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package parser
import (
"log"
"strconv"
"github.com/gnolang/parscan/lang"
"github.com/gnolang/parscan/scanner"
)
func (p *Parser) ParseExpr(in Tokens) (out Tokens, err error) {
log.Println("ParseExpr in:", in)
var ops Tokens
var vl int
//
// Process tokens from last to first, the goal is to reorder the tokens in
// a stack machine processing order, so it can be directly interpreted.
//
for i := len(in) - 1; i >= 0; i-- {
t := in[i]
// temporary assumptions: binary operators, returning 1 value
switch t.Id {
case lang.Ident:
// resolve symbol if not a selector rhs.
// TODO: test for selector expr.
_, sc, ok := p.getSym(t.Str, p.scope)
if ok {
if sc != "" {
t.Str = sc + "/" + t.Str
}
}
out = append(out, t)
vl++
case lang.Int, lang.String:
out = append(out, t)
vl++
case lang.Define, lang.Add, lang.Sub, lang.Assign, lang.Equal, lang.Greater, lang.Less, lang.Mul, lang.Land, lang.Lor:
if vl < 2 {
ops = append(ops, t)
break
}
case lang.ParenBlock:
// If the previous token is an arithmetic, logic or assign operator then
// this parenthesis block is an enclosed expr, otherwise a call expr.
if i == 0 || in[i-1].Id.IsOperator() {
out = append(out, t)
vl++
break
}
// The call expression can be a function call, a conversion,
// a type assersion (including for type switch)
// func call: push args and func address then call
out = append(out, t)
vl++
if t2 := in[i-1]; t2.Id == lang.Ident {
if s, sc, ok := p.getSym(t2.Str, p.scope); ok {
log.Println("callExpr:", t2.Str, p.scope, s, ok, sc)
if s.kind == symValue {
// Store the number of input parameters in the token Beg field.
ops = append(ops, scanner.Token{Str: "callX", Id: lang.CallX, Pos: t.Pos, Beg: p.numItems(t.Block(), lang.Comma)})
break
}
}
}
ops = append(ops, scanner.Token{Str: "call", Id: lang.Call, Pos: t.Pos})
}
if lops, lout := len(ops), len(out); lops > 0 && vl > lops {
op := ops[lops-1]
ops = ops[:lops-1]
// Reorder tokens according to operator precedence rules.
if p.precedence(out[lout-2]) > p.precedence(op) {
op, out[lout-1], out[lout-2] = out[lout-2], op, out[lout-1]
if p.precedence(out[lout-3]) > p.precedence(out[lout-1]) {
out[lout-1], out[lout-2], out[lout-3] = out[lout-3], out[lout-1], out[lout-2]
}
}
out = append(out, op)
vl--
}
}
out = append(out, ops...)
log.Println("ParseExpr out:", out, "vl:", vl, "ops:", ops)
// A logical operator (&&, ||) involves additional control flow operations.
if out, err = p.ParseLogical(out); err != nil {
return out, err
}
if l := len(out) - 1; out[l].Id == lang.Define || out[l].Id == lang.Assign {
// Handle the assignment of a logical expression.
s1 := p.subExprLen(out[:l])
head, err := p.ParseLogical(out[:l-s1])
if err != nil {
return out, err
}
out = append(head, out[l-s1:]...)
}
// The tokens are now properly ordered, process nested blocks.
for i := len(out) - 1; i >= 0; i-- {
t := out[i]
var toks Tokens
switch t.Id {
case lang.ParenBlock, lang.BracketBlock:
if toks, err = p.ParseExprStr(t.Block()); err != nil {
return out, err
}
default:
continue
}
// replace block token by its parsed result.
log.Println("toks:", toks)
out2 := append(Tokens{}, out[:i]...)
out2 = append(out2, toks...)
out = append(out2, out[i+1:]...)
}
log.Println("Final out:", out)
return out, err
}
func (p *Parser) ParseExprStr(s string) (tokens Tokens, err error) {
if tokens, err = p.Scan(s, false); err != nil {
return
}
var result Tokens
for _, sub := range tokens.Split(lang.Comma) {
toks, err := p.ParseExpr(sub)
if err != nil {
return result, err
}
result = append(toks, result...)
}
return result, err
}
// ParseLogical handles logical expressions with control flow (&& and ||) by
// ensuring the left hand side is evaluated unconditionally first, then the
// right hand side can be skipped or not by inserting a conditional jump and label.
// If the last token is not a logical operator then the function is idempotent.
func (p *Parser) ParseLogical(in Tokens) (out Tokens, err error) {
l := len(in) - 1
if !in[l].Id.IsLogicalOp() {
return in, nil
}
xp := strconv.Itoa(p.labelCount[p.scope])
p.labelCount[p.scope]++
rhsIndex := p.subExprLen(in[:l])
lhs, err := p.ParseLogical(in[l-rhsIndex : l])
if err != nil {
return out, err
}
rhs, err := p.ParseLogical(in[:l-rhsIndex])
if err != nil {
return out, err
}
out = append(out, lhs...)
if in[l].Id == lang.Lor {
out = append(out, scanner.Token{Id: lang.JumpSetTrue, Str: "JumpSetTrue " + p.scope + "x" + xp})
} else {
out = append(out, scanner.Token{Id: lang.JumpSetFalse, Str: "JumpSetFalse " + p.scope + "x" + xp})
}
out = append(out, rhs...)
out = append(out, scanner.Token{Id: lang.Label, Str: p.scope + "x" + xp})
return out, err
}
// subExprLen returns the length of the first complete sub-expression starting from the input end.
func (p *Parser) subExprLen(in Tokens) int {
l := len(in) - 1
last := in[l]
switch last.Id {
case lang.Int, lang.Float, lang.String, lang.Char, lang.Ident, lang.ParenBlock, lang.BracketBlock:
return 1
case lang.Call:
s1 := p.subExprLen(in[:l])
return 1 + s1 + p.subExprLen(in[:l-s1])
// TODO: add selector and index operators when ready
}
if last.Id.IsBinaryOp() {
s1 := p.subExprLen(in[:l])
return 1 + s1 + p.subExprLen(in[:l-s1])
}
if last.Id.IsUnaryOp() {
return 1 + p.subExprLen(in[:l])
}
return 0 // should not occur. TODO: diplay some error here.
}
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