sdf-wit 0.14.0

package sdf:df;

interface types {

  use sdf:arrow/types.{ dtype, dvalue as lit};

  type index = u16;

  type expressions = list<expr>;

  // list of expr node based on https://datafusion.apache.org/user-guide/expressions.html
  variant operation {
    filter(expressions)
  }

  // content of the each AST
  variant expr {
    binary(binary-exp),
    col(column),
    lit(lit),
  }

  record binary-exp {
    operator: operator,
    left: index,
    right: index
  }

  variant operator {
      plus,
      minus,
      lt-eq,
      eq,
      gt
  }

  record column {
    name: string
  }

  record sort-options {
    descending: list<bool>,
    maintain-order: bool,
  }

  record column-names {
    names: list<string>
  }

  record column-schema {
    name: string,
    index: u8,
    schema: dtype
  }
}

interface lazy {

  use types.{ index, expressions, binary-exp, operator, column, operation, lit, sort-options, column-names, dtype, column-schema };

  // presents data frame as resource
  resource df-value {
      // find: static func(name: string) -> option<df-value>;
      run: func(ops: operation) -> result<df-value, string>;
      select: func(columns: column-names) -> result<df-value,string>;
      sort: func(columns: column-names, options: sort-options) -> result<df-value,string>;
      shape: func() -> tuple<u64,u64>;
      schema: func(columns: column-names) -> result<list<column-schema>,string>;
      rows: func() -> result<row-value,string>;
      sql: func(sql: string) -> result<df-value,string>;
      head: func(rows: u64) -> result<df-value,string>;
      name: func() -> string;
  }

  resource row-value {
      end: func() -> bool;
      next: func() -> bool;
      index: func() -> s64;
      skip: func(row: s64) -> bool;
      value: func(col: u8) -> option<lit>;
  }
}

world arrow-world {
  import lazy;
}