parser: simplify finishAssignment, add StarEqual support

examples/hello.v

@@ -58,6 +58,8 @@ fn main(a int) int {
 	// those should yield the same ast
 	str.len = str.len + 1
 	str.len += 1
+	str.len -= 1
+	str.len *= 1
 }
 
 fn (v Typ) voidfunc() {}

src/parser.zig

@@ -702,7 +702,7 @@ pub const Parser = struct {
         var expr = try self.parseOr();
 
         if (self.compareAnyOf(&[_]TokenType{
-            .ColonEqual, .Equal, .PlusEqual, .MinusEqual,
+            .ColonEqual, .Equal, .PlusEqual, .MinusEqual, .StarEqual,
         })) {
             return try self.finishAssignment(expr, mutable);
         }
@@ -718,22 +718,33 @@ pub const Parser = struct {
         // TODO convert binary's op field from Token to
         // something else, maybe enum'd
 
+        const new_op_ttype: TokenType = switch (op.ttype) {
+            .ColonEqual => TokenType.ColonEqual,
+            .Equal => .Equal,
+
+            .PlusEqual => .Plus,
+            .MinusEqual => .Minus,
+            .StarEqual => .Star,
+            else => unreachable,
+        };
+
+        const new_lexeme: []const u8 = switch (op.ttype) {
+            .ColonEqual => ":=",
+            .Equal => "=",
+            .PlusEqual => "+",
+            .MinusEqual => "-",
+            .StarEqual => "*",
+            else => unreachable,
+        };
+
         switch (expr.*) {
             .Variable => {
                 switch (op.ttype) {
                     .ColonEqual => return try self.mkVarDecl(expr.Variable, value, mutable),
                     .Equal => return try self.mkAssign(expr.Variable, value),
 
-                    .PlusEqual => {
-                        var plus_op = try self.mkToken(.Plus, "+", op.line);
-                        return try self.mkAssign(
-                            expr.Variable,
-                            try self.mkBinary(expr, plus_op, value),
-                        );
-                    },
-
-                    .MinusEqual => {
-                        var new_op = try self.mkToken(.Minus, "-", op.line);
+                    .PlusEqual, .MinusEqual, .StarEqual => {
+                        var new_op = try self.mkToken(new_op_ttype, new_lexeme, op.line);
                         return try self.mkAssign(
                             expr.Variable,
                             try self.mkBinary(expr, new_op, value),
@@ -751,17 +762,8 @@ pub const Parser = struct {
                         return Result.CompileError;
                     },
 
-                    .PlusEqual => {
-                        var new_op = try self.mkToken(.Plus, "+", op.line);
-                        return try self.mkSet(
-                            get.struc,
-                            get.name,
-                            try self.mkBinary(expr, new_op, value),
-                        );
-                    },
-
-                    .MinusEqual => {
-                        var new_op = try self.mkToken(.Minus, "-", op.line);
+                    .PlusEqual, .MinusEqual, .StarEqual => {
+                        var new_op = try self.mkToken(new_op_ttype, new_lexeme, op.line);
                         return try self.mkSet(
                             get.struc,
                             get.name,

src/scanner.zig

@@ -295,11 +295,11 @@ pub const Scanner = struct {
             '?' => self.makeToken(.QuestionMark),
             '$' => self.makeToken(.DollarSign),
 
-            '-' => self.makeToken(.Minus),
-            '*' => self.makeToken(.Star),
             '%' => self.makeToken(.Modulo),
 
             ':' => self.makeMatchToken('=', .ColonEqual, .Colon),
+            '*' => self.makeMatchToken('=', .StarEqual, .Star),
+            '-' => self.makeMatchToken('=', .MinusEqual, .Minus),
 
             // we use the existing .And and .Or tokens
             // representing the and and or keywords to

src/tokens.zig

@@ -30,6 +30,7 @@ pub const TokenType = enum {
     PlusEqual,
     MinusEqual,
     ColonEqual,
+    StarEqual,
 
     // comparison ones
     EqualEqual,