.TH "md_src_plugins_mathcheck_README" 3elektra "Sun May 29 2016" "Version 0.8.14" "Elektra" \" -*- nroff -*-
.ad l
.nh
.SH NAME
md_src_plugins_mathcheck_README \- README 

.IP "\(bu" 2
infos = Information about the mathcheck plugin is in keys below
.IP "\(bu" 2
infos/author = Thomas Waser thomas.waser@libelektra.org
.IP "\(bu" 2
infos/licence = BSD
.IP "\(bu" 2
infos/needs =
.IP "\(bu" 2
infos/provides = check
.IP "\(bu" 2
infos/placements = presetstorage
.IP "\(bu" 2
infos/description =
.PP
.PP
Compares a key value to a mathematical expression using polish prefix notation defined in the \fCcheck/math\fP metakey\&. Operations are \fC+ - / *\fP \&. Operants are keys with names relative to the parent key\&. How the values are compared is specified at the beginning of the metakey using the conditions \fC<, <=, ==, !=, =>, >, :=\fP \fC:=\fP is used to set key values\&. All values are interpreted as \fCdouble\fP floating point values\&.
.PP
.SS "Examples"
.PP
\fCcheck/math = '== + testval1 + testval2 testval3'\fP compares the keyvalue to the sum of testval1-3 and yields an error if the values are not equal\&. \fCcheck/math = '\\<= - testval1 * testval2 testval3'\fP tests if the keyvalue is less than or equal to testval1 - (testval2 * testval3) and yields an error if not\&.
.PP
Full example: 
.PP
.nf
    kdb mount mathcheck.dump /example/mathcheck dump mathcheck
    kdb set user/example/mathcheck/a 3.1
    kdb set user/example/mathcheck/b 4.5
    kdb set user/example/mathcheck/k 7.6
    kdb setmeta user/example/mathcheck/k check/math "== + a b"
    kdb set user/example/mathcheck/k 7.7   # fails

.fi
.PP
.PP
To calculate values on-demand you can use: 
.PP
.nf
    kdb setmeta user/example/mathcheck/k check/math ":= + a b"
    kdb get user/example/mathcheck/k       # 12.5
    kdb set user/example/mathcheck/a 5.5
    kdb get user/example/mathcheck/k       # 10

.fi
.PP
.PP
It also works with constants: 
.PP
.nf
    kdb setmeta user/example/mathcheck/k check/math ":= + a '5'"
    kdb get user/example/mathcheck/k       # 10.5
    kdb set user/example/mathcheck/a 8.0
    kdb get user/example/mathcheck/k       # 13
.fi
.PP