-- in.cue --
a1: {
    f: [f]
}

a2: {
    f: f
}

a3: {
    f: { g: f }
}

a4: {
    a: [a|int]
}

a5: {
    a: b: a | int
}

a6: {
    a: a | int
}

b1: {
    b: a & [1]
    a: [a|int]
}

b2: {
    a: [a|int]
    b: a & [1]
}

b3: {
    x: a: [a|int]
    b: x & {a: [1]}
}

b4: {
    b: x.y & [1]
    x: y: [y]
}

b5: {
    b: x.y & {a: [1]}
    x: y: a: [a|int]
}

b6: {
    b: x & {a: [1]}
    x: a: [a]
}

// TODO: erroneous: b should be an error. My suspicion is that `a` is detected
// as a reference cycle, because list don't introduce a new scope, allowing
// `1` to unify with the equivalent of `a: a` (which normally would be okay).
b7: {
    b: a & [[1]]
    a: [a]
}

c1: {
  a: {
    b: {}
    c: a & b
  }
}

// indirection
d1: {
    a: b: c: d: { h: int, t: r }
    r: a.b

    x: a.b.c
}

d2: {
    x: a.b.c

    r: a.b
    a: b: c: d: { h: int, t: r }
}

d3: {
    config: {
        a: b: c: indirect
        indirect: [a.b, null][i]
        i: int | *1
    }
    x: config & { i: 0 }
}


// combining structural with reference cycles
e1: {
    a: a
    a: c: a

    b: c: b
    b: b
}

e2: {
    a: {a}
    a: c: a

    b: c: b
    b: {b}
}

e3: {
    a: [a]
    a: c: a

    b: [b]
    b: c: b
}

e4: {
    a: [a | {}]
    a: [[{c: 1}]]

    b: [[{c: 1}]]
    b: [b | {}]
}


e5: {
    a: c: a | int
    a: a | int

    b: b | int
    b: c: b | int
}


// validating values
v1: {
    x: [x | int, 1]
    y: x & [[[2], 1], 1]
}

v2: {
    y: x & [[[2], 1], 1]
    x: [x | int, 1]
}

v3: {
    list: {
        head: int
        tail: list | null
    }

    myList: list
    myList: {
        head: 2
        tail: {
            head: 3
            tail: {
                head: 4
            }
        }
    }
}

v4: {
    list: {
        head: int
        tail: list | 1
    }

    myList: list
    myList: {
        head: 2
        tail: head: 3
    }
}

v5: {
    list: {
        head: int
        tail: list | {}
    }

    myList: list
    myList: {
        head: 2
        tail: head: 3
    }
}


// Example from "The Logic of Type Feature Structures" (Bob Carpenter)/
z1: {
    y: {
        f: h: g
        g: _
    }
    x: {
        f: _
        g: f
    }
    z: x & y
}


// Ensure these are NOT treated as structural errors.

n1: a: b: int
n2: n1 & { a: n1 }
n3: n1 & { n1 }
n4: n1 & { x: n1 & { y: n1 & { z: int }}}


-- out/eval --
Errors:
a1.f.0: structural cycle
a3.f.g: structural cycle
b4.x.y.0: structural cycle
b6.b.a.0: conflicting types list and int
b6.b.a.0.0: structural cycle
b6.x.a.0: structural cycle
b7.a.0: structural cycle
c1.a.c.c: structural cycle
d1.a.b.c.d.t: structural cycle
d1.r: structural cycle
d2.a.b.c.d.t: structural cycle
d3.x.a.b.c: structural cycle
d3.x.indirect: structural cycle
e1.a.c: structural cycle
e1.b.c: structural cycle
e2.a.c: structural cycle
e2.b.c: structural cycle
e3.a: conflicting types list and struct
e3.a.0: conflicting types list and struct
e3.a.0: structural cycle
e3.a.c: conflicting types list and struct
e3.a.c: structural cycle
e3.b: conflicting types list and struct
e3.b.0: conflicting types list and struct
e3.b.0: structural cycle
e3.b.c: conflicting types list and struct
e3.b.c: structural cycle
z1.z.f.h.h: structural cycle
z1.z.g.h: structural cycle
b4.x.y.0: structural cycle:
    ./in.cue:41:8
d2.a.b.c.d.t: structural cycle:
    ./in.cue:79:8
d2.r: structural cycle:
    ./in.cue:79:8

