The London Perl and Raku Workshop takes place on 26th Oct 2024. If your company depends on Perl, please consider sponsoring and/or attending.
 / 
Math-Formula-0.16
River stage zero No dependents
/ Math::Formula

NAME

Math::Formula - expressions on steroids

SYNOPSIS

  my $formula = Math::Formula->new('size', '42k + 324', %options);
  my $formula = Math::Formula->new(π => 3.14);
  my $size    = $formula->evaluate;

  # For a bit more complex formulas, you need a context object.
  my $context = Math::Formula::Context->new(name => 'example');
  $context->add( { size => '42k', header => '324', total => 'size + header' });
  my $total   = $context->value('total');

  # To build connectors to objects in your program, interfaces.
  # See Math::Formula::Context.
  my $formula = Math::Formula->new(size => \&own_sub, %options);

DESCRIPTION

WARNING: This is not a programming language: it lacks control structures, like loops and blocks. This module can be used to offer (very) flexible configuration (files) for users of your application. See Math::Formula::Context and Math::Formula::Config.

What makes Math::Formula special? Zillions of expression evaluators have been written in the past. The application where this module was written for, has special needs which were not served by them. This expression evaluator can do things which are usually hidden behind library calls.

Why do I need it? My application has many kinds of configurable rules, from different sources. Those rules often use times and durations in them, to organize processing activities. Each line in my configuration can now be a smart expression. Declarative programming.

Interested? Read more in the "DETAILS" section below.

METHODS

Constructors

Math::Formula->new($name, $expression, %options)

The expression needs a $name. Expressions can refer to each other via this name.

The $expression is usually a (utf8) string, which will get parsed and evaluated on demand. The $expression may also be a prepared node (any <Math::Formula::Type> object).

As special hook, you may also provide a CODE as $expression. This will be called as

  $expression->($context, $this_formula, %options);

Optimally, the expression returns any Math::Formula::Type object. Otherwise, auto-detection of the computed result kicks in. The %options are passed to evaluate() More details below in "CODE as expression" in Math::Formula::Context.

 -Option --Default
  returns  undef
returns => $type

Enforce that the type produced by the calculation of this $type. Otherwise, it may be different when other people are permitted to configure the formulas... people can make mistakes.

Accessors

$obj->expression()

Returns the expression, which was given at creation. Hence, it can be a string to be evaluated, a type-object, or a CODE reference.

$obj->name()

Returns the name of this expression.

$obj->returns()

Set when the expression promises to produce a certain type.

$obj->tree($expression)

Returns the Abstract Syntax Tree of the $expression. Some of the types are only determined at the first run, for optimal laziness. Used for debugging purposes only.

Running

$obj->evaluate( [ $context, %options ] )

Calculate the value for this expression given the $context. The Context groups the expressions together so they can refer to each other. When the expression does not contain Names, than you may go without context.

 -Option--Default
  expect  <any ::Type>
expect => $type

When specified, the result will be of the expected $type or undef. This overrules new(returns). Without either, the result type depends on the evaluation of the expression.

$obj->toType($data)

Convert internal Perl data into a Math::Formula internal types. For most times, this guess cannot go wrong. In other cases a mistake is not problematic.

In a small number of cases, auto-detection may break: is 'true' a boolean or a string? Gladly, this types will be cast into a string when used as a string; a wrong guess without consequences. It is preferred that your CODE expressions return explicit types: for optimal safety and performance.

See "CODE as expression" in Math::Formula::Context for details.

DETAILS

This module handles formulas. Someone (your application user) gets more power in configuring its settings. Very simple example:

  # In a back-up script, configured in JSON
  "daily_backups"  : "/var/tmp/backups/daily",
  "weekly_backups" : "/var/tmp/backups/weekly",
  
  # With Math::Formula::Config::JSON
  "backup_dir"     : "/var/tmp/backups/",
  "daily_backups"  : "= backup_dir ~ 'daily'",
  "weekly_backups" : "= backup_dir ~ 'weekly'",

The more configuration your application needs, the more useful this module gets. Especially when you need to work with timestamps.

