scanner: exponent without sign

vlib/compiler/scanner.v

@@ -213,8 +213,13 @@ fn (s mut Scanner) ident_dec_number() string {
 	}
 	// scan exponential part
 	mut has_exponential_part := false
-	if s.expect('e+', s.pos) || s.expect('e-', s.pos) {
+	if s.expect('e', s.pos) || s.expect('E', s.pos) {
-		exp_start_pos := s.pos += 2
+		exp_start_pos := (s.pos++)
+
+		if s.text[s.pos] in [`-`, `+`] {
+			s.pos++
+		}
+
 		for s.pos < s.text.len && s.text[s.pos].is_digit() {
 			s.pos++
 		}

vlib/v/scanner/scanner.v

@@ -208,8 +208,13 @@ fn (s mut Scanner) ident_dec_number() string {
 	}
 	// scan exponential part
 	mut has_exponential_part := false
-	if s.expect('e+', s.pos) || s.expect('e-', s.pos) {
+	if s.expect('e', s.pos) || s.expect('E', s.pos) {
-		exp_start_pos := s.pos += 2
+		exp_start_pos := (s.pos++)
+
+		if s.text[s.pos] in [`-`, `+`] {
+			s.pos++
+		}
+
 		for s.pos < s.text.len && s.text[s.pos].is_digit() {
 			s.pos++
 		}

vlib/v/scanner/scanner_test.v

@@ -33,7 +33,16 @@ fn test_scan() {
 	assert c == 9
 	c = 1_000_000
 	assert c == 1000000
+	
+	// test float conversion and reading
 	d := f64(23_000_000e-3)
 	assert int(d) == 23000 
+	mut e := f64(1.2E3) * f64(-1e-1)
+	assert e == -120.0
+	e = f64(1.2E3) * f64(1e-1)
+	assert e == 120.0
+	assert 1.23e+10 == 1.23e10
+	assert 1.23e+10 == 1.23e0010
+	assert -1.23e+10 == 1.23e0010*-1.0
 }