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// Copyright (c) 2020-2024 Tesla (Yinsen) Zhang.
// Use of this source code is governed by the MIT license that can be found in the LICENSE.md file.
package org.aya.tyck.ctx;

import kala.collection.mutable.MutableLinkedHashMap;
import kala.control.Option;
import org.aya.syntax.core.Jdg;
import org.aya.syntax.ref.LocalVar;
import org.aya.util.Scoped;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

/**
 * A locally, lazy substitution

 * Every substitution should be well-scoped, i.e.,
 * {@link Jdg} can only refer to some free variable or elder lazy substitution.
 */
public record LocalLet(
  @Override @Nullable LocalLet parent,
  @NotNull MutableLinkedHashMap subst
) implements Scoped {
  public LocalLet() { this(null, MutableLinkedHashMap.of()); }
  @Override public @NotNull LocalLet self() { return this; }

  @Override public @NotNull LocalLet derive() {
    return new LocalLet(this, MutableLinkedHashMap.of());
  }

  @Override public @NotNull Option getLocal(@NotNull LocalVar key) {
    return subst.getOption(key);
  }

  @Override public void putLocal(@NotNull LocalVar key, @NotNull Jdg value) { subst.put(key, value); }
}