feat: add support for control flow operators in expressions

Logical operators `&&` (and), `||` (or) are now parsed in expressions.
The control flow tokens (labels, conditional jumps) are added
accordingly.

1 files changed, 187 insertions, 0 deletions

diff --git a/parser/expr.go b/parser/expr.go
new file mode 100644
index 0000000..18c97a5
--- /dev/null
+++ b/parser/expr.go
@@ -0,0 +1,187 @@
+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.
+}