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Types in the Oils Runtime - OSH and YSH

Here are all types of values in the Oils runtime, organized for understanding.

Eight Atoms

Values of these types are immutable:

• Null
• Str Int Float - data types
• Range - iteration over 3 .. 5
• Eggex Match - pattern matching

A type with one value:

• Stdin - used for buffered line I/O in the YSH for loop

The Str type is the only type shared between OSH and YSH.

Five Mutable Types

YSH containers:

• List Dict - arbitrarily recursive

A special YSH type for "out params":

• Place - created by &myvar, and mutated by call place->setValue(42)

Containers for bash compatibility in OSH:

• BashArray BashAssoc - flat

Obj is for User-defined Types

• Obj - has a prototype chain

Objects allow polymorphism. See YSH Objects.

Modules and types are represented by Obj instances of a certain shape, not by primitive types.

1. Modules are Obj with attributes, and an __invoke__ method.
2. Types are Obj with a __str__ method, and are often compared for identity.

In general, Objects are mutable. Do not mutate modules or types!

Five Units of Code

Values of these types are immutable:

• BoundFunc (for methods)
• BuiltinFunc Func
• BuiltinProc Proc

Five Types for Reflection

Values of these types are immutable:

• CommandFrag Command
• Expr (no ExprFrag for now)

A handle to a stack frame:

• Frame - implicitly mutable, by setvar, etc.

Appendix

The JSON Data Model

These types can be serialized to and from JSON:

• Null Str Int Float List Dict

Why Isn't Everything an Object?

In YSH, the Obj type is used for polymorphism and reflection.

Polymorphism is when you hide different kinds of data behind the same interface.

But most shell scripts deal with concrete textual data, which may be JSON-like or TSV-like. The data is not hidden or encapsulated, and shouldn't be.

Implementation Details

These types used internally:

• value.Undef - used when looking up a variable
• value.Interrupted - for SIGINT
• value.Slice - for a[1:2]

Related

• Types and Methods in the Oils Reference