No, large parts of Gradle are actually implemented in Groovy. You're referring to the DSL, which can be used purely declaratively, but it's not limited to such use (you can use all Groovy language featured in Gradle scripts).
> large parts of Gradle are actually implemented in Groovy
I thought it was just the plugin and DSL handling code. That would explain why Gradle's so slow, then.
> the DSL, which can be used purely declaratively, but it's not limited to such use
Virtually no-one uses Groovy procedurally, only declaratively, in Gradle build scripts, so although that's true in theory, in practise only the non-Turing Complete portions of Groovy are used. Calling it a programming language there is like calling HTML one because you can embed Javascript in HTML.