logik2021/codego/aussagenlogik/schema/schema.go

package schema

import (
	"logik/aussagenlogik/formulae"
	parser "logik/grammars/aussagenlogik"
	"regexp"

	"github.com/antlr/antlr4/runtime/Go/antlr"
)

/* ---------------------------------------------------------------- *
 * EXPORTS
 * ---------------------------------------------------------------- */

func ParseExpr(u string) formulae.Formula {
	var lexer = createLexer(u)
	var tokenStream = lexerToTokenStream(lexer)
	var prs = parser.NewaussagenlogikParser(tokenStream)
	var t = prs.Start()
	tree := createFormula(t, prs)
	return tree
}

/* ---------------------------------------------------------------- *
 * PRIVATE
 * ---------------------------------------------------------------- */

func exprToStream(u string) *antlr.InputStream {
	return antlr.NewInputStream(u)
}

func lexerToTokenStream(lexer antlr.Lexer) antlr.TokenStream {
	return antlr.NewCommonTokenStream(lexer, antlr.TokenDefaultChannel)
}

func createLexer(u string) antlr.Lexer {
	stream := exprToStream(u)
	return parser.NewaussagenlogikLexer(stream)
}

func createFormula(tree antlr.Tree, parser antlr.Parser) formulae.Formula {
	var ant = antlrTree{tree: tree, parser: &parser}
	return ant.toFormula()
}

/* ---------------------------------------------------------------- *
 * Struct: antlrTree + Methods
 * ---------------------------------------------------------------- */

type antlrTree struct {
	tree   antlr.Tree
	parser *antlr.Parser
}

func (ant antlrTree) getChildren() []antlrTree {
	var nodes = ant.tree.GetChildren()
	var subants = make([]antlrTree, len(nodes))
	for i, node := range nodes {
		subants[i] = antlrTree{tree: node, parser: ant.parser}
	}
	return subants
}

func (ant antlrTree) getLabel() string {
	return antlr.TreesGetNodeText(ant.tree, []string{}, *ant.parser)
}

func (ant antlrTree) getTextContent() string {
	var expr string = ""
	var subants = ant.getChildren()
	if len(subants) == 0 {
		return ant.getLabel()
	}
	for _, subant := range subants {
		expr += subant.getTextContent()
	}
	return expr
}

func (ant antlrTree) toFormula() formulae.Formula {
	var label string = ant.getLabel()
	var subants = ant.getChildren()
	var nChildren = len(subants)

	switch label {
	case "start":
		if nChildren == 1 {
			return subants[0].toFormula()
		}
	case "open":
		if nChildren == 1 {
			return subants[0].toFormula()
		}
	case "closed":
		switch nChildren {
		case 1:
			return subants[0].toFormula()
		// expr = ( expr )
		case 3:
			return subants[1].toFormula()
		}
	case "atomic":
		if nChildren == 1 {
			return subants[0].toFormula()
		}
	case "taut":
		return formulae.Tautology
	case "contradiction":
		return formulae.Contradiction
	case "atom":
		name := ant.getTextContent()
		return formulae.Atom(name)
	case "generic":
		re := regexp.MustCompile(`^{|}$`)
		name := string(re.ReplaceAll([]byte(ant.getTextContent()), []byte("")))
		return formulae.Generic(name)
	case "not":
		// NOTE: expr = ! expr
		if nChildren == 2 {
			return formulae.Negation(subants[1].toFormula())
		}
	case "and2":
		// NOTE: expr = expr && expr
		if nChildren == 3 {
			return formulae.Conjunction2(subants[0].toFormula(), subants[2].toFormula())
		}
	case "or2":
		// NOTE: expr = expr || expr
		if nChildren == 3 {
			return formulae.Disjunction2(subants[0].toFormula(), subants[2].toFormula())
		}
	case "implies":
		// NOTE: expr = expr -> expr
		if nChildren == 3 {
			return formulae.Implies(subants[0].toFormula(), subants[2].toFormula())
		}
	case "iff":
		// NOTE: expr = expr <=> expr
		if nChildren == 3 {
			return formulae.DoubleImplication(subants[0].toFormula(), subants[2].toFormula())
		}
	case "and", "or":
		// NOTE: expr = expr op expr op ... op expr
		var n int = int((len(subants) + 1) / 2)
		if nChildren == 2*n-1 && n >= 2 {
			var subtrees = make([]formulae.Formula, n)
			var isSymb bool = true
			var i int = 0
			for _, subant := range subants {
				if isSymb {
					subtrees[i] = subant.toFormula()
					i++
				}
				// NOTE: infix notation: alternatives between expression and symbol
				isSymb = !isSymb
			}
			switch label {
			case "and":
				return formulae.Conjunction(subtrees)
			case "or":
				return formulae.Disjunction(subtrees)
			}
		}
	}

	panic("Could not parse expression")
}