It's always "from one language to another", sometimes the destination is machine language. The output is generally not meant to be meant to be human-readable in any case. "Transpile" is an ugly and unnecessary word, please don't push it as "more correct".
"Transpilation" and "compilation" describe the exact same concept. From user's perspective, readable code is translated into runnable code. From theoretical perspective, code in a more complex language is translated into a less complex language while preserving semantics. From a compiler writer's perspective, it's a totem pole of compilers, with at least one middle-level language usually. Plenty of people use the term "compiles to JavaScript" to describe languages like TS or Elm. It's just some overly pedantic people insist on the term "transpile" when the target is also, in a completely unrelated way, used to write code directly by a significant number of contemporary programmers.
> "Transpilation" and "compilation" describe the exact same concept.
No I think transpile implies compiling from one level of abstraction to another similar level of abstraction, which is quite different in theory and practice to compiling to a much lower level of abstraction. It's a useful word to have in your communication toolbox.
I agree with your overall definition. In fact, the dictionary definition of compile does also suggest that you are transforming to a 'lower level' so, in strictness, there is a need for a word to fill the void that you suggest transpile provides.
But I do wonder about the actual usefulness of the distinction. If someone says that they compile Typescript to Javascript, I'm not sure that anyone is going to be confused about what is meant, even if violates the letter of the dictionary definition.
Ultimately, english is fluid and is always correct as long as those in communication are able to understand each other. For transpile to be a useful word in the toolbox, there must be a circumstance where compile cannot be used to convey the same idea. When might that be?
'This is a transpiler' gives me a massive amount of additional context compared to 'this is a compiler' - likely structure, implementation techniques, output. Not all transpilers will fit this usual structure, but if they do you can tell me by changing this one little word. Powerful communication tool, I think.
But neither 'this is a transpiler' or 'this is a compiler' provide any meaningful information without specifying the compatible inputs and outputs. Once the inputs and outputs are specified then it is already reasonably known if the operation is transpilation or compilation, making the distinction between transpiler and compiler redundant.
Fine, but by that logic, gcc with -O0 is a transpiler, and becomes a compiler again with -O2. Similarly, TS transpiles to JS, but, say, ClojureScript compiles to JS. And if a compiler is built with something like Nanopass, it's a sequence of transpilers that somehow become a compiler along the way.
Transpile is a superset or compile just like typescript is a superset of JavaScript. Transpile implies translating but not into a less complex language but rather onto a similar runtime. So typescript is dynamic just like JavaScript, and they share much of their semantics. So transpile means compile but onto a similar runtime with similar runtime semantic behavior.
In that case surely you'd agree that there are hardly any compilers in wide use these days - more often than not the first step of a modern compiler is translation into a similar but less expressive intermediate language.
Or does it only count as "transpilation" if the intermediate representation is an already existing language, thus making the distincion purely based on the history of a language, not the implementation?
