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author | Hans Hagen <pragma@wxs.nl> | 2020-07-02 17:28:32 +0200 |
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committer | Context Git Mirror Bot <phg@phi-gamma.net> | 2020-07-02 17:28:32 +0200 |
commit | 12fd8a1b4fa2a1cec2c363284f9baa572dbc96b9 (patch) | |
tree | b81423d0411502ba0216b773ebc1754b871fc1e3 /doc | |
parent | 74abcdb3fc2356cd40aa94d002f2a19aac549b40 (diff) | |
download | context-12fd8a1b4fa2a1cec2c363284f9baa572dbc96b9.tar.gz |
2020-07-02 16:06:00
Diffstat (limited to 'doc')
-rw-r--r-- | doc/context/documents/general/manuals/evenmore.pdf | bin | 1607905 -> 1633517 bytes | |||
-rw-r--r-- | doc/context/documents/general/manuals/luametatex.pdf | bin | 1232874 -> 1233125 bytes | |||
-rw-r--r-- | doc/context/sources/general/manuals/evenmore/evenmore-parameters.tex | 449 | ||||
-rw-r--r-- | doc/context/sources/general/manuals/evenmore/evenmore.tex | 3 |
4 files changed, 450 insertions, 2 deletions
diff --git a/doc/context/documents/general/manuals/evenmore.pdf b/doc/context/documents/general/manuals/evenmore.pdf Binary files differindex 0f7da622e..102323f06 100644 --- a/doc/context/documents/general/manuals/evenmore.pdf +++ b/doc/context/documents/general/manuals/evenmore.pdf diff --git a/doc/context/documents/general/manuals/luametatex.pdf b/doc/context/documents/general/manuals/luametatex.pdf Binary files differindex db9b643ad..8741c2c0d 100644 --- a/doc/context/documents/general/manuals/luametatex.pdf +++ b/doc/context/documents/general/manuals/luametatex.pdf diff --git a/doc/context/sources/general/manuals/evenmore/evenmore-parameters.tex b/doc/context/sources/general/manuals/evenmore/evenmore-parameters.tex new file mode 100644 index 000000000..b07378fae --- /dev/null +++ b/doc/context/sources/general/manuals/evenmore/evenmore-parameters.tex @@ -0,0 +1,449 @@ +% language=us + +% This feature was done mid May 2020 with Alien Chatter (I really need to find the +% original cd's) in the background. + +\environment evenmore-style + +\startcomponent evenmore-parameters + +\startchapter[title=Parameters] + +When \TEX\ reads input it either does something directly, like setting a +register, loading a font, turning a character into a glyph node, packaging a box, +or it sort of collects tokens and stores them somehow, in a macro (definition), +in a token register, or someplace temporary to inject them into the input later. +Here we'll be discussing macros, which have a special token list containing the +preamble defining the arguments and a body doing the real work. For instance when +you say: + +\starttyping[option=TEX] +\def\foo#1#2{#1 + #2 + #1 + #2} +\stoptyping + +the macro \type {\foo} is stored in such a way that it knows how to pick up the +two arguments and when expanding the body, it will inject the collected arguments +each time a reference like \type {#1} or \type {#2} is seen. In fact, quite +often, \TEX\ pushes a list of tokens (like an argument) in the input stream and +then detours in taking tokens from that list. Because \TEX\ does all its memory +management itself the price of all that copying is not that high, although during +a long and more complex run the individual tokens that make the forward linked +list of tokens get scattered in token memory and memory access is still the +bottleneck in processing. + +A somewhat simplified view of how a macro like this gets stored is the following: + +\starttyping +hash entry "foo" with property "macro call" => + + match (# property stored) + match (# property stored) + end of match + + match reference 1 + other character + + match reference 2 + other character + + match reference 1 + other character + + match reference 2 +\stoptyping + +When a macro gets expanded, the scanner first collects all the passed arguments +and then pushes those (in this case two) token lists on the parameter stack. Keep +in mind that due to nesting many kinds of stacks play a role. When the body gets +expanded and a reference is seen, the argument that it refers to gets injected +into the input, so imagine that we have this definition: + +\starttyping[option=TEX] +\foo#1#2{\ifdim\dimen0=0pt #1\else #2\fi} +\stoptyping + +and we say: + +\starttyping[option=TEX] +\foo{yes}{no} +\stoptyping + +then it's as if we had typed: + +\starttyping[option=TEX] +\ifdim\dimen0=0pt yes\else no\fi +\stoptyping + +So, you'd better not have something in the arguments that messes up the condition +parser! From the perspective of an expansion machine it all makes sense. But it +also means that when arguments are not used, they still get parsed and stored. +Imagine using this one: + +\starttyping[option=TEX] +\def\foo#1{\iffalse#1\oof#1\oof#1\oof#1\oof#1\fi} +\stoptyping + +When \TEX\ sees that the condition is false it will enter a fast scanning mode +where it only looks at condition related tokens, so even if \type {\oof} is not +defined this will work ok: + +\starttyping[option=TEX] +\foo{!