Math::Expression::Evaluator::Parser - Parse mathematical expressions
use Math::Expression::Evaluator::Parser;
use Math::Expression::Evaluator::Util qw(simplify_ast);
my $exp = '2 + a * 4';
my $ast = Math::Expression::Evaluator::Parser::parse($exp, {});
$ast = simplify_ast($ast);
# $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 the Math::Expression::Evaluator manpage.
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.
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.