Curry: An Integrated Functional Logic Language

In the last translation rule, concatMap is defined in the prelude (see page 51) and complP at(p)
denotes the set of patterns that are incompatible with p. This set is defined by
complP at(x) = {}
for all variables x and
complP at(C p1 . . . pn) = {C1 x11 . . . x1n1 , . . . , Ck xk1 . . . xknk }
∪ {C p1 . . . pi−1 p ′ yi+1 . . . yn | 1 ≤ i ≤ n, p ′ ∈ complP at(pi)}
where C, C1, . . . , Ck are all the constructors of the result type of C and all xij, yi are fresh variables.
For instance, complP at([True]) = {[], False:zs, True:y:ys} and complP at((x,y)) = {}.
Note that this translation does not work for patterns containing number constants since in this
case the complement set of patterns is infinite. Therefore, we modify this scheme as follows. If the
pattern p in a list comprehension [e | p en
Note that case expressions use the layout rule (see Section C.2). Thus, the patterns p1, . . . , pn
must be vertically aligned. The informal operational meaning of the case expression is as follows.
Evaluate e so that it matches a pattern pi. If this is possible, replace the entire case expression
by the corresponding alternative ei (after replacing the pattern variables occurring in pi by their
actual expressions). If none of the patterns p1, . . . , pn matches, the computation fails. The pattern
matching is tried sequentially, from top to bottom, and rigid, without binding of free variables
occurring in e. Thus, case expressions correspond to rigid functions. Actually, each case expression
can be translated into an auxiliary function so that case expressions do not increase the power of the
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