optimize a in [1,2,3] to a == 1 || a == 2 || a == 3

compiler/optimization.v

@@ -0,0 +1,40 @@
+module main
+
+// `a in [1,2,3]` => `a == 1 || a == 2 || a == 3`
+// avoid allocation
+// `typ` is the type of `a`
+// `ph` is for string_eq()
+fn (p mut Parser) in_optimization(typ string, ph int) {
+	p.check(.lsbr)
+	mut i := 0
+	// Get `a` expr value (can be a string literal, not a variable)
+	expr := p.cgen.cur_line.right(ph)
+	is_str := typ == 'string'
+	//println('!! $p.expr_var.name => $name ($typ)')
+	for p.tok != .rsbr && p.tok != .eof {
+		if i > 0 {
+			if is_str {
+				p.gen(' || string_eq($expr, ')
+			}	else {
+				p.gen(' || $expr == ')
+			}
+		}	
+		if i == 0 {
+			if is_str {
+				p.cgen.set_placeholder(ph, ' string_eq(')
+				p.gen(', ')
+			} else {
+				p.gen(' ==')
+			}	
+		}	
+		p.check_types(p.bool_expression(), typ)
+		if is_str {
+			p.gen(')')
+		}	
+		if p.tok != .rsbr {
+			p.check(.comma)
+		}
+		i++
+	}	
+	p.check(.rsbr)
+}