path: root/driver/parser.go

package driver

import (
	"fmt"
	"io"
	"strings"

	mldriver "github.com/nihei9/maleeni/driver"
	mlspec "github.com/nihei9/maleeni/spec"
	"github.com/nihei9/vartan/spec"
)

type Node struct {
	KindName string
	Text     string
	Children []*Node
}

func PrintTree(w io.Writer, node *Node) {
	printTree(w, node, "", "")
}

func printTree(w io.Writer, node *Node, ruledLine string, childRuledLinePrefix string) {
	if node == nil {
		return
	}

	if node.Text != "" {
		fmt.Fprintf(w, "%v%v %#v\n", ruledLine, node.KindName, node.Text)
	} else {
		fmt.Fprintf(w, "%v%v\n", ruledLine, node.KindName)
	}

	num := len(node.Children)
	for i, child := range node.Children {
		var line string
		if num > 1 && i < num-1 {
			line = "├─ "
		} else {
			line = "└─ "
		}

		var prefix string
		if i >= num-1 {
			prefix = "    "
		} else {
			prefix = "│  "
		}

		printTree(w, child, childRuledLinePrefix+line, childRuledLinePrefix+prefix)
	}
}

type semanticFrame struct {
	cst *Node
	ast *Node
}

type Parser struct {
	gram       *spec.CompiledGrammar
	lex        *mldriver.Lexer
	stateStack []int
	semStack   []*semanticFrame
	cst        *Node
	ast        *Node
}

func NewParser(gram *spec.CompiledGrammar, src io.Reader) (*Parser, error) {
	lex, err := mldriver.NewLexer(gram.LexicalSpecification.Maleeni.Spec, src)
	if err != nil {
		return nil, err
	}

	return &Parser{
		gram:       gram,
		lex:        lex,
		stateStack: []int{},
		semStack:   []*semanticFrame{},
	}, nil
}

func (p *Parser) Parse() error {
	termCount := p.gram.ParsingTable.TerminalCount
	p.push(p.gram.ParsingTable.InitialState)
	tok, err := p.nextToken()
	if err != nil {
		return err
	}
	for {
		var tsym int
		if tok.EOF {
			tsym = p.gram.ParsingTable.EOFSymbol
		} else {
			tsym = p.gram.LexicalSpecification.Maleeni.KindToTerminal[tok.KindID]
		}
		act := p.gram.ParsingTable.Action[p.top()*termCount+tsym]
		switch {
		case act < 0: // Shift
			tokText := tok.Text()
			tok, err = p.shift(act * -1)
			if err != nil {
				return err
			}

			// semantic action
			p.semStack = append(p.semStack, &semanticFrame{
				cst: &Node{
					KindName: p.gram.ParsingTable.Terminals[tsym],
					Text:     tokText,
				},
				ast: &Node{
					KindName: p.gram.ParsingTable.Terminals[tsym],
					Text:     tokText,
				},
			})
		case act > 0: // Reduce
			accepted := p.reduce(act)
			if accepted {
				top := p.semStack[len(p.semStack)-1]
				p.cst = top.cst
				p.ast = top.ast
				return nil
			}

			// semantic action

			prodNum := act
			lhs := p.gram.ParsingTable.LHSSymbols[prodNum]

			// When an alternative is empty, `n` will be 0, and `handle` will be empty slice.
			n := p.gram.ParsingTable.AlternativeSymbolCounts[prodNum]
			handle := p.semStack[len(p.semStack)-n:]

			var cst *Node
			{
				children := make([]*Node, len(handle))
				for i, f := range handle {
					children[i] = f.cst
				}
				cst = &Node{
					KindName: p.gram.ParsingTable.NonTerminals[lhs],
					Children: children,
				}
			}

			var ast *Node
			{
				act := p.gram.ASTAction.Entries[prodNum]
				children := []*Node{}
				if act != nil {
					for _, e := range act {
						if e > 0 {
							offset := e - 1
							children = append(children, handle[offset].ast)
						} else {
							offset := e*-1 - 1
							for _, c := range handle[offset].ast.Children {
								children = append(children, c)
							}
						}
					}
				} else {
					// If an alternative has no AST action, a driver generates
					// a node with the same structure as a CST.
					for _, f := range handle {
						children = append(children, f.ast)
					}
				}
				ast = &Node{
					KindName: p.gram.ParsingTable.NonTerminals[lhs],
					Children: children,
				}
			}

			p.semStack = p.semStack[:len(p.semStack)-n]
			p.semStack = append(p.semStack, &semanticFrame{
				cst: cst,
				ast: ast,
			})
		default:
			var tokText string
			if tok.EOF {
				tokText = "<EOF>"
			} else {
				tokText = fmt.Sprintf("%v (%v)", tok.KindName.String(), tok.Text())
			}

			eKinds, eof := p.expectedKinds(p.top())

			var b strings.Builder
			fmt.Fprintf(&b, "%v", eKinds[0])
			for _, k := range eKinds[1:] {
				fmt.Fprintf(&b, ", %v", k)
			}
			if eof {
				if len(eKinds) > 0 {
					fmt.Fprintf(&b, ", <EOF>")
				} else {
					fmt.Fprintf(&b, "<EOF>")
				}
			}

			return fmt.Errorf("unexpected token: %v, expected: %v", tokText, b.String())
		}
	}
}

func (p *Parser) nextToken() (*mldriver.Token, error) {
	skip := p.gram.LexicalSpecification.Maleeni.Skip
	for {
		tok, err := p.lex.Next()
		if err != nil {
			return nil, err
		}
		if tok.Invalid {
			return nil, fmt.Errorf("invalid token: '%v'", tok.Text())
		}

		if skip[tok.KindID] > 0 {
			continue
		}

		return tok, nil
	}
}

func (p *Parser) shift(nextState int) (*mldriver.Token, error) {
	p.push(nextState)
	return p.nextToken()
}

func (p *Parser) reduce(prodNum int) bool {
	tab := p.gram.ParsingTable
	lhs := tab.LHSSymbols[prodNum]
	if lhs == tab.LHSSymbols[tab.StartProduction] {
		return true
	}
	n := tab.AlternativeSymbolCounts[prodNum]
	p.pop(n)
	nextState := tab.GoTo[p.top()*tab.NonTerminalCount+lhs]
	p.push(nextState)
	return false
}

func (p *Parser) top() int {
	return p.stateStack[len(p.stateStack)-1]
}

func (p *Parser) push(state int) {
	p.stateStack = append(p.stateStack, state)
}

func (p *Parser) pop(n int) {
	p.stateStack = p.stateStack[:len(p.stateStack)-n]
}

func (p *Parser) CST() *Node {
	return p.cst
}

func (p *Parser) AST() *Node {
	return p.ast
}

func (p *Parser) expectedKinds(state int) ([]mlspec.LexKindName, bool) {
	kinds := []mlspec.LexKindName{}
	eof := false
	terms := p.gram.ParsingTable.ExpectedTerminals[state]
	for _, tsym := range terms {
		if tsym == 1 {
			eof = true
			continue
		}

		kindID := p.gram.LexicalSpecification.Maleeni.TerminalToKind[tsym]
		kindName := p.gram.LexicalSpecification.Maleeni.Spec.KindNames[kindID]
		kinds = append(kinds, kindName)
	}

	return kinds, eof
}