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package parser
import (
"github.com/gnolang/parscan/scanner"
)
const (
Stmt = 1 << iota
ExprSep
Call
Index
Decl
)
type NodeSpec struct {
Kind // AST node kind
Flags uint // composable properties used for AST generation
Order int // operator precedence order
}
type Parser struct {
*scanner.Scanner
Spec map[string]NodeSpec
}
func (p *Parser) Parse(src string) (n []*Node, err error) {
tokens, err := p.Scan(src)
if err != nil {
return
}
return p.ParseTokens(tokens)
}
func (p *Parser) ParseTokens(token []scanner.Token) (roots []*Node, err error) {
// TODO: error handling.
var root *Node // current root node
var expr *Node // current expression root node
var prev, c *Node
var lce *Node
for i, t := range token {
prev = c
c = &Node{
Token: t,
Kind: p.Spec[t.Name()].Kind,
unary: t.Kind() == scanner.Operator && (i == 0 || token[i-1].Kind() == scanner.Operator),
}
if c.Kind == 0 {
switch t.Kind() {
case scanner.Number:
c.Kind = p.Spec["#num"].Kind
case scanner.Identifier:
c.Kind = p.Spec["#id"].Kind
}
}
if root == nil {
if p.isSep(c) {
continue
}
lce = nil
root = c
if p.isExpr(c) {
expr = c
}
continue
}
if t.Kind() == scanner.Block {
if expr != nil {
if p.hasBlockProp(c, ExprSep) && p.isExprSep(root) {
// A bracket block may end a previous expression.
root.Child = append(root.Child, expr)
expr = nil
} else if p.hasBlockProp(c, Call) && !p.hasProp(root, Decl) && p.canCallToken(token[i-1]) {
// Handle (possibly nested) call expressions.
if lce == nil || lce != expr { // TODO(marc): not general, fix it.
lce = prev
}
lce.Child = []*Node{{Token: lce.Token, Child: lce.Child, Kind: lce.Kind}}
lce.Token = scanner.NewToken("Call", c.Pos())
lce.Kind = p.Spec["#call"].Kind
}
}
tcont := t.Content()
s := tcont[t.Start() : len(tcont)-t.End()]
n2, err := p.Parse(s)
if err != nil {
return nil, err
}
c.Child = append(c.Child, n2...)
}
// Process the end of an expression or a statement.
if t.Kind() == scanner.Separator {
if expr != nil && p.hasProp(root, Stmt) {
root.Child = append(root.Child, expr)
if p.hasBlockProp(expr, ExprSep) {
roots = append(roots, root)
root = nil
}
expr = nil
} else {
if expr != nil {
root = expr
}
roots = append(roots, root)
expr = nil
root = nil
}
continue
}
// We assume from now that current node is part of an expression subtree.
if expr == nil {
if p.isStatement(root) {
expr = c
continue
}
expr = root
}
// Update the expression subtree according to binary operator precedence rules.
// - operators are binary infix by default.
// - if an operator follows another, then it's unary prefix.
// - if an expression starts by an operator, then it's unary prefix.
// - non operator nodes have a default precedence of 0.
// TODO: handle postfix unary (i.e. ++) and ternary (i.e. ?:)
//
ep := p.Spec[expr.Content()].Order
cp := p.Spec[c.Content()].Order
a := expr
if c.unary {
cp = 0
}
if cp != 0 {
if cp > ep {
// Perform an operator permutation at expr root as required by precedence.
// TODO(marc): maybe it can be generalized in below else branch.
expr, c = c, expr
a = expr // Temporary ancestor: its children may have to be permuted.
} else {
// Findout if an operator permutation is necessary in subtree.
c1 := expr
for {
a = c1
if c1.unary {
c1, c = c, c1
a = c1
if c == expr {
expr = a
}
break
}
if len(c1.Child) < 2 {
break
}
c1 = c1.Child[1]
if c1.Token.Kind() != scanner.Operator || c1.unary || cp > p.Spec[c1.Content()].Order {
break
}
}
// No permutation occured. Append current to last visited ancestor.
if len(a.Child) > 1 {
a.Child = a.Child[:1]
c.Child = append(c.Child, c1)
}
}
} else if ep != 0 {
for len(a.Child) > 1 {
a = a.Child[1]
}
}
a.Child = append(a.Child, c)
if p.hasProp(a, Call) {
lce = a
}
}
if root != nil && p.isStatement(root) {
if expr != nil {
root.Child = append(root.Child, expr)
}
} else if expr != nil {
root = expr
}
if root != nil {
roots = append(roots, root)
}
return roots, err
}
func (p *Parser) hasProp(n *Node, prop uint) bool { return p.Spec[n.Name()].Flags&prop != 0 }
func (p *Parser) isStatement(n *Node) bool { return p.Spec[n.Content()].Flags&Stmt != 0 }
func (p *Parser) isExprSep(n *Node) bool { return p.Spec[n.Content()].Flags&ExprSep != 0 }
func (p *Parser) isExpr(n *Node) bool { return !p.isStatement(n) && !p.isExprSep(n) }
func (p *Parser) isSep(n *Node) bool { return n.Token.Kind() == scanner.Separator }
func (p *Parser) IsBlock(n *Node) bool { return n.Token.Kind() == scanner.Block }
func (p *Parser) hasBlockProp(n *Node, prop uint) bool {
return p.Spec[n.Content()[:n.Start()]].Flags&prop != 0
}
func (p *Parser) precedenceToken(t scanner.Token) int {
s := t.Content()
if l := t.Start(); l > 0 {
s = s[:l]
}
return p.Spec[s].Order
}
func (p *Parser) canCallToken(t scanner.Token) bool {
return p.precedenceToken(t) == 0 || p.Spec[t.Name()].Flags&Call != 0
}
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