HOL-master/examples/lassie/sempre/src/edu/stanford/nlp/sempre/SemType.java
package edu.stanford.nlp.sempre;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonValue;

import fig.basic.LispTree;

import java.util.*;

/**
 * A simple type system for Formulas.  SemType represents a union over base
 * types, where each base type is either
 *   - entity type, or
 *   - entity type -> base type Example of a 0-ary (for booleans) (type bool)
 *
 * Example of a unary (for Obama)
 *   (union fb:government.politician fb:government.us_president ...)
 *
 * Example of a binary (for born in) [remember, arg1 is the argument, arg0 is
 * the return type]
 *   (-> fb:location.location fb:people.person)
 *
 * Note: type equality is not implemented, since it's better to use meet() to
 * exploit the finer lattice structure of the type system.
 *
 * @author Percy Liang
 */
public abstract class SemType {
  // Return whether the type is valid (not bottom).
  public abstract boolean isValid();

  // Return the meet of |this| and |that|.
  public abstract SemType meet(SemType that);

  // Return the reversed type for functions: (s -> t) to (t -> s)
  public abstract SemType reverse();

  // Treat |this| as a function type and apply it to the argument |that|.
  // This is just an internal function.
  public abstract SemType apply(SemType that);

  // These are really the primitives.
  public SemType getArgType() { return reverse().apply(SemType.topType); }
  public SemType getRetType() { return apply(SemType.topType); }

  public abstract LispTree toLispTree();

  @JsonValue
  @Override
  public String toString() { return toLispTree().toString(); }

  @JsonCreator
  public static SemType fromString(String s) {
    return fromLispTree(LispTree.proto.parseFromString(s));
  }

  public static SemType fromLispTree(LispTree tree) {
    if (tree.isLeaf()) {
      if (tree.value.equals("top")) return topType;
      return new AtomicSemType(tree.value);
    }
    if ("union".equals(tree.child(0).value)) {
      List<SemType> result = new ArrayList<>();
      for (int i = 1; i < tree.children.size(); i++)
        result.add(fromLispTree(tree.child(i)));
      return new UnionSemType(result);
    }
    if ("->".equals(tree.child(0).value)) {
      SemType result = fromLispTree(tree.child(tree.children.size() - 1));
      for (int i = tree.children.size() - 2; i >= 1; i--)
        result = new FuncSemType(fromLispTree(tree.child(i)), result);
      return result;
    }
    throw new RuntimeException("Invalid type: " + tree);
  }

  // Create a new instance of SemType from type names (Strings)

  public static SemType newAtomicSemType(String type) {
    return new AtomicSemType(type);
  }

  public static SemType newFuncSemType(String argType, String retType) {
    return new FuncSemType(argType, retType);
  }

  public static SemType newUnionSemType(Collection<String> types) {
    List<SemType> t = new ArrayList<>();
    for (String x : types)
      t.add(new AtomicSemType(x));
    return new UnionSemType(t).simplify();
  }

  public static SemType newUnionSemType(String... types) {
    return newUnionSemType(Arrays.asList(types));
  }

  // Common types
  public static final SemType topType = new TopSemType();
  public static final SemType bottomType = new UnionSemType();
  public static final SemType stringType = new AtomicSemType(CanonicalNames.TEXT);
  public static final SemType intType = new AtomicSemType(CanonicalNames.INT);
  public static final SemType floatType = new AtomicSemType(CanonicalNames.FLOAT);
  public static final SemType dateType = new AtomicSemType(CanonicalNames.DATE);
  public static final SemType timeType = new AtomicSemType(CanonicalNames.TIME);
  public static final SemType numberType = new AtomicSemType(CanonicalNames.NUMBER);
  public static final SemType numberOrDateType = new UnionSemType(numberType, dateType);
  public static final SemType entityType = new AtomicSemType(CanonicalNames.ENTITY);
  public static final SemType anyType = new AtomicSemType(CanonicalNames.ANY);

  public static final FuncSemType topTopFunc = new FuncSemType(topType, topType);
  public static final FuncSemType anyAnyFunc = new FuncSemType(anyType, anyType);
  public static final FuncSemType compareFunc = new FuncSemType(numberOrDateType, numberOrDateType);
}
