pure recursive subroutine generate_nfa(tree, idx, nfa, entry_i, exit_i)
use :: forgex_enums_m, only: op_char, op_empty, op_closure, op_concat, op_repeat, op_union
use :: forgex_parameters_m, only: INFINITE, INVALID_INDEX
implicit none
type(tree_t), intent(in) :: tree
integer(int32), intent(in) :: idx
type(nfa_graph_t), intent(inout) :: nfa
integer(int32), intent(in) :: entry_i, exit_i
integer :: i
integer :: k
integer :: node1, node2, entry_local
if (idx == INVALID_INDEX) return
i = idx
entry_local = entry_i
select case(tree%nodes(i)%op)
case (op_char)
! Handle character operations by adding transition for each character.
call nfa%graph(entry_i)%add_transition(entry_i, exit_i, tree%nodes(i)%c)
case (op_empty)
! Handle empty opration by adding an epsilon transition
call nfa%graph(entry_i)%add_transition(entry_i, exit_i, [SEG_EPSILON])
case (op_closure)
! Handle closure (Kleene star) operations by creating new node and adding appropriate transition
call generate_nfa_closure(tree, idx, nfa, entry_i, exit_i)
case (op_union)
! Handle union operation by recursively generating NFA for left and right subtrees.
call generate_nfa(tree, tree%nodes(i)%left_i, nfa, entry_i, exit_i)
call generate_nfa(tree, tree%nodes(i)%right_i, nfa, entry_i, exit_i)
case (op_concat)
! Handle concatenation operations by recursively generating NFA for left and right subtrees.
call generate_nfa_concatenate(tree, idx, nfa, entry_i, exit_i)
case (op_repeat)
block
integer(int32) :: min_repeat, max_repeat, j
integer(int32) :: num_1st_repeat, num_2nd_repeat
min_repeat = tree%nodes(i)%min_repeat
max_repeat = tree%nodes(i)%max_repeat
num_1st_repeat = min_repeat-1
if (max_repeat == INFINITE) then
num_1st_repeat = num_1st_repeat +1
end if
do j = 1, num_1st_repeat
call nfa%new_nfa_node()
if (nfa%is_exceeded()) call nfa%reallocate()
node1 = nfa%top
call generate_nfa(tree, tree%nodes(i)%left_i, nfa, entry_local, node1)
entry_local = node1
end do
if (min_repeat == 0) then
num_2nd_repeat = max_repeat - 1
else
num_2nd_repeat = max_repeat - min_repeat
end if
do j = 1, num_2nd_repeat
call nfa%new_nfa_node()
if (nfa%is_exceeded()) call nfa%reallocate()
node2 = nfa%top
call generate_nfa(tree, tree%nodes(i)%left_i, nfa, entry_local, node2)
call nfa%graph(node2)%add_transition(node2, exit_i, [SEG_EPSILON])
entry_local = node2
end do
if (min_repeat == 0) then
call nfa%graph(entry_i)%add_transition(entry_i, exit_i, [SEG_EPSILON])
end if
if (max_repeat == INFINITE) then
call generate_nfa_closure(tree, idx, nfa, entry_local, exit_i)
else
call generate_nfa(tree, tree%nodes(i)%left_i, nfa, entry_local, exit_i)
end if
end block
case default ! for case (op_not_init)
! Handle unexpected cases.
error stop "This will not heppen in 'generate_nfa'."
! error stop tree%nodes(i)%op
end select
end subroutine generate_nfa