Odd bug here... The file lambda.hs contains: main = print ((\x -> x * x) (2.0 :: Float)) This is the output for compiling for hat, and not for hat: Looking at the traces, the recorded trace computes the correct answer (in fact, 16 can't be found anywhere in the trace), but the incorrect answer is output. alduruch:~/Documents/Work/Hat test cases/Lambda tatd2$ rm lambda.o alduruch:~/Documents/Work/Hat test cases/Lambda tatd2$ rm Hat/lambda.o alduruch:~/Documents/Work/Hat test cases/Lambda tatd2$ rm lambda alduruch:~/Documents/Work/Hat test cases/Lambda tatd2$ hmake lambda ghc -c -o lambda.o lambda.hs ghc -o lambda lambda.o alduruch:~/Documents/Work/Hat test cases/Lambda tatd2$ ./lambda 4.0 alduruch:~/Documents/Work/Hat test cases/Lambda tatd2$ rm lambda alduruch:~/Documents/Work/Hat test cases/Lambda tatd2$ hmake -hat lambda hat-trans lambda.hs Wrote Hat/lambda.hs ghc -c -package hat -o Hat/lambda.o Hat/lambda.hs ghc -package hat -o lambda Hat/lambda.o alduruch:~/Documents/Work/Hat test cases/Lambda tatd2$ ./lambda 16.0