FAQ

Common questions about Tao, answered from the actual implementation.

Does Tao have classes and inheritance?

No. A data type declares fields, but there is no inheritance. To extend a type, write a receiver method:

fun (p Point) area() { p.x * p.y }

Two types may define a method of the same name; each is dispatched by the receiver’s type.

Why are 0, "", and [] true?

Tao follows its own truthiness law: only None and False are false. Every other value — including 0, "", and [] — is true. This matches Ruby.

How do I concatenate strings?

"a" + "b" is an error. Use interpolation instead:

let name = "world"
"hello \(name)"

Interpolation accepts a simple identifier, not an arbitrary expression.

How do I handle errors?

Functions that can fail return a [val, err] list. Unpack it by hand with let val, err = expr, or let try expr return the error from the current function. There are no exceptions and no raise.

Is there a map or dictionary type?

No. Tao’s only collection is the List, and its only built-in values are Int, Float, Bool, None, String, and List. A data type is the way to group values.

Is there concurrency?

No. Programs run on a single thread, and there are no fibers, threads, or actors.

Why can’t I call a method like a function?

A receiver method is dispatched on its instance, not bound as a global name. add(4) alone fails with an undefined variable; p.add(4) works.

Can leave be used outside a loop? Can try be used outside a function?

No to both. leave is only valid inside a loop, and try only inside a function. Both are checked at parse time.

Can I redefine a name?

No. Every name — variable, function, or type — may be defined exactly once in its scope. Redefining reports already defined variable: x.

Can a data field default to an expression?

No. Field defaults are evaluated at construction and must be literals (Int, Float, String, Bool, None, or a list of those). An identifier or call is rejected.

How is Tao related to Ruby?

Tao is implemented in Ruby and shares some ideas — truthiness, string interpolation — but it is a separate language with its own syntax and rules.

Where do package and import fit in?

Both are parsed today and reserved for the standard modules, which are not implemented yet. Only the io.println built-in is available directly.