Result:
(_|_){
  // [eval]
  a1: (_|_){
    // [structural cycle]
    f: (_|_){
      // [structural cycle]
      0: (_|_){
        // [structural cycle] a1.f.0: structural cycle
        0: (_|_){// 〈0;f〉
        }
      }
    }
  }
  a2: (struct){
    f: (_){ _ }
  }
  a3: (_|_){
    // [structural cycle]
    f: (_|_){
      // [structural cycle]
      g: (_|_){
        // [structural cycle] a3.f.g: structural cycle
        g: (_|_){// 〈1;f〉
        }
      }
    }
  }
  a4: (struct){
    a: (#list){
      0: (int){ int }
    }
  }
  a5: (struct){
    a: (struct){
      b: (int){ int }
    }
  }
  a6: (struct){
    a: (_){ |((_){ _ }, (int){ int }) }
  }
  b1: (struct){
    b: (#list){
      0: (int){ 1 }
    }
    a: (#list){
      0: (int){ int }
    }
  }
  b2: (struct){
    a: (#list){
      0: (int){ int }
    }
    b: (#list){
      0: (int){ 1 }
    }
  }
  b3: (struct){
    x: (struct){
      a: (#list){
        0: (int){ int }
      }
    }
    b: (struct){
      a: (#list){
        0: (int){ 1 }
      }
    }
  }
  b4: (_|_){
    // [structural cycle]
    b: (_|_){
      // [structural cycle] b4.x.y.0: structural cycle:
      //     ./in.cue:41:8
      0: (int){ 1 }
    }
    x: (_|_){
      // [structural cycle]
      y: (_|_){
        // [structural cycle]
        0: (_|_){
          // [structural cycle] b4.x.y.0: structural cycle
          0: (_|_){// 〈0;y〉
          }
        }
      }
    }
  }
  b5: (struct){
    b: (struct){
      a: (#list){
        0: (int){ 1 }
      }
    }
    x: (struct){
      y: (struct){
        a: (#list){
          0: (int){ int }
        }
      }
    }
  }
  b6: (_|_){
    // [eval]
    b: (_|_){
      // [eval]
      a: (_|_){
        // [eval]
        0: (_|_){
          // [eval] b6.b.a.0: conflicting types list and int
          0: (_|_){
            // [structural cycle] b6.b.a.0.0: structural cycle
          }
        }
      }
    }
    x: (_|_){
      // [structural cycle]
      a: (_|_){
        // [structural cycle]
        0: (_|_){
          // [structural cycle] b6.x.a.0: structural cycle
          0: (_|_){// 〈0;a〉
          }
        }
      }
    }
  }
  b7: (_|_){
    // [structural cycle]
    b: (#list){
      0: (#list){
        0: (int){ 1 }
      }
    }
    a: (_|_){
      // [structural cycle]
      0: (_|_){
        // [structural cycle] b7.a.0: structural cycle
        0: (_|_){// 〈0;a〉
        }
      }
    }
  }
  c1: (_|_){
    // [structural cycle]
    a: (_|_){
      // [structural cycle]
      b: (struct){
      }
      c: (_|_){
        // [structural cycle]
        b: (struct){
        }
        c: (_|_){
          // [structural cycle] c1.a.c.c: structural cycle
          b: (_|_){// {}
          }
          c: (_|_){// (〈1;a〉 & 〈0;b〉)
          }
        }
      }
    }
  }
  d1: (_|_){
    // [structural cycle]
    a: (_|_){
      // [structural cycle]
      b: (_|_){
        // [structural cycle]
        c: (_|_){
          // [structural cycle]
          d: (_|_){
            // [structural cycle]
            h: (int){ int }
            t: (_|_){
              // [structural cycle] d1.a.b.c.d.t: structural cycle
              c: (_|_){// {
                //   d: {
                //     h: int
                //     t: 〈4;r〉
                //   }
