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Andrew Main (Zefram) > Parse-Perl > Parse::Perl



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Module Version: 0.007   Source  


Parse::Perl - interpret string as Perl source


        use Parse::Perl qw(current_environment);

        $env = current_environment;

        use Parse::Perl qw(parse_perl);

        $func = parse_perl($env, '$foo + 3');


This module provides the capability to parse a string at runtime as Perl source code, so that the resulting compiled code can be later executed. This is part of the job of the string form of the eval operator, but in this module it is separated out from the other jobs of eval. Parsing of Perl code is generally influenced by its lexical context, and this module provides some explicit control over this process, by reifying lexical environments as Perl objects.

Perl's built-in eval operator (in string form) actually performs four distinct jobs: capture lexical environment, parse Perl source, execute code, and catch exceptions. This module allows each of these four jobs to be performed separately, so they can then be combined in ways that eval doesn't permit. Capturing lexical environment is performed using a special operator supplied by this module. Parsing Perl source is performed by a function supplied by this module. Executing code is adequately handled by Perl's native mechanisms for calling functions through references. Finally, exception catching is handled by the block form of eval.



This operator generates a Parse::Perl::Environment object which encapsulates the lexical environment at the site where the operator is used. It evaluates to a reference to the environment object. The environment object encapsulates the lexical variables that are available at this site, the lexical warning status, and the effects of all other lexical pragmata.

This operator captures all the lexical variables that are visible at the point where it is used. This can result in surprisingly long lifetimes for variables in enclosing scopes. This aspect of this operator is unlike eval, which only captures those variables that are referenced in the directly enclosing function, leading to "Variable not available" warnings.

This operator should be used through bareword function call syntax, as if it were a function. However, it cannot otherwise be called as a function in the normal manner. Attempting to take a reference to it will result in a code reference that does not have any of the behaviour described.



ENVIRONMENT must be a reference to a Parse::Perl::Environment object, which encapsulates a lexical environment. SOURCE must be a string. SOURCE is parsed as a block of Perl code (specifically, as if it were the body of a function), in the lexical environment represented by ENVIRONMENT. If there is any error in compilation, a suitable exception is thrown. If there is no error, the compiled code is returned, in the form of a reference to a Perl function. The code represented by SOURCE can then be executed by calling the function.


Parse::Perl::Environment, "eval" in perlfunc


Andrew Main (Zefram) <>


Copyright (C) 2009, 2010, 2011, 2012 Andrew Main (Zefram) <>


This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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