.. include:: ../global.rst

Evaluator Functions
-------------------


.. _`evaluate/evaluate`:

.. idio:function:: evaluate/evaluate src [args]


   
   evaluate Idio source code `src` in the context of evaluation
   environment `eenv` and return intermediate code for the code generator
   
   :param src: Idio source code
   :type src: Abstract Syntax Tree
   :param eenv: evaluation environment, defaults to a new instance
   :type eenv: struct-instance, optional
   
   .. seealso: :ref:`%evaluation-environment <evaluate/%evaluation-environment>`


.. _`symbol-value`:

.. idio:function:: symbol-value sym mod [default]


   Return the value of `sym` in `mod` or `default` if supplied	
   						
   :param sym: symbol to query			
   :type sym: symbol				
   :param mod: module to query			
   :type mod: module or name			
   :param default: (optional) value to return if `sym` is not defined in `mod`	
   :type defined: any				
   :return: value or `default`			


.. _`cond-expand`:

.. idio:template:: cond-expand clauses


   ``cond-expand`` reduces `clauses` to the first
   :token:`~SRFI-0:cond_expand_clause` where the clause's
   :token:`~SRFI-0:feature_requirement` is `true`
   
   ``cond-expand`` is a template and so, in effect, it reduces the set of
   `clauses` supplied to just the first that is `true`.
   
   The :token:`~SRFI-0:feature_requirement` for each clause in `clauses`
   is constructed from the presence of
   :token:`~SRFI-0:feature_identifier`\ s or logical combinations of
   those features.  The features themselves are set by :program:`idio` or
   can be augmented by users.
   
   The `clauses` for ``cond-expand`` are interpreted as the (SRFI-0_)
   grammar :token:`~SRFI-0:conditional_expansion_form`:
   
   .. productionlist:: SRFI-0
      conditional_expansion_form :   (cond-expand `cond_expand_clause`+)
   			      : | (cond-expand `cond_expand_clause`* (else expression*))
      cond_expand_clause : (`feature_requirement` expression*)
      feature_requirement :   `feature_identifier`
   		       : | (and `feature_requirement`*)
   		       : | (or  `feature_requirement`*)
   		       : | (not `feature_requirement`)
      feature_identifier : a symbol or string, see below
   
   :Example:
   
   Several tests of standard library calls in :ref:`libc <libc module>`
   differ between operating systems.  We can specialize as appropriate
   and ``cond-expand`` results in just a single ``libc-wrap-error-load``
   expression in the byte code.
   
   .. code-block:: idio
   
      (cond-expand
       ((or "uname/sysname/FreeBSD"
            "uname/sysname/OpenBSD"
            "uname/sysname/Darwin") {
         libc-wrap-error-load "libc-wrap-errors/EGID-set-invalid-gid.idio" "Operation not permitted" EPERM "setegid"
       })
       (else {
         libc-wrap-error-load "libc-wrap-errors/EGID-set-invalid-gid.idio" "Invalid argument" EINVAL "setegid"
       })
      )
   
   .. seealso:: :ref:`Idio features` and :ref:`%add-feature <%add-feature>`
   
   

.. _`%add-feature`:

.. idio:function:: %add-feature f


   add feature `f` to Idio features			
   							
   :param f: feature to add				
   :type f: symbol or string				
   :return: new list of features				




.. include:: ../commit.rst