Of the videos, this is the first session, on reading WEB programs.
Only about 10 minutes of the transcript on the right have been cleaned up. The rest are autogenerated from YouTube.
tangle now—
I'll illustrate TANGLE in a minute if the
computer is up… And if I run
WEAVE on my web file, I get this book—
TeX it and I get this
book. Now let’s see: is the computer—
computer seems to be up. So let’s try to
switch over to the computer screen and
I’ll illustrate what what tangle looks
like when it’s running. One thing you
have to do in order to use WEB is
to have a TANGLE program working. So we
have the lights down and see if you can
see the computer screen. Now let’s see... a
minor right file
okay can you see at the bottom of the
screen there I’ve said something with
tangle it’s the contrast won’t be very
very good but it’s asking me for all
let’s see we should be able to get that
up higher in the screen in a minute it’s
asking me for the name of a web file and
I will call for tango web that’s on my
area web the cave it that’s when you for
a change file. The change file is where
you will put in your modifications that
that you would want to use at your
particular installation. I'll just use
null for a change file. Now can anyone
see that at all? OK? Now my output
is output on tango PSC for example
that’s what we use for suffix is there
and it’s asked me for a pool file also
and I don’t need a pool file in this
case. Now pool file is where you it would
put strings if there were strings
strings in double quotes in the listing
that have more than willing flung
because tango will will do that not
known as see if we can watch it
operating here is printing out. As it
gets to a starred module these are the
ones that have come out in boldface type
and in the table of contents in your web
listing it prints out the number of that
module as it gets to it so we can see
what it’s doing. And it’s tangling itself
right now because tangling from tangle.web
web so this is converting the web
description of the program into a pascal
program and first of all it reads the
whole thing into memory into a very
compact form inside of itself and now
it’s right in the output file every time
I prints a dot it’s done 100 lines of
output I’ll puff Pascal output ok so
there 500 ok
guys and so then when we get the output
file that we should be able to run
Pascal on that. Here it’s also giving us
some statistics about—let’s see I can
put that up higher on the screen—it told
how large it’s it needed for its memory
and it it stored that whole TANGLE
program in approximately 18,000 tokens
uh close our it tho those are over
18,000 bytes to represent the tango
program in its contact form or plus the
what is called byte memory and the TANGLE
programs is in is in one of those
handouts that you have.
Now since we did
that successfully let’s try the same
thing on TeX I will try to handle TeX
and here we just... TeX is a much larger
program but I have to show you
illustrated graphically so we do this so
TeX.web and again I won’t use any
change file and we’ll go to text a scowl
and now are the pool file will put it in
text tool and our text that pool at
first and then in at our particular
system extensions like pool can only
really be three letters long so that’s
going to be called POO. Alright so it’ll
go run for a while but bit but it’ll be
generating the it’ll be generating a
Pascal source for this program.
Now
the WEB—the listing that you have
of TeX begins with the table of
contents. So very first as you open that
covers you’ll see that there’s 55 parts
to the program, and number one is the
introduction and the last one is the
index. And so these are the major
sub-structures
as far as TeX
82 is concerned. We’re going to be
talking about for example string
handling psyche part for that will be
one of the things to talk about the next
hour of the lecture. I want to to
recommend that when you read this you
start in section one and then go to
number two and so on instead of starting
at section 400 and something like this.
Now there are some places to start that
are worse than others and I think the
section on alignment is the
worst of all. If you try to start reading
TeX by learning how it does \halign, I
think that it might take well four
hundred hours instead of 40 hours to
understand what’s going on. Because
alignment is done in something like
posthypnotic suggestion by somebody who
plants little ideas into the
other parts of TeX and every once in a
while they come into action and do the
right thing. But it stands
in the background most of time in it and
it sort of lets everything else happen
and automatically will rise to the right
occasion at the proper time.
That’s the kind of thing that I
couldn’t write first and you shouldn’t
read first. but especially I intended it
to I actually presented this pretty much
in the order that i wrote the program
are almost been almost in that order
because I I wrote the program in a way
that I felt it called to be written. it’s
saying that now before I go any further
my mind won’t be at ease unless I do
this I want to know how this is going to
happen I got to do this now and that or
somehow I don’t know exactly why I felt
that way but I did usually feels rather
strongly or what needs to be done next
and I think also for reading it similar
take similar questions would be in your
mind that this is what you might want to
know next just as to what to do.
