When you evaluate an expression at the compile-time, all the operands have to
be compile-time expressions (mostly literals, constants and expressions
consisted of them) in that context.
When you write
"123"
Run
Then `"123"` can be used as a compile-time expression.
When you write
const text = "123"
Run
Then `text` can be used as a compile-time expression.
However, when you write
var text = "123"
Run
`text` cannot be used as a compile-time expression, because it is considered a
runtime variable (`var`). The same applies to let-variables.
When you write
static:
var text = "123" & "4"
text
Run
This whole `static`-expression is a compile-time expression once resolved. But
within the context of this inner block, `text` is still not considered static.
Complex. I know. Just think of it as stack-like.
Also it seems that the lengths of arrays are always considered static, while
that of string/seq are not (and thus as static as the associated variable).
