Curry: An Integrated Functional Logic Language

f ′′ x1 . . . xk y1 . . . ym = let decls1
f1 p = y1
...
fm p = ym
decls2
in e
where x1 . . . xk are all the variables occurring in l, y1 . . . ym are all the variables occurring
in p, z is a new variable symbol, and f ′ , f ′′ , f1, . . . , fm are new function symbols. Repeat
this step for f ′′ until all local pattern declarations are eliminated.
This translation can be optimized in some specific cases. If p is just a variable, the
function f ′ is not needed and the definition of l can be simplified into
l = C[f ′′ x1 . . . xk e ′ ]p
Similarly, if e ′ is a variable, the function f ′ is also not needed and the definition of l can
be replaced by
l = C[f ′′ x1 . . . xk (f1 e ′ ) . . . (fm e ′ )]p
Complete local function definitions:
If a locally declared function f refers in its definition to a variable v not contained in
its argument patterns, then add v as an additional first 23 argument to all occurrences
of f (i.e., left-hand sides and calls). Repeat this step until all locally defined functions
are completed. Note that this completion step must also be applied to free variables
introduced in the same let expression, i.e., the rule
f x = let y free
g z = c y z
in g 0
is completed to
f x = let y free
g y z = c y z
in g y 0
Globalize local function definitions:
If the definitions of all locally declared functions are completed, i.e., the definitions only
refer to variables in the argument patterns, delete the locally declared functions and
define them at the top-level (and rename them if there are already top-level functions
with the same name). For instance, the previous rule is transformed into the definitions
g y z = c y z
f x = let y free in g y 0
Note that the entire transformation process must be applied again to the new top-level
declarations since they may also contain local declarations.
23 The new arguments must come first because of possible partial applications of this function.
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