if keyboard_check(vk_right)&& place_free(x+4,y){x+=4} if keyboard_check(vk_left)&& place_free(x-4,y){x-=4} if keyboard_check_pressed(vk_up)&&!place_free(x,y+1){vspeed=-7}
and in the collision with the wall type :
if vspeed>0&&!place_free(x,y+vspeed){move_contact(270)}
vspeed=0