So it’s a combination of a bottom-up and
a top-down approach where at first I go
by them up and build up a lot of tools
that I’m going to need later I know I’m
going to need those tools but as I work
on a particular tool I probably approach
the building of that tool from a
top-down direction.
Now the thing is a
total of twelve hundred and forty four
modules at least at the present time and
after i finished debugging it will
probably be 1245 the and these modules
they all are numbered, so you can see
that usually we get several modules on a
page, and as I turn over you can see
different modules.
each one has a nice big bold-faced
number on it and up in the middle of the
page here you’ll be able to see the part
number and the module number so for so
there will be a little section sign in
between so like this is part 35 in
module number 6 52 okay and this is the
part that’s doing typesetting a math
formula. This whole listing of course was
generated by my computer automatically
from the web file. Now at the end we
have an index and the index shows every
occurrence of every identifier in the
program and then there’s underlined ones.
The underlined ones indicate where that
identifier was defined so let’s take
this other things in the index besides
identifiers and talk about those in a
minute but let’s take this one empty so
empty is defined here in module 5 88 so
588 is underlined it’s used in all of
these modules here we are going to look
them all up but let’s check us check out
588 and see what empty is is doing in
588 and it turns out that there’s a
definition of empty here both in in text
where explains that what empty means
math type empty indicates a field with
Nova
or you can’t see the few things that
people on the videotape can see and I’m
I’m I’m sorry I’ve been assuming that
you could you could read a little bit
what I saw what I see on my monitor here
okay I’m let’s can we turn the lights
down and put the end and give them on
this screen what what I see on the
monitor is that possible can you can you
see anything that we’re all in all I see
you it’s it’s it’s incompatible because
they need a light to get the to get the
camera to read this okay well forget
I’ll meanwhile by the way TeX is
tangling up to module number 749 and
we’re time sharing and getting fifteen
percent of the machine in the Lotus 4.5
ok now the anyway are saying that if we
look in the index you if you look in the
index then that should refer you to
where things are defined and and all the
uses of them except if the if letter is
only one if it’s only one letter long
then the index only gives the underlined
references to it it doesn’t give
anything else so if you see in the index
for example I probably have a letter F
all by itself and so under F there will
be lots of underlined entries for F well
that’s wherever f was used what quest
was declared probably as a parameter to
a procedure or local variable in a
procedure if there’s any fonts because
the one letter identify as our intended
or probably used so often and nobody
would care to see them in the index now
that other things that appear in the
index are error messages so if you if
you see an error message come out of
TeX and you want to say well where in
heck was that error message generated
then this will tell you what module
to find that and a few few things you’ll
find it well reserved words you don’t
often find in the index unless I
specifically said I wanted to indicate
that the word begin is used in this
module in some interesting way but
usually Pascal’s other words so of
course won’t be indexed by the time the
book is published we expect that there
will be a lot more entries in the index
that will that will keep key you into
where TeX does various operations so if
you want to see where it is TeX handle
some something like lowering a box or
something like that you might look under
you might look up the index under
lowering a box and it might be there I’m
going to try to go through this and this
as I do with other books and try to
figure out what ought to go into the
index of the book but I haven’t done
that yet very much so the other kinds of
index entries that are just in roman
type there are only a few of them so far
and those those will be like you know if
there’s one in entry here for chinese
characters and it says chinese
characters are discussed in modules 128
457 500 and you can if you’re interested
in extending text so that it would deal
with chinese characters suggestions for
doing that are in those are most modules
now each module except the index has a
same basic structure to it and it’s a
three-part structure: there’s the first
part is TeX, second part is definitions
of macros, and the third part is pascal
now the gnarls modules have this have
all three parts they can be empty you
might not have a TeX part might not
have a definition part you might not
have a Pascal part but if but you never
have more than one TeX parking you
never have a definitions after the
Pascal park you never have a TeX part
of you know it always has that order
TeX definitions Pascal
and they might be absent this is
something that to turn out to be a
fairly good fairly easy thing not only
to implement but also to it was
approximately where I was writing code
when I when I tested this place out when
I when I was sketching out the ideas of
web last phone um now the TeX part then
is expository it’s supposed to supposed
to explain either a what the whole idea
of what’s going on now and in the future
