TParser - Dynamic Parser Machine

Source: source/classes/tparser.prg

TParser is a generic grammar-rule engine skeleton. It maintains a list of production rules and a state stack. Rules consist of a non-terminal symbol, a token array, and an action code block. This class provides the framework for building expression parsers, command interpreters, or domain-specific language processors.

Key DATA Members

DATA	Type	Description
`aRules`	Array	Array of grammar rules, each { cNonTerminal, aTokens, bAction }
`aStates`	Array	State stack for parsing; state 0 is empty by default

Methods

Method	Description
`New()`	Create a new parser with empty rules and initial state
`Add( cNonTerminal, aTokens, bAction )`	Add a production rule: non-terminal -> sequence of tokens with action

Example: Add Grammar Rules

#include "FiveWin.ch"

function Main()

   local oParser := TParser():New()

   // expr -> number
   oParser:Add( "expr", { "number" }, {|n| n } )

   // expr -> expr + expr
   oParser:Add( "expr", { "expr", "+", "expr" }, {|a,b| a + b } )

   // expr -> expr * expr
   oParser:Add( "expr", { "expr", "*", "expr" }, {|a,b| a * b } )

   // Access the rules
   ? Len( oParser:aRules )   // 3 rules added

return nil

Notes

TParser is a skeleton class. The core Add() method builds the rule table; you must implement the tokenizer and the parsing algorithm (shift-reduce, recursive descent, etc.) yourself using the aRules and aStates data.
Each rule's aTokens array defines the expected token sequence; the bAction block is the semantic action fired when the rule matches.
aStates starts with a single empty state (index 0). States can be pushed/popped during parsing to handle nested constructs.

TParser - Dynamic Parser Machine

Key DATA Members

Methods

Example: Add Grammar Rules

Notes

See Also