An Embedded Type Debugger
This paper presents how to build a type debugger without implementing
any dedicated type inferencer.
Previous type debuggers required their own type inferencers apart from
the compiler's type inferencer.
The advantage of our approach is threefold.
First, by not implementing a type inferencer, it is guaranteed
that the debugger's type inference never disagrees with the compiler's
Secondly, we can avoid the pointless reproduction of a type inferencer
that should work precisely as the compiler's type inferencer.
Thirdly, our approach is robust to updates of the underlying language.
The key observation of our approach is that the interactive type
debugging, as proposed by Chitil, does not require a type inference
tree but only a tree with a certain simple property.
We identify the property and present how to construct a tree that
satisfies this property using the compiler's type inferencer.
The property guides us how to build a type debugger for various
In this paper, we describe our idea and first apply it to the
simply-typed lambda calculus.
After that, we extend it with let-polymorphism and objects to see how
our technique scales.