Math::Expression::Evaluator::Parser - Parse mathematical expressions
use Math::Expression::Evaluator::Parser; my $exp = '2 + a * 4'; my $ast = Math::Expression::Evaluator::Parser::parse($exp, {}); # $ast is now something like this: # $ast = ['+', # 2, # ['*', # ['$', 'a'], # 4 # ] # ];
This module parses a mathematical expression in usual notation, and turns it into an Abstract Syntax Tree (AST).
If you want to have a simple interface and want to evaluate these ASTs, use Math::Expression::Evaluator.
The following description of the AST structure matches the current implementation, but really is an implementation detail that's subject to change without further notice. In particular a possible addition of meta information (like file and line numbers) might require a change of structure.
The AST is a tree that consists of nested array refs. The first item is a string (until now always a single character), and denotes the type of the node. The rest of the items in the array is a list of its arguments.
For the mathematical symbols +
, -
, *
, /
, ^
(exponentation) this is straight forward, but /
and -
are always treated as prefix ops, so the string '2 - 3' is actually turned into ['+', 2, ['-', 3]]
.
Other AST nodes are
['$', $var_name]
represents a variable.
['{', $expr1, $expr2, ... ]
represents a block, i.e. a list of expressions.
['=', $var, $expr]
represents an assignment, where $expr
is assigned to $var
.
['&', $name, @args]
is a function toll to the function called $name
.
parse
takes a string and a hash ref, where the hash ref takes configuration parameters. Currently the only allowed option is force_semicolon
. If set to a true value, it forces statements to be forced by semicolons (so 2 3
will be forbidden, 2; 3
is still allowed).
parse
throws an exception on parse errors.