Data-types

Examples for all data-types which Math::Formula supports:

  true and false               # real booleans
  "abc"  'abc'                 # the usual strings, WARNING: read below
  7  89k  5Mibi                # integers with multiplier support
  =~ "c$"                      # regular expression matching
  like "*c"                    # pattern matching
  2023-02-18T01:28:12+0300     # date-times
  2023-02-18+0100              # dates
  01:18:12                     # times
  -0600                        # time-zone
  P2Y3DT2H                     # duration
  name                         # outcome of other expressions

And constructs

  (1 + 2) * -3                 # operations and parenthesis
  "abc".length                 # attributes
  #unit.owner                  # fragments (nested context, namespaces)

Warning: in your code, all these above are place between quotes. This makes it inconvenient to use strings, which are also usually between quotes. So: strings should stand-out from expressions. Use any of the following syntaxes:

  "\"string\""   '"string"'    "'$string'"   # $string with escaped quotes!
  \"string"       \'string'    \$string      # or, use a SCALAR reference

When you use a Math::Formula::Context (preferred), you can select your own solution via Math::Formula::Context::new(lead_expressions). It is possible to configure that all strings get the normal quotes, and expressions start with = (or any other leading string).

Your expressions can look like this:

  my_age   => '(#system.now.date - 1966-05-04).years',
  is_adult => 'my_age >= 18',

Expressions can refer to values computed by other expressions. Also, external objects can maintain libraries of formulas or produce compatible data.

Sets of formulas

Let's start with a large group of related formulas, and the types they produce:

  birthday: 1966-04-05      # DATE
  os_lib: #system           # other context is a FRAGMENT
  now: os_lib.now           # DATETIME 'now' is an attribute of system
  today: now.date           # DATE 'today' is an attribute of DATETIME
  alive: today - birthday   # DURATION
  age: alive.years          # INTEGER 'years' is an attr of DURATION

  # this can also be written in one line:

  age: (#system.now.date - 1966-04-05).years

Or some backup configuration lines:

  backup_needed: #system.now.day_of_week <= 5    # Monday = 1
  backup_start: 23:00:00
  backup_max_duration: PT2H30M
  backup_dir: "/var/tmp/backups"
  backup_name: backup_dir ~ '/' ~ "backup-" ~ weekday ~ ".tgz"

The application which uses this configuration, will run the expressions with the names as listed. It may also provide some own formulas, fragments, and helper methods as features.

Operators

As prefix operator, you can use not, -, +, and exists on applicable data types. The # (fragment) and . (attributes) prefixes are weird cases: see Math::Formula::Context.

Operators only work on specific data types, but some types will automatically convert. For instance, all types can be cast into a string to support regular expression and pattern matching.

Of course, you can use parenthesis for grouping.

Prefix operators always have the highest priority, and work right to left (RTL) The infix and ternary operators have the following priorities: (from low to higher, each like with equivalent priority)

  LTR       ?:                             # if ? then : else
  NOCHAIN   ->                             # if-then, substitute
  LTR       or   xor  //                   # (excl)or, defaults to
  LTR       and                            # and
  NOCHAIN   <    >    <=   ==   !=   <=>   # numeric comparison
  NOCHAIN   lt   gt   le   eq   ne   cmp   # string comparison
  LTR       +    -    ~                    # plus, minus, concat
  LTR       *    /    %                    # mul, div, modulo
  NOCHAIN   =~   !~   like  unlike         # regexps and patterns
  LTR       #    .                         # fragments and attributes

The first value is a constant representing associativity. Either the constant LTR (compute left to right), RTL (right to left), or NOCHAIN (non-stackable operator).

Comparison operators

Some data types support numeric comparison (implement <=>, the spaceship operator), other support textual comparison (implement cmp ), where also some types have no intrinsic order.

The <=> and cmp return an integer: -1, 0, or 1, representing smaller, equal, larger.

  :num: :text:
    <     lt      less than/before
    <=    le      less-equal
    ==    eq      equal/the same
    !-    ne      unequal/different
    >=    ge      greater-equal
    >     gt      greater/larger

String comparison uses Unicode::Collate, which might be a bit expensive, but at least a better attempt to order UTF-8 correctly.

SEE ALSO

This module is part of Math-Formula distribution version 0.16, built on March 14, 2023. Website: http://perl.overmeer.net/CPAN/

LICENSE

Copyrights 2023 by [Mark Overmeer <markov@cpan.org>]. For other contributors see ChangeLog.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See http://dev.perl.org/licenses/