1Math::Expression::EvaluUasteorr(C3o)ntributed Perl DocumMeanttha:t:iEoxnpression::Evaluator(3)
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NAME

6       Math::Expression::Evaluator - parses, compiles and evaluates mathematic
7       expressions
8

SYNOPSIS

10           use Math::Expression::Evaluator;
11           my $m = Math::Expression::Evaluator->new;
12
13           print $m->parse("a = 12; a*3")->val(), "\n";
14           # prints 36
15           print $m->parse("2^(a/3)")->val(), "\n";
16           # prints 8 (ie 2**3)
17           print $m->parse("a / b")->val({ b => 6 }), "\n";
18           # prints 36
19           print $m->parse("log2(16)")->val(), "\n";
20           # prints 4
21
22           # if you care about speed
23           my $func = $m->parse('2 + (4 * b)')->compiled;
24           for (0 .. 100){
25               print $func->({b => $_}), "\n";
26           }
27

DESCRIPTION

29       Math::Expression::Evaluator is a parser, compiler and interpreter for
30       mathematical expressions. It can handle normal arithmetics (includings
31       powers wit "^" or "**"), builtin functions like sin() and variables.
32
33       Multiplication "*", division "/" and modulo "%" have the same
34       precedence, and are evaluated left to right. The modulo operation
35       follows the standard perl semantics, that is is the arguments are
36       castet to integer before preforming the modulo operation.
37
38       Multiple exressions can be seperated by whitespaces or by semicolons
39       ';'.  In case of multiple expressions the value of the last expression
40       is returned.
41
42       Variables can be assigned with a single '=' sign, their name has to
43       start with a alphabetic character or underscore "[a-zA-Z_]", and may
44       contain alphabetic characters, digits and underscores.
45
46       Values for variables can also be provided as a hash ref as a parameter
47       to val(). In case of collision the explicitly provided value is used:
48
49          $m->parse("a = 2; a")->val({a => 1});
50
51       will return 1, not 2.
52
53       The following builtin functions are supported atm:
54
55       ·   trignometric functions: sin, cos, tan
56
57       ·   inverse trigonomic functions: asin, acos, atan
58
59       ·   Square root: sqrt
60
61       ·   exponentials: exp, sinh, cosh
62
63       ·   logarithms: log, log2, log10
64
65       ·   constants: pi() (you need the parenthesis to distinguish it from
66           the variable pi)
67
68       ·   rounding: ceil(), floor()
69
70       ·   other: theta (theta(x) = 1 for x > 0, theta(x) = 0 for x < 0)
71

METHODS

73       new
74         generates a new MathExpr object. accepts an optional argument, a hash
75         ref that contains configurations. If this hash sets force_semicolon
76         to true, expressions have to be separated by a semicolon ';'.
77
78       parse
79         Takes a string as argument, and generates an Abstract Syntax
80         Tree(AST) that is stored internally.
81
82         Returns a reference to the object, so that method calls can be
83         chained:
84
85             print MathExpr->new->parse("1+2")->val;
86
87         Parse failures cause this method to die with a stack trace.
88
89         You can call "parse" on an existing Math::Expression::Evaluator
90         object to re-use it, in which case previously set variables and
91         callbacks persist between calls.
92
93         This (perhaps contrived) example explains this:
94
95             my $m = Math::Expression::Evaluator->new('a = 3; a');
96             $m->val();
97             $m->parse('a + 5');
98             print $m->val(), "\n"   # prints 8, because a = 3 was re-used
99
100         If that's not what you want, create a new object instead - the
101         constructor is rather cheap.
102
103       compiled
104         Returns an anonymous function that is a compiled version of the
105         current expression. It is much faster to execute than the other
106         methods, but its error messages aren't as informative (instead of
107         complaining about a non-existing variable it dies with "Use of
108         uninitialized value in...").
109
110         Note that variables are not persistent between calls to compiled
111         functions (and it wouldn't make sense anyway, because such a function
112         corresponds always to exactly one expression, not many as a MEE
113         object).
114
115         Variables that were stored at the time when "compiled()" is called
116         are availble in the compiled function, though.
117
118       val
119         Executes the AST generated by parse(), and returns the number that
120         the expression is evaluated to. It accepts an optional hash reference
121         that contain values for variables:
122
123             my $m = MathExpr->new;
124             $m->parse("(x - 1) / (x + 1)");
125             foreach (0 .. 10) {
126                 print $_, "\t", $m->val({x => $_}), "\n";
127             }
128
129       optimize
130         Optimizes the internal AST, so that subsequent calls to "val()" will
131         be a bit faster. See "Math::Expression::Evaluator::Optimizer" for
132         performance considerations and informations on the implemented
133         optimizations.
134
135         But note that a call to "optimize()" only pays off if you call
136         "val()" multiple times.
137
138       variables
139         "variables()" returns a list of variables that are used in the
140         expression.
141
142       set_var_callback
143         Allows you to set a callback which the Match::Expression::Evaluator
144         object calls when it can't find a variable. The name of the variable
145         is passed in as the first argument. If the callback function can't
146         handle that variable either, it should die, just like the default one
147         does.
148
149             my $m = Math::Expression::Evaluator->new();
150             $m->parse('1 + a');
151             my $callback = sub { ord($_[0]) };
152             $m->set_var_callback($callback);
153             print $m->val();    # calls $callback, which returns 97
154                                 # so $m->val() return 98
155
156         The callback will be called every time the variable is accessed, so
157         if it requires expensive calculations, you are encouraged to cache it
158         either yourself our automatically with Memoize.
159
160       set_function
161         Allows to add a user-defined function, or to override a built-in
162         function.
163
164             my $m = Math::Expression::Evaluator->new();
165             $m->set_function('abs', sub { abs($_[0]) });
166             $m->parse('abs(10.6)');
167             print $m->val();
168
169         If you first compile the expression to a perl closure and then call
170         "<$m-"set_function>> again, the compiled function stays unaffected,
171         so
172
173             $m->set_function('f', sub { 42 });
174             my $compiled = $m->parse('f')->compiled;
175             $m->set_function('f', sub { -23 });
176             print $compiled->();
177
178         print out 42, not "-23".
179
180       ast_size
181         "ast_size" returns an integer which gives a crude measure of the
182         logical size of the expression. Note that this value isn't
183         guarantueed to be stable across multiple versions of this module. It
184         is mainly intended for testing.
185

