(bison.info) Parser States

Info Catalog

(bison.info) Contextual Precedence

(bison.info) Algorithm

(bison.info) Reduce/Reduce

 
 Parser States
 =============
 
    The function `yyparse' is implemented using a finite-state machine.
 The values pushed on the parser stack are not simply token type codes;
 they represent the entire sequence of terminal and nonterminal symbols
 at or near the top of the stack.  The current state collects all the
 information about previous input which is relevant to deciding what to
 do next.
 
    Each time a look-ahead token is read, the current parser state
 together with the type of look-ahead token are looked up in a table.
 This table entry can say, "Shift the look-ahead token."  In this case,
 it also specifies the new parser state, which is pushed onto the top of
 the parser stack.  Or it can say, "Reduce using rule number N."  This
 means that a certain number of tokens or groupings are taken off the
 top of the stack, and replaced by one grouping.  In other words, that
 number of states are popped from the stack, and one new state is pushed.
 
    There is one other alternative: the table can say that the
 look-ahead token is erroneous in the current state.  This causes error
 processing to begin ( Error Recovery.).
 

Info Catalog

(bison.info) Contextual Precedence

(bison.info) Algorithm

(bison.info) Reduce/Reduce