or it will explain some less obvious
point about about the code that follows
perhaps telling you the environment of
the code telling you what you what’s
supposed to be true at this point I
reminding how we got here things like
that states I’m kind of an invariant of
a loop that will be there explain why
that Luke might be expected to terminate
saying why it why I didn’t do such and
such they comment at the beginning
depend on what I think are what is it
worth saying I try to think of something
interesting to say in every module that
has passed caltex that’s going to be
contributed to the main program anyone
the definition part defines macros or
talk a little bit more about that in a
minute that’s a key thing to
understanding a program written in web
and then of course then the Pascal part
at the end is Pascal code I try to shoot
for about 12 lines of code in in these
as a maximum sometimes I go up a little
more but I try to keep it to something
that you can understand as a unit the
idea being that if you if you have
faithfully come into this module from
from the previous ones you should be
able to know enough about it about the
current subproblem and what and what
you’re supposed to do in this module to
fully understand it in terms of the in
terms of these 12 lines just advice by
looking at these back maybe
if you’re I would go back and forth over
the 12 line a few times and when you say
oh yes I got this this makes sense to me
so the the modules are small enough that
the that you can perceive this structure
and perceive the whole idea they refer
to other modules in different ways let
me see take a sort of a random I just
turned to module 1 180 which is on page
59 of your of your of your handout this
is I just chosen at random and it said
display the value of glue set of P and
so that’s a little module that his
country is actually I might tell you
that it’s used when we’re trying to
print out p is pointing to a box we’re
trying to print out what the glue
setting is this is the ratio of how much
the glue has to expand and if the glue
is going to be expanding by a nonzero
amount we want to indicate that amount
of expansion because we’re going to wear
this is part of the diagnostic output to
explain what wanted text data structures
in national art form so the code then
says if glue side uppy is not 0 then we
will print comma glue set now in those
cool quotes in the print statement print
double quote comma comma glue set you
are you see that this is at one of those
strings that I mentioned before strings
with double quotes Pascal use a single
quotes for strings tango makes those
strings and puts them into a string pool
file in fact it has finished now and it
said it wrote 897 strings to the string
pool so there are there are eight
hundred ninety seven different strings
in the in the program if if if I use the
same string several times it will of
course do it only once now tango
converts that to an integer and the
integer that it uses starts at 128
because the
20 21 27 are we are reserved for the
single character strings and there’s an
internal code there’s a specific and
it’s essentially ascii code that’s used
so that if you had a double quote a on
double quote that always refers to ascii
code abate it doesn’t refer to your
local and to dicker whatever code you
might be using that always refers to
ascii code of a will talk about
characteristic problems later on when we
talk about strength but that’s oh so
anyway this is a number so when I says
print double quote blue sec and double
quote that’s really in the Pascal file
is going to say Prince 428 or some some
other integer will be in the Pascal
program then we check and see if the
glue sign of P is shrinking and we print
a minus sign into indicated that the
glue is shrinking instead of stretching
c and then we have problems to see
whether what we’re going to print out
some value if it’s real large then we’re
going to print out a greater than 20,000
or less than 20,000 somebody anyway
that’s the way the program works here
and it says that the bottom this code is
used in section 1 78 so if you need to
know where this module was applied it
was over here in modules 178 178 indeed
applied it here display the value of
glue set P and in that module it that
module is display box and so p is
pointing to a box and we and we and we
haven’t in this module the problem is
how to display a box and that breaks
down into subproblems and so let’s just
read through that codes that you get the
idea so you look at see what kind of a
box it is it’s going to be either an H
list Notre realest know we’ll talk about
data structure to say afternoon but that
means it’s in each box or vbox
essentially so we either going to print
the hov the H is going to be the ASCII
code h because this is a 1 1 letter
string you see
print escape means it’s going to prefix
it by a backslash it’s going to print a
backslash in an age otherwise if it’s a
V list notice printed back section of e
otherwise there’s some Club unset node
which is used in alignments and then we
have a box and a left parenthesis and it
will print the height of the box as a
scale number we’ll talk about these
things later and then it says Prince of
dimensions the height the depth and
width and then it would check if it’s an
unset note it has to do something
special display special fields of the
unset node P&S module 179 which we don’t
care about for the purpose for our
purposes now we can say okay that’s
