Top-down parser with from bottom to top

Source: Internet
Author: User

First define a syntax

From top to bottom:

Eliminate direct left recursion: convert a-a+b/b to A-ba ' A '-+ba '/null

Elimination of indirect left recursion: an arbitrary order for non-terminator rules. The recursive implementation can only be derived from small to large, and it is converted to direct left recursion.

No backtracking implementation: constructs first Fllow and first+.

First, the starting symbol is pushed into the stack, the symbol is deduced (according to the table table is the relevant first+ to select the rule), the deduced symbol except the first symbol pushed into the stack, and then loop the process, when the non-terminator occurs, the input is matched, and then the next input is processed.

Top-down parser with from bottom to top

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