SPEED

187       MEE isn't as fast as perl, because it is built on top of perl.
188
189       If you execute an expression multiple times, it pays off to either
190       optimize it first, or (even better) compile it to a pure perl function.
191
192                          Rate  no_optimize     optimize opt_compiled     compiled
193           no_optimize  83.9/s           --         -44%         -82%         -83%
194           optimize      150/s          78%           --         -68%         -69%
195           opt_compiled  472/s         463%         215%           --          -4%
196           compiled      490/s         485%         227%           4%           --
197
198       This shows the time for 200 evaluations of "2+a+5+(3+4)" (with MEE
199       0.0.5).  As you can see, the non-optimized version is painfully slow,
200       optimization nearly doubles the execution speed. The compiled and the
201       optimized-and-then-compiled versions are both much faster.
202
203       With this example expression the optimization prior to compilation pays
204       off if you evaluate it more than 1000 times. But even if you call it
205       "10**5" times the optimized and compiled version is only 3% faster than
206       the directly compiled one (mostly due to perl's overhead for method
207       calls).
208
209       So to summarize you should compile your expresions, and if you have
210       really many iterations it might pay off to optimize it first (or to
211       write your program in C instead ;-).
212

BUGS AND LIMITATIONS

214       ·   Modulo operator produces an unnecessary big AST, making it
215           relatively slow
216

INTERNALS

218       The AST can be accessed as "$obj-"{ast}>. Its structure is described in
219       Math::Expression::Evaluator::Parser (or you can use Data::Dumper to
220       figure it out for yourself). Note that the exact form of the AST is
221       considered to be an implementation detail, and subject to change.
222

SEE ALSO

224       Math::Expression also evaluates mathematical expressions, but also
225       handles string operations.
226
227       If you want to do symbolic (aka algebraic) transformations,
228       Math::Symbolic will fit your needs.
229

LICENSE

231       This module is free software. You may use, redistribute and modify it
232       under the same terms as perl itself.
233
235       Copyright (C) 2007 - 2009 Moritz Lenz, <http://perlgeek.de/>,
236       moritz@faui2k3.org
237

DEVELOPMENT

239       You can obtain the latest development version from github
240       <http://github.com/moritz/math-expression-evaluator>.
241
242           git clone git://github.com/moritz/math-expression-evaluator.git
243
244       If you want to contribute something to this module, please ask me for a
245       commit bit to the github repository, I'm giving them out freely.
246

ACKNOWLEDGEMENTS

248       The following people have contributed to this module, in no particular
249       order:
250
251       Leonardo Herrera
252           Initial patch for "set_function"
253
254       Tina Müller
255           Helpful feedback
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259perl v5.32.0                      2020-07-28    Math::Expression::Evaluator(3)
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