going to be something that’s going to
display those special fields otherwise
we will display the value of blue set P
that’s the one and out we looked at
first and that also say whether it’s
stretching or shrinking unset notes
don’t have glue sets that’s why we do it
differently and furthermore I don’t have
shift amount this this is whether if the
box will shift it up or down or
something like that and so we check and
see if it’s shifted so that finishes
this module 178 it referred you see two
modules 179 or 180 but if we had to
actually stick the code in there it
would be a distraction so we don’t want
it so for now we concentrate on what
what are you doing it display a box you
have to go through that many operations
and then you’ve done it now this code is
using section 1 77 which indeed is
called display node p and it breaks down
it’s a case statement that has many sub
cases the first three cases where
ageless node V list no done said node
said display box p that’s where we do
this or we had to display a rule or
insertion or all these things we have to
possibly display and there’s another
module here that fits in to the case
statement called cases of show notice
that arise in Emily’s Sony this is when
you’re trying to display something in
math about and it only occurs in math
mode so we don’t even write it in this
part of the TeX program since we only a
person reading it doesn’t know about
mass mojet in fact when I wrote this
part of it I didn’t know about math
knowledge it myself so i just made a
module saying well i’m going to handle
those cases later and in 596
that the arm will will have indicated
what you will the exposition will have
explained what what math mode is like
and so there will be display
instructions in there and that will be
patched into the program by tango at
this point so we’ll have a case
statement that also includes other cases
for things like square root signs and so
on that have to be displayed and then it
says other cases print unknown node type
and this is something I'll talk about
with respect to what you do in case
statements in pascal if they it agree
that really means all other cases that
haven’t been listed here and this code
was used in 176 and if we look at 176 it
doesn’t tell us where it was used in 176
it just ends at the bomb says what
doesn’t talk say where it was used if it
doesn’t say where the code was used this
means it’s it’s really on bottom level
this is part of the whole Pascal program
itself and so some the things in bottom
level are strung together in the order
that they appear here so this this
module 176 will follow the previous code
for bottom level in in the program any
questions so far on this now that the
macro definitions is something I’ve got
to talk about next let’s take a simple
case of macro there are three kinds of
definitions and they all say define and
the one is is numeric definition and and
then there are there then there are
definitions that substitute with or
without parameters those are the three
kinds of definitions let’s see if I can
find a example okay numeric definition
I’m on page 51 s module number 156 has
lots of numeric definitions I’m laying
out the memory and I’m giving symbolic
names to specific parts in the memory so
i defined zero glue oh this is not a
numeric definition I’m sorry it has a it
has three lines yeah it’s an equivalence
instead of an equal sign how this means
it’s a text substitution because I if
it’s just an equal sign it means that
it’s a numeric thing which I’ll compute
at at tangling time but this is a text
substitution because men base is a
compile time constant that’s that that
art it’s something anyway that that I
didn’t think I I could necessarily know
so I I’ve used three hours here and then
i define Phil glue to mean zero glue +
blue specks I’ve anyway those are these
are things that have been defined
elsewhere this is an example of a
definition and whenever I say camp head
later on or it’s going to mean hi ma’am
base plus 3 and this means this will be
a more mnemonic way to refer to tamp
head it’s and the comments as it’s a
head of a temporary list of some kind so
each of these things is we try to
explain it in words as as we define them
on the previous page you’ll see a simple
numeric definition define unset node as
13 so that’s the type for an unset node
and that’s followed by the other two
kinds of definition so we have all three
of them in that module that’s nice the
glue glue or shrink is to be substituted
by shift amount which by the way is in
macro itself so eventually will
propagate down to two low level Pascal
code blue stretch of its parameter is
mem of that parameter plus six dot FC
this allows us to to refer to Pascal
structured types in a way that’s that’s
a mnemonic indicating that we’re really
looking at are the sixth this the you
know the seventh word of a of something
that stuck starts in locating a given
location and we’re looking at it as a as
a dot SC field of that word and that n
if we were rewriting text for some other
some other memory configuration we would
only have to change this definition on
glue stretch and to say how we actually
are representing it in whatever language
we’re really programming in because the
rest of the program just talks about
glue stretch of something and doesn’t
know that it happens to be in words
something plus six that so these these
are the three kinds of macros the the
constant macros are restricted that
these numbers can’t get too large i
