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Some folks might think: “you still use RCS”?!? And we will say, hey, at least we switched from SCCS to RCS back in … I think it was around 1994 ... at least we are keeping up! :-) :-) :-) Logs say that SCCS version 18 became RCS version 19 on 1994 March 18. RCS served us well. But now it is time to move on. And so we are switching to git. Calc releases produce a lot of file changes. In the 125 releases of calc since 1996, when I started managing calc releases, there have been 15473 file mods!
98 lines
3.1 KiB
Plaintext
98 lines
3.1 KiB
Plaintext
NAME
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null - null value
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SYNOPSIS
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null([v_1, v_2,...])
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TYPES
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v_1, v_2,... any
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return null
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DESCRIPTION
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After evaluating in order any arguments it may have, null(...)
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returns the null value. This is a particular value, different from
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all other types; it is the only value v for which isnull(v) returns
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TRUE. The null value tests as FALSE in conditions, and normally
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delivers no output in print statements, except that when a list or
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matrix is printed, null elements are printed as "NULL".
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A few builtin functions may return the null value, e.g.
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printf(...) returns the null value; if L = list(), then both
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pop(L) and remove(L) return the null value; when successful,
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file-handling functions like fclose(fs), fflush(fs), fputs(fs, ...)
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return the null value when successful (when they fail they return an
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error-value). User-defined functions where execution ends
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without a "return" statement or with "return ;" return the null
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value.
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Missing expressions in argument lists are assigned the null value.
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For example, after
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define f(a,b,c) = ...
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calling
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f(1,2)
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is as if c == null(). Similarly, f(1,,2) is as if b == null().
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(Note that this does not occur in initialization lists; missing
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expressions there indicate no change.)
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The null value may be used as an argument in some operations, e.g.
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if v == null(), then for any x, x + v returns x.
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When calc is used interactively, a function that returns the null value
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causes no printed output and does not change the "oldvalue". Thus,
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null(config("mode", "frac")) may be used to change the output mode
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without printing the current mode or changing the stored oldvalue.
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EXAMPLE
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; L = list(-1,0,1,2);
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; while (!isnull(x = pop(L)) print x,; print
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-1 0 1 2
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; printf("%d %d %d\n", 2, , 3);
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2 3
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; L = list(,1,,2,)
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; print L
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list (5 elements, 5 nonzero):
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[[0]] = NULL
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[[1]] = 1
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[[2]] = NULL
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[[3]] = 2
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[[4]] = NULL
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; a = 27
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; null(pi = pi(1e-1000))
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; .
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27
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LIMITS
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The number of arguments is not to exceed 1024.
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LINK LIBRARY
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none
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SEE ALSO
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isnull, test
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## Copyright (C) 1999-2006 Landon Curt Noll
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##
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## Calc is open software; you can redistribute it and/or modify it under
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## the terms of the version 2.1 of the GNU Lesser General Public License
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## as published by the Free Software Foundation.
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##
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## Calc is distributed in the hope that it will be useful, but WITHOUT
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## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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## or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
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## Public License for more details.
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##
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## A copy of version 2.1 of the GNU Lesser General Public License is
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## distributed with calc under the filename COPYING-LGPL. You should have
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## received a copy with calc; if not, write to Free Software Foundation, Inc.
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## 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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##
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## Under source code control: 1996/03/12 23:10:01
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## File existed as early as: 1996
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##
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## chongo <was here> /\oo/\ http://www.isthe.com/chongo/
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## Share and enjoy! :-) http://www.isthe.com/chongo/tech/comp/calc/
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