You could save one byte by replacing "0=" with "0<>" (well, except for the name, maybe use "0#"?):

    pop ax
    neg ax     ;sets carry flag if nonzero
    sbb ax,ax
    push ax

And another two bytes in DOCOL:

    ;add ax,4
    ;mov si,ax
    xchg ax,si
    lodsw
    lodsw

Maybe even free up a word register to always hold the address of DOCOL, then you only need two bytes at each colon definition. If it's possible without adding any extra instructions, this should save 4 bytes in total (one stosw in COLON, the DOCOL.addr variable, one lodsw in the above version of DOCOL)