                // }
              }
            }
          }
        }
      }
    }
    r: (_|_){
      // [structural cycle] d1.r: structural cycle
      c: (_|_){// {
        //   d: {
        //     h: int
        //     t: 〈4;r〉
        //   }
        // }
      }
    }
    x: (_|_){
      // [structural cycle] d1.a.b.c.d.t: structural cycle
    }
  }
  d2: (_|_){
    // [structural cycle]
    x: (_|_){
      // [structural cycle] d2.a.b.c.d.t: structural cycle:
      //     ./in.cue:79:8
    }
    r: (_|_){
      // [structural cycle] d2.r: structural cycle:
      //     ./in.cue:79:8
      c: (_|_){// {
        //   d: {
        //     h: int
        //     t: 〈4;r〉
        //   }
        // }
      }
    }
    a: (_|_){
      // [structural cycle]
      b: (_|_){
        // [structural cycle]
        c: (_|_){
          // [structural cycle]
          d: (_|_){
            // [structural cycle]
            h: (int){ int }
            t: (_|_){
              // [structural cycle] d2.a.b.c.d.t: structural cycle
              c: (_|_){// {
                //   d: {
                //     h: int
                //     t: 〈4;r〉
                //   }
                // }
              }
            }
          }
        }
      }
    }
  }
  d3: (_|_){
    // [structural cycle]
    config: (struct){
      a: (struct){
        b: (struct){
          c: (null){ null }
        }
      }
      indirect: (null){ null }
      i: (int){ 1 }
    }
    x: (_|_){
      // [structural cycle]
      a: (_|_){
        // [structural cycle]
        b: (_|_){
          // [structural cycle]
          c: (_|_){
            // [structural cycle] d3.x.a.b.c: structural cycle
            c: (_|_){// 〈2;indirect〉
            }
          }
        }
      }
      indirect: (_|_){
        // [structural cycle] d3.x.indirect: structural cycle
        c: (_|_){// 〈2;indirect〉
        }
      }
      i: (int){ 0 }
    }
  }
  e1: (_|_){
    // [structural cycle]
    a: (_|_){
      // [structural cycle]
      c: (_|_){
        // [structural cycle] e1.a.c: structural cycle
        c: (_|_){// 〈1;a〉
        }
      }
    }
    b: (_|_){
      // [structural cycle]
      c: (_|_){
        // [structural cycle] e1.b.c: structural cycle
        c: (_|_){// 〈1;b〉
        }
      }
    }
  }
  e2: (_|_){
    // [structural cycle]
    a: (_|_){
      // [structural cycle]
      c: (_|_){
        // [structural cycle] e2.a.c: structural cycle
        c: (_|_){// 〈1;a〉
        }
      }
    }
    b: (_|_){
      // [structural cycle]
      c: (_|_){
        // [structural cycle] e2.b.c: structural cycle
        c: (_|_){// 〈1;b〉
        }
      }
    }
  }
  e3: (_|_){
    // [eval]
    a: (_|_){
      // [eval] e3.a: conflicting types list and struct
      c: (_|_){
        // [eval] e3.a.c: conflicting types list and struct
        // e3.a.c: structural cycle
        c: (_|_){// 〈1;a〉
        }
        0: (_|_){// 〈0;a〉
        }
      }
      0: (_|_){
        // [eval] e3.a.0: conflicting types list and struct
        // e3.a.0: structural cycle
        c: (_|_){// 〈1;a〉
        }
        0: (_|_){// 〈0;a〉
        }
      }
    }
    b: (_|_){
      // [eval] e3.b: conflicting types list and struct
      c: (_|_){
        // [eval] e3.b.c: conflicting types list and struct
