From 746655c1d541487724288d83059291143ecb0fbb Mon Sep 17 00:00:00 2001
From: joe-conigliaro <joe-conigliaro@users.noreply.github.com>
Date: Wed, 25 Sep 2019 21:53:44 +1000
Subject: [PATCH] compiler: re assignable blank identifier `_` & no longer a
 variable

---
 compiler/gen_c.v  | 28 ++++++++++++++++++++++++++++
 compiler/gen_js.v |  9 +++++++++
 compiler/parser.v | 29 +++++++++++++++++++++--------
 3 files changed, 58 insertions(+), 8 deletions(-)

diff --git a/compiler/gen_c.v b/compiler/gen_c.v
index 0a97577912..7b054e0809 100644
--- a/compiler/gen_c.v
+++ b/compiler/gen_c.v
@@ -68,6 +68,34 @@ fn (p mut Parser) gen_fn_decl(f Fn, typ, str_args string) {
 	p.genln('$dll_export_linkage$typ $fn_name_cgen($str_args) {')
 }
 
+// blank identifer assignment `_ = 111` 
+fn (p mut Parser) gen_blank_identifier_assign() {
+	p.next()
+	p.check(.assign)
+	pos := p.cgen.add_placeholder()
+	mut typ := p.bool_expression()
+	tmp := p.get_tmp()
+	// handle or
+	if p.tok == .key_orelse {
+		p.cgen.set_placeholder(pos, '$typ $tmp = ')
+		p.genln(';')
+		typ = typ.replace('Option_', '')
+		p.next()
+		p.check(.lcbr)
+		p.genln('if (!$tmp .ok) {')
+		p.register_var(Var {
+			name: 'err'
+			typ: 'string'
+			is_mut: false
+			is_used: true
+		})
+		p.genln('string err = $tmp . error;')
+		p.statements()
+		p.returns = false
+	}
+	p.gen(';')
+}
+
 fn types_to_c(types []Type, table &Table) string {
 	mut sb := strings.new_builder(10)
 	for t in types {
diff --git a/compiler/gen_js.v b/compiler/gen_js.v
index 7b42f6945c..a3bf9235ef 100644
--- a/compiler/gen_js.v
+++ b/compiler/gen_js.v
@@ -33,6 +33,15 @@ fn (p mut Parser) gen_fn_decl(f Fn, typ, _str_args string) {
 	}
 }
 
+fn (p mut Parser) gen_blank_identifier_assign() {
+	typ := p.bool_expression()
+	or_else := p.tok == .key_orelse
+	//tmp := p.get_tmp()
+	if or_else {
+		//panic('optionals todo')
+	}
+}
+
 fn types_to_c(types []Type, table &Table) string {
 	mut sb := strings.new_builder(10)
 	for t in types {
diff --git a/compiler/parser.v b/compiler/parser.v
index 4782ee22f2..49da5664e8 100644
--- a/compiler/parser.v
+++ b/compiler/parser.v
@@ -1196,6 +1196,10 @@ fn (p mut Parser) statement(add_semi bool) string {
 			//p.log('var decl')
 			p.var_decl()
 		}
+		// `_ = 777`
+		else if p.lit == '_' && p.peek() == .assign {
+			p.gen_blank_identifier_assign()
+		}
 		else {
 			// panic and exit count as returns since they stop the function
 			if p.lit == 'panic' || p.lit == 'exit' {
@@ -1373,15 +1377,13 @@ fn (p mut Parser) var_decl() {
 		types = t.replace('_V_MulRet_', '').replace('_PTR_', '*').split('_V_')
 	}
 	for i, name in names {
-		typ := types[i]
-		if names.len > 1 {
-			if names.len != types.len {
-				mr_fn := p.cgen.cur_line.find_between('=', '(').trim_space()
-				p.error('assignment mismatch: ${names.len} variables but `$mr_fn` returns $types.len values.')
-			}
-			p.gen(';\n')
-			p.gen('$typ $name = ${mr_var_name}.var_$i')
+		if name == '_' {
+			// if names.len == 1 {
+			// 	p.error('no new variables on left side of :=')
+			// }
+			continue
 		}
+		typ := types[i]
 		// println('var decl tok=${p.strtok()} ismut=$is_mut')
 		var_scanner_pos := p.scanner.get_scanner_pos()
 		// name := p.check_name()
@@ -1395,6 +1397,14 @@ fn (p mut Parser) var_decl() {
 		if name.len > 1 && contains_capital(name) {
 			p.error('variable names cannot contain uppercase letters, use snake_case instead')
 		}
+		if names.len > 1 {
+			if names.len != types.len {
+				mr_fn := p.cgen.cur_line.find_between('=', '(').trim_space()
+				p.error('assignment mismatch: ${names.len} variables but `$mr_fn` returns $types.len values.')
+			}
+			p.gen(';\n')
+			p.gen('$typ $name = ${mr_var_name}.var_$i')
+		}
 		// p.check_space(.decl_assign) // :=
 		// typ := p.gen_var_decl(name, is_static)
 		p.register_var(Var {
@@ -1588,6 +1598,9 @@ fn (p mut Parser) name_expr() string {
 	}
 	// Variable
 	for { // TODO remove
+	if name == '_' {
+		p.error('cannot use `_` as value.')
+	}
 	mut v := p.find_var_check_new_var(name) or { break }
 	if ptr {
 		p.gen('& /*v*/ ')