Store large items as files

[AshleyYakeley]

Big files are not quickly hashable. So it seems like the best approach is to make files mutable and assign UUIDs to them randomly.

Create a type File, with File <= Entity.

Possibly: create a filetype keyword, like opentype, that would generate subtypes of File.

Possibly: predefined file types for a library of file operations, e.g. image sizes, media durations, etc.

[AshleyYakeley]

File types are like literal types, they need to be pre-defined.

• File
• TextFile
• ImageFile
• VideoFile
• AudioFile

These are somewhat similar to references. We might have TextFile <: TextRef (see #4). But note files are deleteable, and TextRefs might not be.

[AshleyYakeley]

TextFile <: File <: Entity
TextFile <: TextRef

[AshleyYakeley]

Can we do File a <: a? File would be covariant.

Probably not, due to confluence. When the solver has the constraint File a <: File b, it's not clear whether to reduce that to a <: b (per covariance) or a <: File b.

[AshleyYakeley]

Note that the type of a file does not imply an encoding. Text can be stored as utf8 or uft16 or whatever. Images can be stored as PNG or JPEG, etc.

[AshleyYakeley]

UTF8File <: File <: Entity
UTF8File <: WholeRef Text

(files can't do insert/delete like TextRef)

PNGFile <: File <: Entity
PNGFile <: ImageRef

[AshleyYakeley]

File API:

File <: Entity;
fileSize: File -> Action Integer;
deleteFile: File -> Action ();
newFile @T: Action T; # T is a "file type"

Format API:

UTF8File <: File;
UTF8File <: WholeRef Text;
PNGFile <: File;
PNGFile <: WholeRef Image;
JPEGFile <: File;
JPEGFile <: WholeRef (Integer, Metadata, Image); # quality factor

or

ImageFile <: File;
ImageFile <: WholeRef (ImageFileType, Metadata, Image);

or

utf8File: File -> WholeRef Text;
pngFile: File -> WholeRef Image;

[AshleyYakeley]

Not seeing a pressing need for this, for the moment.

[AshleyYakeley]

type File {-p,+q};
subtype File {-p,+q} <: WholeModel {-p,+q};

This is definitely wrong. The whole point of files is that they may be too big to be WholeModels.

[AshleyYakeley]

raw interface:

opentype FileEntity;
model.FileEntity: Storage -> FileEntity -> BlobModel;

• requires BlobModel type #283

[AshleyYakeley]

Would like to record the type of the file. For each type T, we need a function from BlobModel to T.

filetype F of T = p;
p: BlobModel -> T;
# F is open entity type
model.File @F: Storage -> F -> T