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Add LIBDOC; DPRINT ALAN -- documentation for DPRINT package.

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Resolves #1057.
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Eric Swenson
2018-07-13 12:09:36 -07:00
parent 3080ca8796
commit db5208548f
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doc/libdoc/dprint.alan Executable file
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-*-Text-*-
DPRINT is Alan's private hack for making defstructs print out nicely in
MacLisp. Unlike defstruct itself, DPRINT can be used in ways that are
incompatible with several other pieces of "semi-standard" MacLisp software,
notably the NIL-in-MacLisp STRING package and the NIL-in-MacLisp CLASS
system.
DPRINT also defines a simple MacLisp INSPECT function, and a DESCRIBE
function. These can be safely used with anything else you might care to
load. No documentation is provided for either of these functions. To see
how DESCRIBE works, just apply it to a few things. To see how INSPECT
works, apply it to something and then type "?" to the prompt. One
non-obvious feature is that both functions, when applied to no arguments
will use the value of * as their argument.
Because you might only want the DESCRIBE and INSPECT functions, just
loading DPRINT will not turn on any incompatibilities with any other
(known) MacLisp software package. However if you want to be able to
control the printing of hunks you can take the plunge and turn DPRINT on.
To do this use the DPRINT function which takes one argument. If that
argument is NIL then printing of hunks is reverted to the system default.
If that argument is non-NIL then smart hunk printing is turned on.
Smart hunk printing does three things for you.
1. Basic hunks print between square brackets rather than as funny-looking
conses. They also print with the CXR 0 element first. So where you used
to see "(BAR . BAZ . FOO .)" you now see "[FOO BAR BAZ]". This syntax will
NOT read back in again. If you really want to READ hunks, stop reading
now.
2. "Named" hunks produced by defstruct will not print as above but will
print like "#SPACESHIP-72654", where "SPACESHIP" is the name of the
defstruct and 72654 is a unique octal number (actually the address of the
structure in memory).
3. Named hunks produced by defstructs that used the :PRINT defstruct
option to specify a printed representation will print as specified. See
the defstruct documentation for more on that. (<LIBLSP>STRUCT.NEWS
contains the relevant update.)
Two things to be aware of.
1. In order to gain control of the printing of hunks, I have to grab
control of a resource that the NIL-in-MacLisp packages also attempt to
control. If I detect that they have already grabbed that resource, then
the DPRINT function will error. You may FORCE control of that resource by
saying (DPRINT 'SCREW). This will no doubt do unpredictable things to the
NIL-in-MacLisp crocks. Use it when you don't care about that.
2. in order to control printing I have to be prepared to handle at lot of
other nonsense about hunks. Specifically I have been fored to make the
following decisions:
Hunks will always self-evaluate. They have to do something because loading
a LEDIT on 20X requires that a single hunk be evaluated. (God knows why.)
EQUAL will always compare two hunks using EQ.
If some other operation is attempted on hunks that I don't find useful, you
will get the error message:
;(<hunk> <message> . <args>) -- Unknown message to hunk.
You can send me a complaint explaining just what it is that you think hunks
should do in this situation and we can negotiate it.