languageEl              package:methods              R Documentation

Elements of Language Objects

Description:

     Internal routines to support some operations on language objects.

Usage:

     languageEl(object, which)

     isGrammarSymbol(symbol)

Summary of Functions:

     'languageEl': extract an element of a language object,
          consistently for different kinds of objects.

          The 1st., etc. elements of a function are the corresponding
          formal arguments, with the default expression if any as
          value.

          The first element of a call is the name or the function
          object being called.  

          The 2nd, 3rd, etc. elements are the 1st, 2nd, etc. arguments
          expressions.  Note that the form of the extracted name is
          different for R and S-Plus.  When the name (the first
          element) of a call is replaced, the languageEl replacement
          function coerces a character string to the internal form for
          each system.

          The 1st, 2nd, 3rd elements of an 'if' expression are the
          test, first, and second branch.

          The 1st element of a 'for' object is the name (symbol) being
          used in the loop, the second is the expression for the range
          of the loop, the third is the body of the loop.

          The first element of a 'while' object is the loop test, and
          the second the body of the loop.


     'isGrammarSymbol': Checks whether the symbol is part of the
          grammar. Don't use this function directly.

