# Retriever Modules - Standard Library

> Tactus exposes Biblicus-backed retrievers as Lua modules so you can select a retriever explicitly at the top of your `.tac` file.

Canonical: https://tactus.anth.us/stdlib/retrievers/

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[Standard Library](/stdlib/) / Retriever Modules

# Retriever Modules

- 5 classes

Tactus exposes Biblicus-backed retrievers as Lua modules so you can select a retriever explicitly at the top of your \`.tac\` file.

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Tactus exposes Biblicus-backed retrievers as Lua modules so you can select a retriever explicitly at the top of your `.tac` file.

## Embedding index (file-backed)

```lua
local FilesystemCorpus = require("tactus.corpora.filesystem")
local vector = require("tactus.retrievers.embedding_index_file")

support_notes = FilesystemCorpus.Corpus {
  root = "corpora/support-notes",
  configuration = {
    pipeline = {
      extract = {
        -- extraction steps (optional)
      }
    }
  }
}

support_search = vector.Retriever {
  corpus = support_notes,
  configuration = {
    pipeline = {
      index = {
        embedding_provider = { provider_id = "hash-embedding", dimensions = 64 }
      },
      query = {
        limit = 3,
        maximum_total_characters = 1200
      }
    }
  }
}
```

## Embedding index (in-memory)

```lua
local FilesystemCorpus = require("tactus.corpora.filesystem")
local vector = require("tactus.retrievers.embedding_index_inmemory")

notes = FilesystemCorpus.Corpus {
  root = "corpora/notes",
  configuration = {
    pipeline = {
      extract = {
        -- extraction steps (optional)
      }
    }
  }
}

search = vector.Retriever {
  corpus = notes,
  configuration = {
    pipeline = {
      index = {
        embedding_provider = { provider_id = "hash-embedding", dimensions = 64 },
        maximum_cache_total_items = 5000
      },
      query = {
        limit = 2
      }
    }
  }
}
```

## SQLite full-text search

```lua
local FilesystemCorpus = require("tactus.corpora.filesystem")
local vector = require("tactus.retrievers.sqlite_full_text_search")

notes = FilesystemCorpus.Corpus {
  root = "corpora/notes",
  configuration = {
    pipeline = {
      extract = {
        -- extraction steps (optional)
      }
    }
  }
}

search = vector.Retriever {
  corpus = notes,
  configuration = {
    pipeline = {
      index = {
        snippet_characters = 400,
        chunk_size = 800,
        chunk_overlap = 200
      },
      query = {
        limit = 2,
        maximum_total_characters = 1200
      }
    }
  }
}
```

## TF vector (term-frequency)

```lua
local FilesystemCorpus = require("tactus.corpora.filesystem")
local vector = require("tactus.retrievers.tf_vector")

notes = FilesystemCorpus.Corpus {
  root = "corpora/notes",
  configuration = {
    pipeline = {
      extract = {
        -- extraction steps (optional)
      }
    }
  }
}

search = vector.Retriever {
  corpus = notes,
  configuration = {
    pipeline = {
      index = {
        -- optional index settings
      },
      query = {
        limit = 2,
        maximum_total_characters = 1200
      }
    }
  }
}
```

## Classes

- [Base](https://github.com/AnthusAI/Tactus/tree/main/tactus/stdlib/tac/tactus/retrievers/base.tac) (`base.tac`)
- [Embedding_index_file](https://github.com/AnthusAI/Tactus/tree/main/tactus/stdlib/tac/tactus/retrievers/embedding_index_file.tac) (`embedding_index_file.tac`)
- [Embedding_index_inmemory](https://github.com/AnthusAI/Tactus/tree/main/tactus/stdlib/tac/tactus/retrievers/embedding_index_inmemory.tac) (`embedding_index_inmemory.tac`)
- [Sqlite_full_text_search](https://github.com/AnthusAI/Tactus/tree/main/tactus/stdlib/tac/tactus/retrievers/sqlite_full_text_search.tac) (`sqlite_full_text_search.tac`)
- [Tf_vector](https://github.com/AnthusAI/Tactus/tree/main/tactus/stdlib/tac/tactus/retrievers/tf_vector.tac) (`tf_vector.tac`)

## Quick Start

Load the module:

```lua
local retrievers = require("tactus.retrievers")
```

[View source on GitHub →](https://github.com/AnthusAI/Tactus/tree/main/tactus/stdlib/tac/tactus/retrievers)

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- [*← Previous Module* **Generate Module**](/stdlib/generate/)
- [*Next Module →* **Web Research**](/stdlib/web/)

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## Explore more modules

The standard library includes modules for classification, extraction, generation, and more.

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