(R-lang.info)Evaluation of expressions

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3 Evaluation of expressions
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When a user types a command at the prompt (or when an expression is read
from a file) the first thing that happens to it is that the command is
transformed by the parser into an internal representation.  The
evaluator executes parsed R expressions and returns the value of the
expression.  All expressions have a value.  This is the core of the
language.

   This chapter describes the basic mechanisms of the evaluator, but
avoids discussion of specific functions or groups of functions which are
described in separate chapters later on or where the help pages should
be sufficient documentation.

   Users can construct expressions and invoke the evaluator on them.

Simple evaluation

Control structures

Elementary arithmetic operations

Indexing

Scope of variables