} +\stoptyping + +But when we say this: + +\starttyping[option=TEX] +\foo{\else} +\stoptyping + +It will bark! This is because each \type {#1} reference will be resolved, so we +effectively have + +\starttyping[option=TEX] +\def\foo#1{\iffalse\else\oof\else\oof\else\oof\else\oof\else\fi} +\stoptyping + +which is not good. On the other hand, since expansion takes place in quick +parsing mode, this will work: + +\starttyping[option=TEX] +\def\oof{\else} +\foo\oof +\stoptyping + +which actually is: + +\starttyping[option=TEX] +\def\foo#1{\iffalse\oof\oof\oof\oof\oof\oof\oof\oof\oof\fi} +\stoptyping + +So, a reference to an argument effectively is just a replacement. As long as you +keep that in mind, and realize that while \TEX\ is skipping \quote {if} branches +nothing gets expanded, you're okay. + +Most users will associate the \type {#} character with macro arguments or +preambles in low level alignments, but since most macro packages provide a higher +level set of table macros the latter is less well known. But, as often with +characters in \TEX, you can do magic things: + +\starttyping[option=TEX] +\catcode`?=\catcode`# + +\def\foo #1#2?3{?1?2?3} \meaning\foo\space=>\foo{1}{2}{3}\par +\def\foo ?1#2?3{?1?2?3} \meaning\foo\space=>\foo{1}{2}{3}\par +\def\foo ?1?2#3{?1?2?3} \meaning\foo\space=>\foo{1}{2}{3}\par +\stoptyping + +Here the question mark also indicates a macro argument. However, when expanded +we see this as result: + +\starttyping +macro:#1#2?3->?1?2?3 =>123 +macro:?1#2?3->?1?2?3 =>123 +macro:?1?2#3->#1#2#3 =>123 +\stoptyping + +The last used argument signal character (officially called a match character, +here we have two that fit that category, \type {#} and \type {?}) is used in the +serialization! Now, there is an interesting aspect here. When \TEX\ stores the +preamble, as in our first example: + +\starttyping + match (# property stored) + match (# property stored) + end of match +\stoptyping + +the property is stored, so in the later example we get: + +\starttyping + match (# property stored) + match (# property stored) + match (? property stored) + end of match +\stoptyping + +But in the macro body the number is stored instead, because we need it as +reference to the parameter, so when that bit gets serialized \TEX\ (or more +accurately: \LUATEX, which is what we're using here) doesn't know what specific +signal was used. When the preamble is serialized it does keep track of the last +so|-|called match character. This is why we see this inconsistency in rendering. + +A simple solution would be to store the used signal for the match argument, which +probably only takes a few lines of extra code (using a nine integer array instead +of a single integer), and use that instead. I'm willing to see that as a bug in +\LUATEX\ but when I ran into it I was playing with something else: adding the +ability to prevent storing unused arguments. But the resulting confusion can make +one wonder why we do not always serialize the match character as \type {#}. + +It was then that I noticed that the preamble stored the match tokens and not the +number and that \TEX\ in fact assumes that no mixture is used. And, after +prototyping that in itself trivial change I decided that in order to properly +serialize this new feature it also made sense to always serialize the match token +as \type {#}. I simply prefer consistency over confusion and so I caught two +flies in one stroke. The new feature is indicated with a \type {#0} parameter: + +\startbuffer + +\bgroup +\catcode`?=\catcode`# + +\def\foo ?1?0?3{?1?2?3} \meaning\foo\space=>\foo{1}{2}{3}\crlf +\def\foo ?1#0?3{?1?2?3} \meaning\foo\space=>\foo{1}{2}{3}\crlf +\def\foo #1#2?3{?1?2?3} \meaning\foo\space=>\foo{1}{2}{3}\crlf +\def\foo ?1#2?3{?1?2?3} \meaning\foo\space=>\foo{1}{2}{3}\crlf +\def\foo ?1?2#3{?1?2?3} \meaning\foo\space=>\foo{1}{2}{3}\crlf +\egroup +\stopbuffer + +\typebuffer[option=TEX] + +\start +\getbuffer +\stop + +So, what is the rationale behind this new \type{#0} variant? Quite often you +don't want to do something with an argument at all. This happens when a macro +acts upon for instance a first argument and then expands another macro that +follows up but only deals with one of many arguments and discards the rest. Then +it makes no sense to store unused arguments. Keep in mind that in order to use it +more than once an argument does need to be stored, because the parser only looks +forward. In principle there could be some optimization in case the tokens come +from macros but we leave that for now. So, when we don't need an argument, we can +avoid storing it and just skip over it. Consider the following: + +\startbuffer +\def\foo #1{\ifnum#1=1 \expandafter\fooone\else\expandafter\footwo\fi} +\def\fooone#1#0{#1} +\def\footwo#0#2{#2} +\foo{1}{yes}{no} +\foo{0}{yes}{no} +\stopbuffer + +\typebuffer[option=TEX] + +We get: + +\getbuffer + +Just for the record, tracing of a macro shows that indeed there is no argument +stored: + +\starttyping[option=TEX] +\def\foo#1#0#3{....