## VSL - The `prelude.option` Structure

# Copyright 2011 Petter Urkedal
#
# This file is part of the Viz Standard Library <http://www.vizlang.org/>.
#
# The Viz Standard Library (VSL) is free software: you can redistribute it
# and/or modify it under the terms of the GNU Lesser General Public License as
# published by the Free Software Foundation, either version 3 of the License,
# or (at your option) any later version.
#
# The VSL is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
# more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with the VSL. If not, see <http://www.gnu.org/licenses/>.
open prereq
open effect
let is_empty
at none% be true
at some _ be false
let get
at none% fail "option.get none%"
at some x be x
let default x
at none% be x
at some y be y
let map f
at none% be none
at some x be some (f x)
let fold f
at none% be x ↦ x
at some x be f x
let for_all f
at none% be true
at some x be f x
let for_some f
at none% be false
at some x be f x
let iter f
at none% be return ()
at some x be f x
let filter f
at none% be none
at some x if f x be some x
else be none
let flatten
at some (some x) be some x
at _ be none