        // e3.b.c: structural cycle
        c: (_|_){// 〈1;b〉
        }
        0: (_|_){// 〈0;b〉
        }
      }
      0: (_|_){
        // [eval] e3.b.0: conflicting types list and struct
        // e3.b.0: structural cycle
        c: (_|_){// 〈1;b〉
        }
        0: (_|_){// 〈0;b〉
        }
      }
    }
  }
  e4: (struct){
    a: (#list){
      0: (#list){
        0: (struct){
          c: (int){ 1 }
        }
      }
    }
    b: (#list){
      0: (#list){
        0: (struct){
          c: (int){ 1 }
        }
      }
    }
  }
  e5: (struct){
    a: (struct){
      c: (int){ int }
    }
    b: (struct){
      c: (int){ int }
    }
  }
  v1: (struct){
    x: (#list){
      0: (int){ int }
      1: (int){ 1 }
    }
    y: (#list){
      0: (#list){
        0: (#list){
          0: (int){ 2 }
        }
        1: (int){ 1 }
      }
      1: (int){ 1 }
    }
  }
  v2: (struct){
    y: (#list){
      0: (#list){
        0: (#list){
          0: (int){ 2 }
        }
        1: (int){ 1 }
      }
      1: (int){ 1 }
    }
    x: (#list){
      0: (int){ int }
      1: (int){ 1 }
    }
  }
  v3: (struct){
    list: (struct){
      head: (int){ int }
      tail: (null){ null }
    }
    myList: (struct){
      head: (int){ 2 }
      tail: (struct){
        head: (int){ 3 }
        tail: (struct){
          head: (int){ 4 }
          tail: (null){ null }
        }
      }
    }
  }
  v4: (struct){
    list: (struct){
      head: (int){ int }
      tail: (int){ 1 }
    }
    myList: (struct){
      head: (int){ 2 }
      tail: (struct){
        head: (int){ 3 }
        tail: (int){ 1 }
      }
    }
  }
  v5: (struct){
    list: (struct){
      head: (int){ int }
      tail: (struct){
      }
    }
    myList: (struct){
      head: (int){ 2 }
      tail: (struct){ |((struct){
          head: (int){ 3 }
          tail: (struct){
          }
        }, (struct){
          head: (int){ 3 }
        }) }
    }
  }
  z1: (_|_){
    // [structural cycle]
    y: (struct){
      f: (struct){
        h: (_){ _ }
      }
      g: (_){ _ }
    }
    x: (struct){
      f: (_){ _ }
      g: (_){ _ }
    }
    z: (_|_){
      // [structural cycle]
      f: (_|_){
        // [structural cycle]
        h: (_|_){
          // [structural cycle]
          h: (_|_){
            // [structural cycle] z1.z.f.h.h: structural cycle
            h: (_|_){// 〈1;g〉
            }
          }
        }
      }
      g: (_|_){
        // [structural cycle]
        h: (_|_){
          // [structural cycle] z1.z.g.h: structural cycle
          h: (_|_){// 〈1;g〉
          }
        }
      }
    }
  }
  n1: (struct){
    a: (struct){
      b: (int){ int }
    }
  }
  n2: (struct){
    a: (struct){
      b: (int){ int }
      a: (struct){
        b: (int){ int }
      }
    }
  }
  n3: (struct){
    a: (struct){
      b: (int){ int }
    }
  }
  n4: (struct){
    a: (struct){
      b: (int){ int }
    }
    x: (struct){
      a: (struct){
        b: (int){ int }
      }
      y: (struct){
        a: (struct){
          b: (int){ int }
        }
        z: (int){ int }
      }
    }
  }
}
-- out/compile --
--- in.cue
{
  a1: {
    f: [
      〈0;f〉,
    ]
  }
  a2: {
    f: 〈0;f〉
  }
  a3: {
    f: {
      g: 〈1;f〉
    }
  }
  a4: {
    a: [
      (〈0;a〉|int),
    ]
  }
  a5: {
