Haskell Lambda help - Splitting up terms from a lambda-term input

Question

I am trying to create a function in which given a lambda term will return all separate lambda terms

Here is my findT function:

findT :: T -> [T]
findT (V x) = []
findT (L x n) = [] ++ findT n
findT (A  n m) = [n] ++ findT m

When I run this function on two separate tests, it works with the first but not the second.

Answer 1

You can look if n is a Variable, and if so, do not include it, for example with:

findTerms :: Term -> [Term]
findTerms (Variable x) = []
findTerms (Lambda x n) = findTerms n
findTerms (Apply (Variable _) m) = findTerms m
findTerms (Apply n m) = n : findTerms m

Here if the first parameter of Apply is a Variable _, we will thus not consider it, otherwise we will yield n in the list.

You probably should also recurse on n and m, since that can contain terms as well. For a lambda you then can return the lambda itself:

findTerms :: Term -> [Term]
findTerms (Variable x) = []
findTerms l@(Lambda _ _) = [l]
findTerms (Apply n m) = findTerms n ++ findTerms m