On Friday 01 April 2011 10:49:53, Yves Parès wrote:
Then if you turn :
fs True = True fs x = True
to:
fs x = case x of True -> True x' -> True
Is it still strict, or does 'fs' wrap the case test and defer evaluation?
It's still strict, to produce a result, fs has to pattern-match its argument, pattern matching is strict. The report says: "Patterns appear in lambda abstractions, function definitions, pattern bindings, list comprehensions, do expressions, and case expressions. However, the first five of these ultimately translate into case expressions, so defining the semantics of pattern matching for case expressions is sufficient. " So I think the report mandates that both forms are equivalent. You get exactly the same code as for gs :: Bool -> Bool gs x = x `seq` True or hs :: Bool -> Bool hs x = if x then True else True with GHC (with or without optimisations) btw.