fix: correct and simplify parsing of expressions.

The expressions were parsed from right to left, and it was incorrect and
cumbersome. Now they are processed from left to right, with a simpler
and correct handling of precedence rules.

The vm function call syntax has been changed to set the function
before the input arguments on the stack, as to follow the declaring
order in languages.

1 files changed, 8 insertions, 7 deletions

diff --git a/parser/decl.go b/parser/decl.go
index f6e8102..015f4bd 100644
--- a/parser/decl.go
+++ b/parser/decl.go
@@ -69,7 +69,7 @@ func (p *Parser) parseConstLine(in Tokens) (out Tokens, err error) {
 		values = nil
 	}
 	for i, v := range values {
-		if v, err = p.parseExpr(v); err != nil {
+		if v, err = p.parseExpr(v, ""); err != nil {
 			return out, err
 		}
 		cval, _, err := p.evalConstExpr(v)
@@ -99,11 +99,11 @@ func (p *Parser) evalConstExpr(in Tokens) (cval constant.Value, length int, err
 	id := t.Tok
 	switch {
 	case id.IsBinaryOp():
-		op1, l1, err := p.evalConstExpr(in[:l])
+		op2, l2, err := p.evalConstExpr(in[:l])
 		if err != nil {
 			return nil, 0, err
 		}
-		op2, l2, err := p.evalConstExpr(in[:l-l1])
+		op1, l1, err := p.evalConstExpr(in[:l-l2])
 		if err != nil {
 			return nil, 0, err
 		}
@@ -164,6 +164,8 @@ func constValue(c constant.Value) any {
 	return nil
 }
 
+// Correspondence between language independent parscan tokens and Go stdlib tokens,
+// To enable the use of the Go constant expression evaluator.
 var gotok = map[lang.Token]token.Token{
 	lang.Char:         token.CHAR,
 	lang.Imag:         token.IMAG,
@@ -352,13 +354,12 @@ func (p *Parser) parseVarLine(in Tokens) (out Tokens, err error) {
 		values = nil
 	}
 	for i, v := range values {
-		if v, err = p.parseExpr(v); err != nil {
+		if v, err = p.parseExpr(v, ""); err != nil {
 			return out, err
 		}
+		out = append(out, scanner.Token{Tok: lang.Ident, Str: vars[i]})
 		out = append(out, v...)
-		out = append(out,
-			scanner.Token{Tok: lang.Ident, Str: vars[i]},
-			scanner.Token{Tok: lang.Assign})
+		out = append(out, scanner.Token{Tok: lang.Assign})
 	}
 	return out, err
 }