% to weave:
%   noweave -t4 -delay -index example.nw -filter custom-code >example.tex
% 
\documentclass{article}
\usepackage{noweb}
\noweboptions{smallcode}
\topmargin=0pt
\textheight=9in
\def\sub#1{$_{#1}$}
\def\minus{-}
\def\plus{+}
\def\equals{=}
\def\lt{<}
\def\gt{>}
\def\neliac{%
    \catcode`_=\active%
    \catcode`|=\active%
    \catcode`&=\active%
    \catcode`*=\active%
    \catcode`'=\active%
    \catcode`^=\active%
    \catcode`-=\active%
    \catcode`+=\active%
    \catcode`==\active%
    \catcode`<=\active%
    \catcode`>=\active%
    \catcode`/=\active%
}
\bgroup\neliac
\global\def\nwcustomcode{\neliac%
    \global\def_##1{\sub{##1}}%
    \global\def|{$\cup$}%
    \global\def&{$\cap$}%
    \global\def*{$\times$}%
    \global\def'{$\vert$}%
    \global\def^{$\uparrow$}%
    \global\def+{$\plus$}%
    \global\def={$\equals$}%
    \global\def/##1{\(\ifx##1=\ne\else\slash##1\fi\)}%
    \global\def<##1{\(\ifx##1=\le\else\lt##1\fi\)}%
    \global\def>##1{\(\ifx##1=\ge\else\gt##1\fi\)}%
    \global\def-##1{\(\ifx##1>\to\else\minus##1\fi\)}%
}
\egroup

\begin{document}
Here is some actual code from the original Neliac compiler for the
Univac M-460 ``Countess'' computer (written in Neliac, of course):
<<*>>=
DEBUG SCAN:
i = 0: standard compiling location -> i; ;
j = 0: obj prog std last address -> j; ;
i = i(1)j{ [i] = straight jump function | [i] = return jump function:
	fault 9. ; [i](15 -> 29) = 61000_8 & [i](0 -> 14) - bias -> k /= 0:
	{ [k] = 0 | [k] = straight jump function: fault 10. ;  }; ;
l'oop exit:  }. check key sets, turn off flex, clear indices,
key[2] /= 0: dump name lists and stop. exit.
F'AULT 9:
start flex, carriage return upper case, 69 -> lower loop limit,
72 -> upper loop limit, dump a title,
n = 177_8(1)0{ undefined name location[n] = i:
	write undefined name, continue. ;  },
C'ONTINUE: write address, loop exit.
F'AULT 10:
start flex, carriage return upper case,
77 -> lower loop limit, 82 -> upper loop limit, dump a title,
n = 777_8(1)0{ name address[n] - bias = k: write name, go on. ;  },
k -> upper dump buffer[1], dump five number,
G'O ON: write address, loop exit.
W'RITE ADDRESS:
{ 73 -> lower loop limit, 76 -> upper loop limit, dump a title,
i -> upper dump buffer[1], dump five numbers,  }. e'xit: . .
@
And here is the very same code without the \verb"custom-code"
typesetting:\let\nwcustomcode=\relax
<<*>>=
DEBUG SCAN:
i = 0: standard compiling location -> i; ;
j = 0: obj prog std last address -> j; ;
i = i(1)j{ [i] = straight jump function | [i] = return jump function:
	fault 9. ; [i](15 -> 29) = 61000_8 & [i](0 -> 14) - bias -> k /= 0:
	{ [k] = 0 | [k] = straight jump function: fault 10. ;  }; ;
l'oop exit:  }. check key sets, turn off flex, clear indices,
key[2] /= 0: dump name lists and stop. exit.
F'AULT 9:
start flex, carriage return upper case, 69 -> lower loop limit,
72 -> upper loop limit, dump a title,
n = 177_8(1)0{ undefined name location[n] = i:
	write undefined name, continue. ;  },
C'ONTINUE: write address, loop exit.
F'AULT 10:
start flex, carriage return upper case,
77 -> lower loop limit, 82 -> upper loop limit, dump a title,
n = 777_8(1)0{ name address[n] - bias = k: write name, go on. ;  },
k -> upper dump buffer[1], dump five number,
G'O ON: write address, loop exit.
W'RITE ADDRESS:
{ 73 -> lower loop limit, 76 -> upper loop limit, dump a title,
i -> upper dump buffer[1], dump five numbers,  }. e'xit: . .
@ \relax
\end{document}