There are two kinds of holes in the surface syntax: ? and _.
? stands for parts of the program that have not been completed yet, and where we expect the compiler to help us with finding the right term to fill in.
_ are parts of the program where we expect the compiler to find a unique solution by unification, and where we can't be bothered to write out the term.
The compiler should throw an error if it can't find a unique solution for _.
There are two kinds of holes in the surface syntax:
?and_.?stands for parts of the program that have not been completed yet, and where we expect the compiler to help us with finding the right term to fill in._are parts of the program where we expect the compiler to find a unique solution by unification, and where we can't be bothered to write out the term. The compiler should throw an error if it can't find a unique solution for_.