think it’s something like 15 bits plus a
sign so that the so that i shouldn’t be
i shouldn’t define with an equal sign
something to be I’ll never defile an
equal sign something that’s a that’s a
number are like 50,000 I can do 30,000
okay though the advantage of those small
numbers is that I can do arithmetic on
them and not put parentheses around the
soap if you do text substitution you can
have some troubles if you try to say- a
macro and then that macro has been
defined to be X plus y without
parentheses but if X but if it’s the
macro has been defined with equal signs
and x and y are numbers so it will add
those numbers together and it’ll work
now now I don’t understand how I know
when I look reading my program which of
these identifiers is a macro and which
isn’t somehow I’ve never been confused
by it but press because I wrote the
program and it’s something that is I in
the back of my mind to experiment with
it would there be a use for some type of
graphic distinction between names that
have been defined as a macro our names
that are really there really Pascal
identifiers on the low level everything
eventually propagates into a Pascal code
but
who knows but but when I’m reading a
program on you know I’m here in the
middle of module number 700 something
and it refers to glue stretch am I
supposed to know that how do I know
that’s not a procedure call oh it’s
really it has thus it you know it looks
like it might be a procedure call with a
parameter it was really a macro call
with the parameter well partly yeah I
think it’s because I’m when I’m
referring to boo stretch I’m I
presumably know that it means that it’s
a certain feel of a record and I’m
always referring to feel the records by
via macros so that I can have a symbolic
way to refer to them that’s doesn’t that
isn’t too closely tied to Pascal
language itself but anyway some of the
identifiers you see in the program are
passed in the Pascal program others are
our macros and fu as we if you refer to
the index of course it tells you where
it’s defined and you can always check
exactly what it means act now I’ve
written this so that in the final Pascal
program no to identify as we’ll start
with the same first seven letters so so
on he has called rule says that they
have to be distinct in their first eight
but I I made it seven partly this helps
me helps catch typographic errors
because if two things agree to seven if
I have a typographic air and and it
tango will print out that there was that
these two variables have conflicting
names and it probably was that I that I
made it a mistake in typing that after
after the first seven letters but it
also it’s just the because I’ve heard of
compilers that that actually put this
extra restriction on it the first seven
should be unique but this also gives a
clue as to whether a name is is a macro
name or not because macro names don’t
have to be distinct in therefore they
can they can be a hundred letters long
and and the first nine nine letters can
agree because macro names are done by
tangle not by Pascal and I implemented
for a comparison of those names so
whenever I have a long identifier which
looks like it’s it has very high chance
of conflicting with in its first seven
let it with something else and that’s
another dead giveaway that it’s a macro
name because I would never dare use such
a such an identifier and freeze those
those valuable first seven letters for
some other purpose like I don’t know
we’ll see examples of that anxious okay
now let’s take a look at the very
beginning of the program and see how it
gets how it gets started as I said the
right way to read this is is starting at
module one and going through I’m not
going to be giving you homework
exercises in these lectures but I would
encourage you to to do some reading
tonight and tomorrow night you’ll
probably get more out of the lectures on
Thursday and Friday the introduction
here is primarily historic and and there
is one definition at the bottom of the
page that defines the banner string and
here’s something that will be source of
one of your system dependent changes
presumably you will you will change this
so that at the version number will also
indicate that that this is the vax
version or something else and then this
right now its version minus one minus
point two five because it’s not debug
yet okay then I talked about the idea of
system dependent codes and oh and other
things that are in the index here in
section 3 and and one of the things I
mentioned here in section 3 is this idea
of an index entry that’s called dirty
paske there were a few places where I
did things that aren’t considered kosher
in pasco and if we look up dirty pesca
on the index that will show you those
modules and the modules will try to
justify why they did the thing they did
usually it was for debugging purposes
where you had to fetch out a wreck
not knowing what it was because
something is going to gone wrong but
anyway if your compiler is going to
complain about those you want to you
want to know about it part 4 is where we
actually get going and and that end into
the program and it’s and so here’s where
we first start this is the first pascal
text modules 123 didn’t have any pascal
text there was this one definition and
the very first thing well we have a
definition here that i could explain em
type i defined to be t ampersand Y
ampersand p + % Eve and this is a
special web thing that will will
concatenate different identifiers