    a: {
      b: (〈1;a〉|int)
    }
  }
  a6: {
    a: (〈0;a〉|int)
  }
  b1: {
    b: (〈0;a〉 & [
      1,
    ])
    a: [
      (〈0;a〉|int),
    ]
  }
  b2: {
    a: [
      (〈0;a〉|int),
    ]
    b: (〈0;a〉 & [
      1,
    ])
  }
  b3: {
    x: {
      a: [
        (〈0;a〉|int),
      ]
    }
    b: (〈0;x〉 & {
      a: [
        1,
      ]
    })
  }
  b4: {
    b: (〈0;x〉.y & [
      1,
    ])
    x: {
      y: [
        〈0;y〉,
      ]
    }
  }
  b5: {
    b: (〈0;x〉.y & {
      a: [
        1,
      ]
    })
    x: {
      y: {
        a: [
          (〈0;a〉|int),
        ]
      }
    }
  }
  b6: {
    b: (〈0;x〉 & {
      a: [
        1,
      ]
    })
    x: {
      a: [
        〈0;a〉,
      ]
    }
  }
  b7: {
    b: (〈0;a〉 & [
      [
        1,
      ],
    ])
    a: [
      〈0;a〉,
    ]
  }
  c1: {
    a: {
      b: {}
      c: (〈1;a〉 & 〈0;b〉)
    }
  }
  d1: {
    a: {
      b: {
        c: {
          d: {
            h: int
            t: 〈4;r〉
          }
        }
      }
    }
    r: 〈0;a〉.b
    x: 〈0;a〉.b.c
  }
  d2: {
    x: 〈0;a〉.b.c
    r: 〈0;a〉.b
    a: {
      b: {
        c: {
          d: {
            h: int
            t: 〈4;r〉
          }
        }
      }
    }
  }
  d3: {
    config: {
      a: {
        b: {
          c: 〈2;indirect〉
        }
      }
      indirect: [
        〈0;a〉.b,
        null,
      ][〈0;i〉]
      i: (int|*1)
    }
    x: (〈0;config〉 & {
      i: 0
    })
  }
  e1: {
    a: 〈0;a〉
    a: {
      c: 〈1;a〉
    }
    b: {
      c: 〈1;b〉
    }
    b: 〈0;b〉
  }
  e2: {
    a: {
      〈1;a〉
    }
    a: {
      c: 〈1;a〉
    }
    b: {
      c: 〈1;b〉
    }
    b: {
      〈1;b〉
    }
  }
  e3: {
    a: [
      〈0;a〉,
    ]
    a: {
      c: 〈1;a〉
    }
    b: [
      〈0;b〉,
    ]
    b: {
      c: 〈1;b〉
    }
  }
  e4: {
    a: [
      (〈0;a〉|{}),
    ]
    a: [
      [
        {
          c: 1
        },
      ],
    ]
    b: [
      [
        {
          c: 1
        },
      ],
    ]
    b: [
      (〈0;b〉|{}),
    ]
  }
  e5: {
    a: {
      c: (〈1;a〉|int)
    }
    a: (〈0;a〉|int)
    b: (〈0;b〉|int)
    b: {
      c: (〈1;b〉|int)
    }
  }
  v1: {
    x: [
      (〈0;x〉|int),
      1,
    ]
    y: (〈0;x〉 & [
      [
        [
          2,
        ],
        1,
      ],
      1,
    ])
  }
  v2: {
    y: (〈0;x〉 & [
      [
        [
          2,
        ],
        1,
      ],
      1,
    ])
    x: [
      (〈0;x〉|int),
      1,
    ]
  }
  v3: {
    list: {
      head: int
      tail: (〈1;list〉|null)
    }
    myList: 〈0;list〉
    myList: {
      head: 2
      tail: {
        head: 3
        tail: {
          head: 4
        }
      }
    }
  }
  v4: {
    list: {
      head: int
      tail: (〈1;list〉|1)
    }
    myList: 〈0;list〉
    myList: {
      head: 2
      tail: {
        head: 3
      }
    }
  }
  v5: {
    list: {
      head: int
      tail: (〈1;list〉|{})
    }
    myList: 〈0;list〉
    myList: {
      head: 2
      tail: {
        head: 3
      }
    }
  }
  z1: {
    y: {
      f: {
        h: 〈1;g〉
      }
      g: _
    }
    x: {
      f: _
      g: 〈0;f〉
    }
    z: (〈0;x〉 & 〈0;y〉)
  }
  n1: {
    a: {
      b: int
    }
  }
  n2: (〈0;n1〉 & {
    a: 〈1;n1〉
  })
  n3: (〈0;n1〉 & {
    〈1;n1〉
  })
  n4: (〈0;n1〉 & {
    x: (〈1;n1〉 & {
      y: (〈2;n1〉 & {
        z: int
      })
    })
  })
}