{
  "type": "project",
  "input": {
    "type": "extend",
    "input": {
      "type": "filter",
      "input": {
        "type": "bgp",
        "patterns": [
          {
            "type": "pattern",
            "termType": "Quad",
            "subject": {
              "termType": "Variable",
              "value": "s"
            },
            "predicate": {
              "termType": "NamedNode",
              "value": "http://example.org/str"
            },
            "object": {
              "termType": "Variable",
              "value": "str"
            },
            "graph": {
              "termType": "DefaultGraph",
              "value": ""
            }
          }
        ]
      },
      "expression": {
        "type": "expression",
        "subType": "operator",
        "operator": "langmatches",
        "args": [
          {
            "type": "expression",
            "subType": "operator",
            "operator": "lang",
            "args": [
              {
                "type": "expression",
                "subType": "term",
                "term": {
                  "termType": "Variable",
                  "value": "str"
                }
              }
            ]
          },
          {
            "type": "expression",
            "subType": "term",
            "term": {
              "termType": "Literal",
              "value": "en",
              "datatype": {
                "termType": "NamedNode",
                "value": "http://www.w3.org/2001/XMLSchema#string"
              }
            }
          }
        ]
      }
    },
    "variable": {
      "termType": "Variable",
      "value": "s2"
    },
    "expression": {
      "type": "expression",
      "subType": "operator",
      "operator": "strlang",
      "args": [
        {
          "type": "expression",
          "subType": "operator",
          "operator": "str",
          "args": [
            {
              "type": "expression",
              "subType": "term",
              "term": {
                "termType": "Variable",
                "value": "str"
              }
            }
          ]
        },
        {
          "type": "expression",
          "subType": "term",
          "term": {
            "termType": "Literal",
            "value": "en-US",
            "datatype": {
              "termType": "NamedNode",
              "value": "http://www.w3.org/2001/XMLSchema#string"
            }
          }
        }
      ]
    }
  },
  "variables": [
    {
      "termType": "Variable",
      "value": "s"
    },
    {
      "termType": "Variable",
      "value": "s2"
    }
  ]
}