"nullary sum" meaning in English

{
  "forms": [
    {
      "form": "nullary sums",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "nullary sum (plural nullary sums)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Arithmetic",
          "orig": "en:Arithmetic",
          "parents": [
            "Applied sciences",
            "Mathematics",
            "Sciences",
            "Formal sciences",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "2012, Robert Harper, Practical Foundations for Programming Languages, page 86",
          "text": "These concepts are expressed by sum types, specifically the binary sum, which offers a choice of two things, and the nullary sum, which offers a choice of no things.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "An empty sum."
      ],
      "id": "en-nullary_sum-en-noun-ODOnFWvW",
      "links": [
        [
          "arithmetic",
          "arithmetic"
        ],
        [
          "empty sum",
          "empty sum"
        ]
      ],
      "raw_glosses": [
        "(arithmetic) An empty sum."
      ],
      "topics": [
        "arithmetic"
      ]
    }
  ],
  "word": "nullary sum"
}

{
  "forms": [
    {
      "form": "nullary sums",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "nullary sum (plural nullary sums)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations",
        "en:Arithmetic"
      ],
      "examples": [
        {
          "ref": "2012, Robert Harper, Practical Foundations for Programming Languages, page 86",
          "text": "These concepts are expressed by sum types, specifically the binary sum, which offers a choice of two things, and the nullary sum, which offers a choice of no things.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "An empty sum."
      ],
      "links": [
        [
          "arithmetic",
          "arithmetic"
        ],
        [
          "empty sum",
          "empty sum"
        ]
      ],
      "raw_glosses": [
        "(arithmetic) An empty sum."
      ],
      "topics": [
        "arithmetic"
      ]
    }
  ],
  "word": "nullary sum"
}