what i should probably do is add 'hooks' just before newlines have been yielded
so you can look at the previous line and say hey it's an include
let's start lexing that instead

unify/optimize ascii/asciiz/byte/halfword/word into BIN directives
also lex strings to binary strings, why not

;pseudo-instr for offsets not within 0x8000 range?
addiu   at, t0, 0x7FFF
sb      t1, 0x62FE(at)
;versus
sb      t1, r0+0xE2FD(t0)

directive aliases, are these right?
    DB = 'BYTE',
    DH = 'HALFWORD',
    DW = 'WORD',

add basic command-line interface (patch.lua)

improve writer performance (just copypaste what you did in patch.lua)

allow generation of shared object files (zelda overlays specifically)
 -> http://wiki.cloudmodding.com/oot/Overlays#Relocation_Entry_Format

macros:
    add 'em
    implement push/pop/jpop as macros
    be able to point to specific args of push/pop using variables

procrastinating the heck over:
    lex expressions in Lexer instead of its own separate lexer
    write tests for everything (try to focus on code paths and edge cases)
    make breaking changes to syntax for the sake of macros, expressions etc.
    (and keep a branch with the old syntax for good measure, feature-frozen)

low priority:
    improve parser terminology
    add delay slot warnings
    externally document more stuff like syntax
    add file-reading directives (e.g. for automatic hook injection macros)