hako(parser): add index operator support

- ParserExprBox: support postfix [expr] and lower to Method(recv, "get", [index])
- ParserStmtBox: support index assignment IDENT [expr] = expr → Expr(Method(recv, "set", [idx, val]))
- Note: lowering uses existing Method → MIR emit path (int args). Phase‑1 canaries use int indices/values.

lang/src/compiler/parser/expr/parser_expr_box.hako

@@ -168,6 +168,16 @@ static box ParserExprBox {
             k = ctx.skip_ws(src, k)
             if src.substring(k, k+1) == ")" { k = k + 1 }
             node = "{\"type\":\"Method\",\"recv\":" + node + ",\"method\":\"" + mname + "\",\"args\":" + args_json2 + "}"
+          } else if tch == "[" {
+            // Index access: node[ index ] → Method(recv=node, method="get", args=[index])
+            k = k + 1
+            k = ctx.skip_ws(src, k)
+            local idx_json = ctx.parse_expr2(src, k)
+            k = ctx.gpos_get()
+            k = ctx.skip_ws(src, k)
+            if src.substring(k, k+1) == "]" { k = k + 1 }
+            local args_idx = "[" + idx_json + "]"
+            node = "{\\\"type\\\":\\\"Method\\\",\\\"recv\\\":" + node + ",\\\"method\\\":\\\"get\\\",\\\"args\\\":" + args_idx + "}"
           } else {
             cont2 = 0
           }
@@ -352,4 +362,3 @@ static box ParserExprBox {
     return out + "@" + ctx.i2s(j)
   }
 }
-

lang/src/compiler/parser/stmt/parser_stmt_box.hako

@@ -16,13 +16,40 @@ static box ParserStmtBox {
       return me.parse_using(src, j, stmt_start, ctx)
     }
 
-    // assignment: IDENT '=' expr
+    // assignment: IDENT '[' expr ']' '=' expr  or  IDENT '=' expr
     if j < src.size() && ctx.is_alpha(src.substring(j, j+1)) {
       local idp0 = ctx.read_ident2(src, j)
       local at0 = idp0.lastIndexOf("@")
       if at0 > 0 {
         local name0 = idp0.substring(0, at0)
         local k0 = ctx.to_int(idp0.substring(at0+1, idp0.size()))
+        // Case A: index assignment arr[expr] = value
+        {
+          local kA = ctx.skip_ws(src, k0)
+          if kA < src.size() && src.substring(kA, kA+1) == "[" {
+            kA = kA + 1
+            kA = ctx.skip_ws(src, kA)
+            // parse index expression
+            local idx_json = ctx.parse_expr2(src, kA)
+            kA = ctx.gpos_get()
+            kA = ctx.skip_ws(src, kA)
+            if kA < src.size() && src.substring(kA, kA+1) == "]" { kA = kA + 1 }
+            kA = ctx.skip_ws(src, kA)
+            if kA < src.size() && src.substring(kA, kA+1) == "=" {
+              // parse RHS
+              kA = kA + 1
+              kA = ctx.skip_ws(src, kA)
+              local rhs_json = ctx.parse_expr2(src, kA)
+              kA = ctx.gpos_get()
+              // Build Method set(name[idx], rhs) as Expr statement
+              local recv = "{\\\"type\\\":\\\"Var\\\",\\\"name\\\":\"" + name0 + "\"}"
+              local args = "[" + idx_json + "," + rhs_json + "]"
+              local method = "{\\\"type\\\":\\\"Method\\\",\\\"recv\\\":" + recv + ",\\\"method\\\":\\\"set\\\",\\\"args\\\":" + args + "}"
+              ctx.gpos_set(kA)
+              return "{\"type\":\"Expr\",\"expr\":" + method + "}"
+            }
+          }
+        }
         k0 = ctx.skip_ws(src, k0)
         if k0 < src.size() && src.substring(k0, k0+1) == "=" {
           local eq_two = "="
@@ -199,4 +226,3 @@ static box ParserStmtBox {
     return ""
   }
 }
-