bossLib.namedCases

STRUCTURE

SYNOPSIS

Case split on type of leading universally quantified variable in the goal, using given names for introduced constructor arguments.

DESCRIPTION

An application of namedCases [s1, ..., sn] to a goal of the form !x:ty. P will perform a case split on the type ty, using the given names for the arguments of the introduced constructor terms. The type ty should be that of a dataype that has a so-called "nchotomy" theorem installed in the system database of declared datatypes, accessible via TypeBase.nchotomy_of.

For a datatype with n constructors, n strings are expected to be supplied. If no strings are supplied, the system will use a default naming scheme. If the ith constructor has no arguments, then si should be the empty string. If the ith constructor has k arguments, then si should consist of k space-separated names. In case a name does not need to be specified, an underscore _ or dash - can be supplied, in which case a default name will be conjured up.

In case ty is a product type ty1 # ... # tyi, namedCases [s] will iteratively case split on all product types in ty, thus replacing x:ty by a tuple with i variables, the names of which are taken from s.

FAILURE

Fails if there is not an nchotomy theorem installed for the topmost type constructor of ty. If slist is not the empty list, namedCases slist will fail if the length of slist is not equal to the number of constructors in the nchotomy theorem. Fails if the given names for arguments of an introduced constructor are not equinumerous with the arguments.

EXAMPLE

Consider the goal

     A ?- !x:num#num#bool. P x

Invoking namedCases ["a b c"] yields the goal

     A ?- P (a,b,c)

while namedCases ["a _ _"] yields the goal

     A ?- P (a,_gv0,_gv1)

EXAMPLE

Consider a datatype of arithmetic expressions declared as

   Datatype:
     arith
       = Var 'a
       | Const num
       | Add arith arith
       | Sub arith arith
       | Mult arith arith
   End

and the goal

     A ?- !x:'a arith. P x

Invoking namedCases ["v","c","a1 a2", "s1 s2", "m1 m2"] yields the following 5 goals

   P (Mult m1 m2)

   P (Sub s1 s2)

   P (Add a1 a2)

   P (Const c)

   P (Var v)

SEEALSO

namedCases_on, Cases_on, Cases, nchotomy_of