Curry: An Integrated Functional Logic Language

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if bk then ek else undefined
where decls
Transform where into let:
Each unconditional rule of the form
l = r where decls
is transformed into
l = let decls in r .
Each conditional rule of the form
l | c = r [ where decls ]
is transformed into
l = [ let decls in ] (c|r)
where the meaning of the guarded expression (c|r) is explained in Figure 3. Thus, we assume
in the subsequent transformations that all program rules are of the form “l = r” (where r might
be a let-expression).
Note that this transformation is not really necessary but provides for a unified treatment of
the elimination of local pattern and function declarations in let and where.
Eliminate local patterns and functions:
All local pattern and function declarations in a rule “l = r” are eliminated by iterating the
elimination of outermost local declarations as follows. For this purpose, we denote by r =
C[let decls in e]p an outermost let declaration in r, i.e., there is no prefix position p ′ < p
in r with r|p ′ = let . . .
We apply the following transformations as long as possible to eliminate all local pattern and
function declarations in a rule of the form “l = C[let decls in e]p”:
Eliminate patterns:
Select a local pattern declaration which contains only argument variables from the main
function’s left-hand side in the expression, i.e., the rule has the form
l = C[let decls1
p = e ′
in e]p
decls2
with free(e ′ ) ⊆ free(l) (it is a programming error if no pattern declaration has this
property, i.e., cyclic pattern definitions or pattern definitions depending on locally free
variables are not allowed). Then transform this rule into the rules
l = C[f ′ x1 . . . xk e ′ ]p
f ′ x1 . . . xk z = f ′′ x1 . . . xk (f1 z) . . . (fm z)
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