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module semigroup_m
implicit none
private
public :: semigroup, extended_semigroup, derive_extended_semigroup
requirement semigroup(T, combine)
type, deferred :: T
elemental function combine(x, y) result(combined)
type(T), intent(in) :: x, y
type(T) :: combined
end function
end requirement
requirement extended_semigroup(T, combine, sconcat, stimes)
require :: semigroup(T, combine)
pure function sconcat(list) result(combined)
type(T), intent(in) :: list(:) !! Must contain at least one element
type(T) :: combined
end function
elemental function stimes(n, a) result(repeated)
integer, intent(in) :: n
type(T), intent(in) :: a
type(T) :: repeated
end function
end requirement
template derive_extended_semigroup(T, combine)
require :: semigroup(T, combine)
private
public :: sconcat, stimes
contains
pure function sconcat(list) result(combined)
type(T), intent(in) :: list(:)
type(T) :: combined
integer :: i
if (size(list) > 0) then
combined = list(1)
do i = 2, size(list)
combined = combine(combined, list(i))
end do
else
error stop "Attempted to sconcat empty list"
end if
end function
elemental function stimes(n, a) result(repeated)
integer, intent(in) :: n
type(T), intent(in) :: a
type(T) :: repeated
integer :: i
if (n < 1) error stop "n must be > 0"
repeated = a
do i = 2, n
repeated = combine(repeated, a)
end do
end function
end template
end module
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