A very simple script to type macrons, using AutoHotKey.

macrons.ahk

; Hotstrings for typing macrons
; If o is a vowel, i.e. one of (a, e, i, o, u, y), typing ~~o turns into ō pretty much anywhere.
; Typing ~~ followed by a space will produce a naked macron, i.e. ¯.

:*?:~~i::ī
:*?:~~ ::¯
:*?:~~e::ē
:*?:~~o::ō
:*?:~~a::ā
:*?:~~y::ȳ
:*?:~~u::ū