together without spaces between them and
I’m calling an m-type is t ype the
reason is that i wanted very much to use
type as one of the macros that i was
going to define later but it’s a
reserved word in pasco and so in order
to do this I can define m-type for the
one or two places where I needed to use
pass cause reserved word and then ever
then afterwards like I get to use type
myself because this is a format which is
a special kind of a definition that says
that the m type identifiers should be
treated like Pascal treats type and type
should be treated like Pascal treats
true so that will so for formatting
purposes I can make those kind of
definitions also that’s that’s a little
thing for web now the program itself
starts here with compiler directives in
module nine then program statement and
gives the name of TeX it doesn’t have
any file names mentioned there because
if it did on our past call anyway the
user would have to type in filenames at
that point and that’s not the way TeX82
does things. Then comes the labels and
there’s a listing for labels in the
outer block section 6 constants in the
outer block types in the outer block
this is where i use my m type and you
notice now it gets formatted
facing and then VAR this Global’s in the
outer block then there’s a procedure
declaration for the initialization and
initialized procedure is going to be
called to get things going and then
there’s a module called basic printing
procedures which we had to declare very
early in the game and error handling
procedures which we also have to declare
early because any errors can occur
almost anywhere you have to declare your
error handling procedures soon but while
you’re doing air is you have to print
out what the area is so you needed the
printing things even earlier and that
incidentally you can force a discipline
that when I’m printing anything out I
got to do something that’s not going to
that’s not gonna have a chance of air is
going wrong so so when I write my print
procedure I’m not supposed to overflow
any buffers or anything that would cause
an error message that would get that
they might get into the loop okay now
that’s the way the program starts and
module five explains how it continues
namely ollie magis from now on is going
to we’re going to have more decorations
of procedures and finally there’s going
to a place called start here where we
start and that’s going to be way at the
end because we just a build-up procedure
after procedure at the procedure doing
the things that take is supposed to do
and then I start here it’s going to say
do it with something like that are going
to call initialize and a few other
things so and then it will also tell how
to die gracefully at the end so these
modules are further explained later on
and I have special things declared in
module 7 that’s for four different
versions of the seven and eight which
are four different versions of the same
program this is all one program some of
you have experience with the period the
previous kinds of TeX and the end the
and there were three programs there was
TeX there was a system dependent module
an ax and a pre processing module all
three functions are combined in this one
now and even a few more and these and in
order to select out
and things we we can change these
definitions of these modules here i have
debug and backwards debug and if i put
code between debug and backwards debug
it will be commented out normally
because I’ve declared debug to be at
sign left brace which is a real left
grace to go into the program and
backwards the guard to be a real right
grace this by incidentally tango will
will now change left braces to other
symbols so that it won’t so still be a
valid Pascal comment in between those
two braces but these two break or if
these were inside of other braces these
wouldn’t you actually come out as races
they come out of the brackets but this
is this is now will will comment out all
the code between debug and backwards
debug similarly there’s statistics and
backward statistics that comment out
code that would slow TeX down but will
keep information about how big it’s
tables are getting and when you’re
installing a system you want to find out
how large how much of your memory is
actually being used you’d like to see
these statistics but it gets a repulsive
for people printer model a time it slows
assistant done I think well maybe four
or five percent but maybe you wouldn’t
want to pay that four or five percent if
people aren’t using the statistics so
that can also be commented out and it’s
shown as commented out here then here is
similarly is is is the other version of
TeX in it and backwards in it these are
things that are only present in the
initialization version of TeX the one
that you need to get started because it
loads all of the hash tables with the
primitives and loads preloads formats
preloads macros so that it can put
everything into a condensed file for
efficient starting out of the production
program so you have two versions of TeX
production program a peck and the
initialization called any time and to
make any tech you you I you’ve got it
because this is this is not commented
out
but to get the production version you
have to put you have to change this to
braces and you do this in your change
file you never change the web file
protect you just you just make a change
file for any type a change file for
production TeX and you run tango with
one or the other now let’s see that
ahead there will be other changes
