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Diffstat (limited to 'doc/context/sources/general/manuals/lowlevel/lowlevel-macros.tex')
| -rw-r--r-- | doc/context/sources/general/manuals/lowlevel/lowlevel-macros.tex | 32 |
1 files changed, 27 insertions, 5 deletions
diff --git a/doc/context/sources/general/manuals/lowlevel/lowlevel-macros.tex b/doc/context/sources/general/manuals/lowlevel/lowlevel-macros.tex index ef527732b..033bdee80 100644 --- a/doc/context/sources/general/manuals/lowlevel/lowlevel-macros.tex +++ b/doc/context/sources/general/manuals/lowlevel/lowlevel-macros.tex @@ -14,7 +14,6 @@ % \permanent\tolerant\protected\def\xx[#1]#*#;[#2]#:#3% loops .. todo - \usemodule[system-tokens] \environment lowlevel-style @@ -540,9 +539,30 @@ a use for \type {#<} and \type {#>}. A summary of all this is given here: \NC * \NC ignore spaces \NC \NR \NC : \NC pick up scanning here \NC \NR \NC ; \NC quit scanning \NC \NR +\ML +\NC . \NC ignore pars and spaces \NC \NR +\NC , \NC push back space when quit \NC \NR \LL \stoptabulate +The last two have not been discussed and were added later. The period +directive gobbles space and par tokens and discards them in the +process. The comma directive is like \type {*} but it pushes back a space +when the matching quits. + +\startbuffer +\tolerant\def\FooA[#1]#*[#2]{(#1/#2)} % remove spaces +\tolerant\def\FooB[#1]#,[#2]{(#1/#2)} % push back space + +/\FooA/ /\FooA / /\FooA[1]/ /\FooA[!] / /\FooA[1] [2]/ /\FooA[1] [2] /\par +/\FooB/ /\FooB / /\FooB[1]/ /\FooB[!] / /\FooB[1] [2]/ /\FooB[1] [2] /\par +\stopbuffer + +\typebuffer[example][option=TEX] \startpacked \getbuffer[example] \stoppacked + +Gobbling spaces versus pushing back is an interface design decision because it +has to do with consistency. + \stopsection \startsection[title=Runaway arguments] @@ -639,6 +659,8 @@ macro is a special version of the online variant: That one is always available and shows a similar list on the console. Again, users normally don't want to know such details. +\stopsection + \startsection[title=nesting] You can nest macros, as in: @@ -812,10 +834,10 @@ these can easily be fixed. So, it will be used but it will take a while to adapt the code base. One problem with frozen macros is that they don't play nice with for instance -\type {\futurelet}. Also, there are places in \CONTEXT\ where we actually do +\typ {\futurelet}. Also, there are places in \CONTEXT\ where we actually do redefine some core macro that we also want to protect from redefinition by a -user. One can of course \type {\unletfrozen} such a command first but as a bonus -we have a prefix \type {\overloaded} that can be used as prefix. So, one can easily +user. One can of course \typ {\unletfrozen} such a command first but as a bonus +we have a prefix \typ {\overloaded} that can be used as prefix. So, one can easily redefine a frozen macro but it takes a little effort. After all, this feature is mainly meant to protect a user for side effects of definitions, and not as final blocker. \footnote {As usual adding features like this takes some experimenting @@ -824,7 +846,7 @@ The fact that we can apply such features in large macro package like \CONTEXT\ helps figuring out the needs and best approaches.} A frozen macro can still be overloaded, so what if we want to prevent that? For -this we have the \type {\permanent} prefix. Internally we also create primitives +this we have the \typ {\permanent} prefix. Internally we also create primitives but we don't have a prefix for that. But we do have one for a very special case which we demonstrate with an example: |