The main purpose is to preseve as much information as possible. 

TeX is written using "literate programming" WEB system. WEB is 
intended to keep sources and documentation together. Additionaly 
WEB provides substantial macro capabilities. To get executables 
or printed documentation requiers a few processing stages. Using
`web2c' setup they look as follows:
WEB --> Pascal --> C --> executable
WEB --> TeX --> dvi --> printout
The WEB to Pascal conversion is done using `tangle' program, while 
Pascal to C conversion uses convertor specially writen for `web2c' 
system. At first glance this gives us C equivalent to WEB sources. 
However, even short look at converted code make clear that what 
we get is not the source code. Namely, there is no comment, all 
strings are gone, labels have no menmonic value. Comparing with 
WEB source we see that macros got expanded, decreasing readability
and hampering maintainence. Our goal was to have editable source. 
We were not able to get comments trough conversion -- WEB source 
consists of interleaved code and description blocks. `tangle' 
rearranges code blocks quite extensively and we felt that it was 
not practical to move descriptions together with code (description
would loose continuity anyway, and huge tekst block would interrupt
program flow). What we do have is comments containing cross-references
to WEB source. We prevented most macros from expansion, we 
preserved strings and retained symbolic labels.

Convertion stages:
 - remowe definitions from tex.web
 - protect strings so that tangle will not eat them
 - use tangle with new change file, designed to 
	make Pascal file syntatically correct
 - correct Pascal file (strings, re-add protected parens)
 - convert with p2c
 - correct (remove dummy variables and functions)

Some issues:
 - Pascal file must be syntically correct
 - many WEB macros are l-values, so we expand those macros to 
   dummy variables (if no parameters) or to form 'f(x)^' with 
   dummy pointer valued function. 
 - WEB macros have only one (block of) parameter(s). Multiparameter 
   macros are simulated using additional macros and recursion