probably between these also because any
technical 12 to allow yourself more room
maybe for hyphenation tables since I you
want to see how big those are going to
be and and then afterwards when you have
a production TeX you know that the
hyphenation table is not going to be
very big you can cut that that part time
parameter down so those are the three
things that can be compiled compiler
directives is something rather most
Pascal compilers if the comment starts
with a dollar sign it will do something
special like check-rein strangers or not
and so and so on so I I’ve done that no
I don’t know what time it is i I can’t
see the clock in the back is can someone
tell me what engaged it’s ten-thirty ok
so i got only a few more minutes before
we break we started five minutes late
the so let’s take a look at the what the
computer is done since we did start it
out there and so you see that it came to
a conclusion and in fact the where it
says idle 25 minutes that means I
haven’t done anything for 25 minutes but
the two in front of it says that that
was two seconds to minutes of CPU time
so it took exactly two minutes of cpu
time to do this tangling on on its deck
10 and it had a little more than 4,500
lines of Pascal code and the the numbers
here the number of tokens here was was
more like a hundred and ten thousand
bytes in order to do the compressed
thing in memory and also called tokens
and then things that were called bites
those are generally strings
and and names of identifiers and there’s
lots of those too so this is a this is a
rather large order for tango fulfilled
but it is in too bad now let’s take a
look at the Pascal program that that was
was generated so that’s c-tick esco now
this should be forty five hundred and
some lines long and taking a while to
read in two for the etiquette to read it
all in because that’s a page oriented
during the larger the page is that on
your takes now I just wanted to count
how many semicolons are in this listing
so we can get some idea as to how long
is I’ve never done this before I wanted
to find out how big tit how big TeX is
so it starts out with with the program
and you’ll see also that there’s things
in braces there indicating what module
that came from so if you can read the
brace nine that that was two hours
because this court was generated by the
compiler directives which was module
nine and module nine it it commented
something out and then that bracket
there was the comment with a break for
the brace inside of a bracket so then we
get a program TeX and it says label
then the comment 6 says that those
labels in the outer block are in module
six you see how that works now let’s see
if I if I search for a search for a
semicolon now I’m going to search and
see how many semicolons it confined just
to see on any semicolons Ernest listing
this is the way the Pascal program looks
and its 4556 lines right now but it’s
all uppercase letters except where we
have a in strings if somebody’s Pascal
doesn’t accept uppercase letters they
would have to do system dependent
changes on the strings in quotes you can
see that text sources has a few
lowercase letters they’re all the lines
are 72 characters
or less ok now it’s found 10,000 928
semicolons and so it’s approximately
11,000 statements and declarations in
this program except that the word else
also contributes so if i search for else
I can find some more so let’s try else
see if see how many occurrences of else
there and program 664 so that has enough
okay so so approximately not quite
12,000 statements and declarations are
are in its program and okay I the
corresponding figure for sale tech was
5,000 so I’m just trying to understand
the difference now now say effect used
declarations they would declare a lot of
variables at the same time with commas
in between them instead of having one
line for declarations so that might
account for is but the if you look at if
you want to know about the size of this
compared to pee Teck it’s a little
shorter then then the p-tech bus assists
debt so it’s a it’s approximately it’s
actually gotten smaller than the than
the existing version of text i believe
the compilers will would be able to
handle okay well if there are any quick
questions i can handle them otherwise
we’ll start I will break for half an
hour and I can’t seek well yet there’s
one or a format you give identifier
equivalent to another identifier the
first identifier is the is the one you
want to be using the second one is the
one that that that you wanted to format
like so if you so ID so i formatted
debug as begin I said format debug equal
be equivalent to begin and that means
that when texas debug it should enter a
new level of indentation and put it in
boldface like it does for begin and send
backward see bug i made like n
and and so why not what usually when i
define I and identify a macro I’ll just
I just want it to be treated in the
normal garden vanilla the normal way
that all identify the treaty but if I
want some special treatment I can say
treat it like a certain Pascal reserved
word yeah the web manual is eight pages
long so those rules are all given there
in detail because at the very beginning
we have as you know in most programs at
the very beginning you there are
features that are only used once for
understanding TeX itself those little
fine points of web programming aren’t
going to be aren’t going to be important
but if you want to know exactly what’s
going on then then most those things to