} +\foo{11}{22}{33} +\foo #1#0#3->.... +#1<-11 +#2<- +#3<-33 +\stoptyping + +Now, you can argue, what is the benefit of not storing tokens? As mentioned +above, the \TEX\ engines do their own memory management. \footnote {An added +benefit is that dumping and undumping is relatively efficient too.} This has +large benefits in performance especially when one keeps in mind that tokens get +allocated and are recycled constantly (take only lookahead and push back). + +However, even if this means that storing a couple of unused arguments doesn't put +much of a dent in performance, it does mean that a token sits somewhere in memory +and that this bit of memory needs to get accessed. Again, this is no big deal on +a computer where a \TEX\ job can take one core and basically is the only process +fighting for \CPU\ cache usage. But less memory access might be more relevant in +a scenario of multiple virtual machines running on the same hardware or multiple +\TEX\ processes on one machine. I didn't carefully measure that so I might be +wrong here. Anyway, it's always good to avoid moving around data when there is no +need for it. + +Just to temper expectations with respect to performance, here are some examples: + +\starttyping[option=TEX] +\catcode`!=9 % ignore this character +\firstoftwoarguments + {!!!!!!!!!!!!!!!!!!!}{!!!!!!!!!!!!!!!!!!!} +\secondoftwoarguments + {!!!!!!!!!!!!!!!!!!!}{!!!!!!!!!!!!!!!!!!!} +\secondoffourarguments + {!!!!!!!!!!!!!!!!!!!}{!!!!!!!!!!!!!!!!!!!} + {!!!!!!!!!!!!!!!!!!!}{!!!!!!!!!!!!!!!!!!!} +\stoptyping + +In \CONTEXT\ we define these macros as follows: + +\starttyping[option=TEX] +\def\firstoftwoarguments #1#2{#1} +\def\secondoftwoarguments #1#2{#2} +\def\secondoffourarguments#1#2#3#4{#2} +\stoptyping + +The performance of 2 million expansions is the following (probably half or less +on a more modern machine): + +\starttabulate[||||] +\BC macro \BC total \BC step \NC \NR +\NC \type {\firstoftwoarguments} \NC 0.245 \NC 0.000000123 \NC \NR +\NC \type {\secondoftwoarguments} \NC 0.251 \NC 0.000000126 \NC \NR +\NC \type {\secondoffourarguments} \NC 0.390 \NC 0.000000195 \NC \NR +\stoptabulate + +But we could use this instead: + +\starttyping[option=TEX] +\def\firstoftwoarguments #1#0{#1} +\def\secondoftwoarguments #0#2{#2} +\def\secondoffourarguments#0#2#0#0{#2} +\stoptyping + +which gives: + +\starttabulate[||||] +\BC macro \BC total \BC step \NC \NR +\NC \type {\firstoftwoarguments} \NC 0.229 \NC 0.000000115 \NC \NR +\NC \type {\secondoftwoarguments} \NC 0.236 \NC 0.000000118 \NC \NR +\NC \type {\secondoffourarguments} \NC 0.323 \NC 0.000000162 \NC \NR +\stoptabulate + +So, no impressive differences, especially when one considers that when that many +expansions happen in a run, getting the document itself rendered plus expanding +real arguments (not something defined to be ignored) will take way more time +compared to this. I always test an extension like this on the test suite +\footnote {Currently some 1600 files that take 24 minutes plus or minus 30 +seconds to process on a high end 2013 laptop. The 260 page manual with lots of +tables, verbatim and \METAPOST\ images takes around 11 seconds. A few +milliseconds more or less don't really show here. I only time these runs because +I want to make sure that there are no dramatic consequences.