NAME
Math::Expression::Evaluator - parses and evaluates mathematic
expressions
SYNOPSIS
use Math::Expression::Evaluator;
my $m = new Math::Expression::Evaluator;
print $m->parse("a = 12; a*3")->val(), "\n";
# prints 36
print $m->parse("2^(a/3)")->val(), "\n";
# prints 8 (ie 2**3)
print $m->parse("a / b")->val({ b => 6 }), "\n";
# prints 36
print $m->parse("log2(16)")->val(), "\n";
# prints 4
DESCRIPTION
Math::Expression::Evaluator is a simple, recursive descending parser for
mathematical expressions. It can handle normal arithmetics (includings
powers ^), builtin functions like sin() and variables.
Multiple exressions can be seperated by whitespaces or by semicolons
';'. In case of multiple expressions the value of the last expression is
returned.
Variables can be assigned with a single '=' sign, their name has to
start with a alphabetic character or underscore "[a-zA-Z_]", and may
contain alphabetic characters, digits and underscores.
Values for variables can also be provided as a hash ref as a parameter
to val(). In case of collision the explicitly provided value is used:
$m->parse("a = 2; a")->val({a => 1});
will return 1, not 2.
The following builtin functions are supported atm:
* trignometric functions: sin, cos, tan
* inverse trigonomic functions: asin, acos, atan
* Square root: sqrt
* exponentials: exp, sinh, cosh
* logarithms: log, log2, log10
* constants: pi() (you need the parenthesis to distinguish it from the
variable pi)
* other: theta (theta(x) = 1 for x > 0, theta(x) = 0 for x < 0)
METHODS
new
generates a new MathExpr object. accepts an optional argument, a hash
ref that contains configurations. If this hash sets force_semicolon to
true, expressions have to be separated by a semicolon ';'.
parse
Takes a string as argument, and generates an AST that is stored
internally.
Returns a reference to the object, so that method calls can be
chained:
print MathExpr->new->parse("1+2")->val;
Parse failures cause this method to die with a stack trace.
val
Executes the AST generated by parse(), and returns the number that the
expression is evaluated to. It accepts an optional hash reference that
contain values for variables:
my $m = new MathExpr;
$m->parse("(x - 1) / (x + 1)");
foreach (0 .. 10) {
print $_, "\t", $m->val({x => $_}), "\n";
}
optimize
Optimizes the AST generated by parse(), that is evaluates any
subexpression that only depends on numerical constants, e.g.
a + 3 * 4
becomes
a + 12
Please note that the optimization by itself is rather costly compared
to the evaluation by "val()", so only do this if you plan to evaluate
the expression multiple times, and be sure to benchmark it to know if
you do the right thing.
If you don't know how the expression looks like (e.g. user supplied
input) you should call optimize() if you evaluate the expression at
least 20 times.
LICENSE
This module is free software. You may use, redistribute and modify it
under the same terms as perl itself.
AUTHOR
Moritz Lenz, , moritz@faui2k3.org
DEVELOPMENT
You can obtain the latest development version via subversion:
svn co https://casella.verplant.org/svn/moritz/cpan/Math-Expression-Evaluator/