arise another yes
okay the question is why use Pascal
constants in some place in defined
numbers in others and the answer is I
made Pascal constants in the places
where I felt the user could could change
in that compile time and nothing else to
go wrong and so this was the distinction
is available I think of valuable
distinction to have so the things that
are constant in that Pascal program you
should be able to change that number and
recompile without doing anything to your
web file or anything now but the to have
the actual definitions it was possible
for me to get around a lot of other of
class cause restrictions for example
Pascal doesn’t allow you two to have an
array boundary that something minus one
and by the lake by declaring it as a web
macro i can subtract one from entangle
will do the arithmetic and and it will
not find in my program so that’s why i
I’ve used web to get around these these
problems with Pascal language it’s done
correctly and Ada and I wouldn’t have
had to do that neighbor I might have
been a different a different here on
some other time so a while
all the format of a change file is that
is that lines should match doesn’t see
can we get that up on let’s take a look
at TeX change we didn’t use a technical
change there but them now this is a page
oriented editor and so the first page is
an index to the rest of the is there in
phenix the rest of the file and they
should ban so it shows you the first
line of page to the first line of page
three and so on his page to which which
is the first change i made and then I
just repeat verbatim align that’s in
`tex.web` and then and then I made a
ni made a correction so the first line
matched then it goes on until the line
it says at sine Z at the bottom there
and and you see I I might change here
was only to put an s in the version
number it’s a version minus 0.25 s for
Stanford I guess or sale or something a
sale stands for Stanford artificial
intelligence lab and and then these our
index entries by the way here extensions
to text I’ve this at sign up they’re
always in is something goes in the index
and I and at sign up arrow system
dependencies changes for sale in medium
caps pond I every time I put some in my
change file i also put index entry
saying this is this is a change that i
made so that when i look at the index
that i would we from this I could find
all that all the modules that I’ve
changed now the next module starts out
with debug and backwards debug and in I
copy it exactly except that I did change
its poor for debugging also that the it
isn’t braces it’s blank
and so on so all of these changes you
start out with a thing here I use a
special switch on RD on our compiler a
double you switch which makes it catch
the kind of areas that IBM pesco catches
that our compiler doesn’t ordinarily
catch yes yes yes yeah that’s the idea
that the change file is a small number
of changes that will probably that that
you can keep on fiddling with until you
get it to work with your present to dot
web file then when you get the real web
file later on probably is that your
change if I will still work with it I’m
so lawless this independent chain with
this I could extend to multiple change
files but we hit the but since we’re
listing all our files at the beginning
of the tangled run right now we only
have exactly one web file in one change
file every time we run tanga ok so we
saw this existing file is given on the
tape that you get for TeX as an example
of one changeup all that was done I’ve
done I’ve made it here if you look at I
example like the memory max has been
changed to 1000 that’s not enough to do
any user jobs protecting but it’s very
good for debugging because when you’re
debugging you want to you want the
program to get into its complicated
cases where it has to try hard be fun to
find a free amendment how that first
happened a few months later ok question
over there
okay yeah so so as soon as it finds a
matching line like the 60 watt so tango
reads this is this first line into a
buffer the following parameters and so
on keeps it in a buffer every time it
reads in a line from the other file from
the web file it compares those two
buffers if they agree think it will will
do something like not care about blank
spaces at the end of something but if
they agree exactly then it starts
reading the change file and continues
the change file until it comes to add
sine Z at the beginning of the line it
deletes all the stuff in the web prob
till the beginning of the next module in
this way you would be able to substitute
more than one module for 48 you know
your change ball could generate five
modules for the four lonely the one in
the other but we discourage this because
then all your numbers will be off and
you end why you know why do I do that so
at the very end the just before the
index there’s a module called system
dependencies and this is and so so
that’s where the system dependent
changes this module should be replaced
by changes to the program that are
necessary in and here’s where you try to
gather all of the all of the changes
that are going to require new modules to
be made that way all the this will be
the only one that changes the numbering
system and only index then we’ll really
be Miss numbered nothing else will five
will be go bother you there okay well we
better break now and meet again at
eleven o’clock sharp for the second
session. Thanks very much.
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