FSharpCompiler.Yacc 1.1.7

Yacc is a tool which given a context-free grammar, constructs a parsing table used for parser which will parse input tokens according to the grammar rules.

Unlike traditional Yacc tools, FSharpCompiler.Yacc does not require action in rules. Instead of explicitly actions, the parse tree is implicitly constructed during the parse. As the parser executes, it builds an internal representation of the the structure of the program. The internal representation is based on the right hand side of the production rules. When a right hand side is recognized, it is reduced to the corresponding left hand side. Parsing is complete when the entire program has been reduced to the start symbol of the grammar. The specification of context-free grammar input see [The Yacc Input File](Yacc Input File.md)

Build a parsing table

From the input file yaccFile, the method for generating the ExprParsingTable module is follow:

open FSharpCompiler.Yacc

let yacc = YaccFile.parse yaccFile
let parseTbl = 
	ParseTable.create(yacc.mainRules, yacc.precedences)

// ... the print ExprParsingTable code with parseTbl

The result module like this:

module ArithmeticExpressions.ExprParsingTable

let rules = set [ ... ]
let kernelSymbols = Map [ ... ]
let parsingTable = set [ ... ]

With the parsing table, plus the parser runtime libraries, FSharpCompiler.Parsing, you can build parsers. How to build a parser using Yacc is detailed in the resolution:xp44mm/ArithmeticExpressions

The Grammar Type

The Grammar type gives you some properties that represent important Sets of symbols. Grammar is obtained by this method:

let grammar = 
    let yacc = YaccFile.parse yaccFile
    Grammar.from yacc.mainRules

yaccFile is the yacc input file content. The main collection properties are included:

grammar.symbols:      Set<string> // set of terminals and nonterminals
grammar.nonterminals: Set<string> // set of nonterminals
grammar.nullables:    Set<string> // set of nonterminals, which is able to empty
grammar.firsts:       Map<string,Set<string>> // A dictionary that queries the nonterminal's FIRST collection
grammar.lasts:        Map<string,Set<string>> // A dictionary that queries the nonterminal's LAST collection
grammar.follows:      Map<string,Set<string>> // A dictionary that queries the nonterminal's FOLLOW collection

These properties are commonly used to help you write regular expressions in Lex input file.