} as well as the +\LUAMETATEX\ manual (which takes about 11 seconds) and although one can notice a +little gain, it makes more sense not to play music on the same machine as we run +the \TEX\ job, if gaining milliseconds is that important. But, as said, it's more +about unnecessary memory access than about \CPU\ cycles. + +This extension is downward compatible and its overhead can be neglected. Okay, +the serialization now always uses \type {#} but it was inconsistent before, so +I'm willing to sacrifice that (and I'm pretty sure no \CONTEXT\ user cares or +will even notice). Also, it's only in \LUAMETATEX\ (for now) so that other macro +packages don't suffer from this patch. The few cases where \CONTEXT\ can benefit +from it are easy to isolate for \MKIV\ and \LMTX\ so we can support \LUATEX\ and +\LUAMETATEX. + +I mentioned \LUATEX\ and how it serializes, but for the record, let's see how +\PDFTEX, which is very close to original \TEX\ in terms of source code, does it. +If we have this input: + +\starttyping[option=TEX] +\catcode`D=\catcode`# +\catcode`O=\catcode`# +\catcode`N=\catcode`# +\catcode`-=\catcode`# +\catcode`K=\catcode`# +\catcode`N=\catcode`# +\catcode`U=\catcode`# +\catcode`T=\catcode`# +\catcode`H=\catcode`# + +\def\dek D1O2N3-4K5N6U7T8H9{#1#2#3 #4#6#7#8#9} + +{\meaning\dek \tracingall \dek don{}knuth} +\stoptyping + +The meaning gets typeset as: + +\starttyping +macro:D1O2N3-4K5N6U7T8H9->H1H2H3 H4H6H7H8H9don nuth +\stoptyping + +while the tracing reports: + +\starttyping +\dek D1O2N3-4K5N6U7T8H9->H1H2H3 H5H6H7H8H9 +D1<-d +O2<-o +N3<-n +-4<- +K5<-k +N6<-n +U7<-u +T8<-t +H9<-h +\stoptyping + +The reason for the difference, as mentioned, is that the tracing uses the +template and therefore uses the stored match token, while the meaning uses the +reference match tokens that carry the number and at that time has no access to +the original match token. Keeping track of that for the sake of tracing would not +make sense anyway. So, traditional \TEX, which is what \PDFTEX\ is very close to, +uses the last used match token, the \type {H}. Maybe this example can convince +you that dropping that bit of log related compatibility is not that much of a +problem. I just tell myself that I turned an unwanted side effect into a new +feature. + +\subject{A few side notes} + +The fact that characters can be given a special meaning is one of the charming +properties of \TEX. Take these two cases: + +\starttyping[option=TEX] +\bgroup\catcode`\&=5 &\egroup +\bgroup\catcode`\!=5 !\egroup +\stoptyping + +In both lines there is now an alignment character used outside an alignment. And, +in both cases the error message is similar: + +\starttyping +! Misplaced alignment tab character & +! Misplaced alignment tab character ! +\stoptyping + +So, indeed the right character is shown in the message. But, as soon as you ask +for help, there is a difference: in the first case the help is specific for a tab +character, but in the second case a more generic explanation is given. Just try +it. + +The reason is an explicit check for the ampersand being used as tab character. +Such is the charm of \TEX. I'll probably opt for a trivial change to be +consistent here, although in \CONTEXT\ the ampersand is just an ampersand so no +user will notice. + +There are a few more places where, although in principle any character can serve +any purpose, there are hard coded assumptions, like \type {$} being used for +math, so a missing dollar is reported, even if math started with another +character being used to enter math mode. This makes sense because there is no +urgent need to keep track of what specific character was used for entering math +mode. An even stronger argument could be that \TEX ies expect dollars to be used +for that purpose. Of course this works fine: + +\starttyping[option=TEX] +\catcode`€=\catcode`$ +€ \sqrt{x^3} € +\stoptyping + +But when we forget an \type {€} we get messages like: + +\starttyping +! Missing $ inserted +\stoptyping + +or more generic: + +\starttyping +! Extra }, or forgotten $ +\stoptyping + +which is definitely a confirmation of \quotation {America first}. Of course we +can compromise in display math because this is quite okay: + +\starttyping[option=TEX] +\catcode`€=\catcode`$ +$€ \sqrt{x^3} €$ +\stoptyping + +unless of course we forget the last dollar in which case we are told that + +\starttyping +! Display math should end with $$ +\stoptyping + +so no matter what, the dollar wins. Given how ugly the Euro sign looks I can live +with this, although I always wonder what character would have been taken if \TEX\ +was developed in another country. + +\stopchapter + +\stopcomponent diff --git a/doc/context/sources/general/manuals/evenmore/evenmore.tex b/doc/context/sources/general/manuals/evenmore/evenmore.tex index c2e4e232b..357fb9f24 100644 --- a/doc/context/sources/general/manuals/evenmore/evenmore.tex +++ b/doc/context/sources/general/manuals/evenmore/evenmore.tex @@ -21,8 +21,7 @@ \component evenmore-libraries \component evenmore-whattex \component evenmore-numbers - % \component evenmore-parameters - \startchapter[title=Parameters] {\em This will appear first in \TUGBOAT.} \stopchapter + \component evenmore-parameters \component evenmore-parsing \component evenmore-tokens \stopbodymatter |