Semantic Analysis - Crafting a Compiler - page 372

function subsumes L ater C atches ( exceptionType , Catching cn ) returns Boolean

if null

then return false
else

cn =

if ( exceptionType , cn . catchIdDecl . type )

then return ( true )
else
return subsumes

assignable

( exceptionType , cn . more )

L ater C atches

end

procedure (SetOfType throwsSet ,Catching cn )

f ilteredThrowsSet ← filter

process C atch

T hrows ( throwsSet , cn . catchIdDecl . type )

if f ilteredThrowsSet = throwsSet
then call error (” No throws reach this catch ”)

else

if cn . more null

then call process C atch ( f ilteredThrowsSet , cn . more )

end

function filter T hrows ( SetOfType throwsSet , exceptionType ) returns SetO f Type

ans ←∅
foreach t ∈ throwsSet do
if not assignable ( exceptionType , t )

then ans ← ans ∪ t
return ( ans )

end

function filter C atches (SetOfType throwsSet , Catching cn ) returns SetO f Type

if null

then return filter

cn . more =

( throwsSet , cn . catchIdDecl . type ) T hrows

else
return filter , cn . more ) C atches ( filter T hrows ( throwsSet , cn . catchIdDecl . type )

end

procedure update C atch L ist (Catching cn )

call extend C atch L ist ( cn . catchIdDecl . type )

if null

then call update

cn . more

C atch L ist ( cn . more )

end

Figure 9.27: Utility Semantic Methods for Try and Throw Statements