A tagged union can be represented as a closed interface.
In the provided example, there is a closed interface isf.T, which holds either an int, a string or a float. Well, an isf.Int, an isf.String, or an isf.Float, technically.
To match on the union, we need a matching construct.
A pattern matching construct can be represented as dispatching function, which takes our union and a handling closure for each possible case in the union.
In the provided example, the function is named isf.Match. It receives an isf.T and a bunch of handlers.
The file main.go is provided with usage examples.
No measurements have been conducted.
I doubt this will perform well, unless inlined by the compiler.
Since performance requirements vary depending on the task at hand, this may be acceptable.
The expat license.