lib: rename `standard` as `core`

[nit.git] / lib / core / text / flat.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# This file is free software, which comes along with NIT.  This software 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.  You can modify it is you want,  provided this header
# is kept unaltered, and a notification of the changes is added.
# You  are  allowed  to  redistribute it and sell it, alone or is a part of
# another product.

# All the array-based text representations
module flat

intrude import abstract_text
intrude import native

`{
#include <stdio.h>
#include <string.h>
`}

private class FlatSubstringsIter
        super Iterator[FlatText]

        var tgt: nullable FlatText

        redef fun item do
                assert is_ok
                return tgt.as(not null)
        end

        redef fun is_ok do return tgt != null

        redef fun next do tgt = null
end

redef class FlatText

        private fun first_byte: Int do return 0

        private fun last_byte: Int do return bytelen - 1

        # Cache of the latest position (char) explored in the string
        var position: Int = 0

        # Cached position (bytes) in the NativeString underlying the String
        var bytepos: Int = first_byte is lateinit

        # Index of the character `index` in `items`
        private fun char_to_byte_index(index: Int): Int do
                var ln = length
                assert index >= 0
                assert index < ln

                # Find best insertion point
                var delta_begin = index
                var delta_end = (ln - 1) - index
                var delta_cache = (position - index).abs
                var min = delta_begin
                var its = items

                if delta_cache < min then min = delta_cache
                if delta_end < min then min = delta_end

                var ns_i: Int
                var my_i: Int

                if min == delta_begin then
                        ns_i = first_byte
                        my_i = 0
                else if min == delta_cache then
                        ns_i = bytepos
                        my_i = position
                else
                        ns_i = its.find_beginning_of_char_at(last_byte)
                        my_i = length - 1
                end

                ns_i = its.char_to_byte_index_cached(index, my_i, ns_i)

                position = index
                bytepos = ns_i

                return ns_i
        end

        redef fun [](index) do return items.char_at(char_to_byte_index(index))
end

# Immutable strings of characters.
class FlatString
        super FlatText
        super String

        # Index at which `self` begins in `items`, inclusively
        redef var first_byte is noinit

        # Index at which `self` ends in `items`, inclusively
        redef var last_byte is noinit

        redef var chars = new FlatStringCharView(self) is lazy

        redef var bytes = new FlatStringByteView(self) is lazy

        redef var length is lazy do
                if bytelen == 0 then return 0
                var st = first_byte
                var its = items
                var ln = 0
                var lst = last_byte
                while st <= lst do
                        st += its.length_of_char_at(st)
                        ln += 1
                end
                return ln
        end

        redef fun reversed
        do
                var b = new FlatBuffer.with_capacity(bytelen + 1)
                for i in [length - 1 .. 0].step(-1) do
                        b.add self[i]
                end
                var s = b.to_s.as(FlatString)
                s.length = self.length
                return s
        end

        redef fun fast_cstring do return items.fast_cstring(first_byte)

        redef fun substring(from, count)
        do
                assert count >= 0

                if from < 0 then
                        count += from
                        if count < 0 then count = 0
                        from = 0
                end

                if (count + from) > length then count = length - from
                if count <= 0 then return ""
                var end_index = from + count - 1

                var bytefrom = char_to_byte_index(from)
                var byteto = char_to_byte_index(end_index)
                byteto += items.length_of_char_at(byteto) - 1

                var s = new FlatString.full(items, byteto - bytefrom + 1, bytefrom, byteto, count)
                return s
        end

        redef fun empty do return "".as(FlatString)

        redef fun to_upper
        do
                var outstr = new FlatBuffer.with_capacity(self.bytelen + 1)

                var mylen = length
                var pos = 0

                while pos < mylen do
                        outstr.add(chars[pos].to_upper)
                        pos += 1
                end

                return outstr.to_s
        end

        redef fun to_lower
        do
                var outstr = new FlatBuffer.with_capacity(self.bytelen + 1)

                var mylen = length
                var pos = 0

                while pos < mylen do
                        outstr.add(chars[pos].to_lower)
                        pos += 1
                end

                return outstr.to_s
        end

        redef fun output
        do
                for i in chars do i.output
        end

        ##################################################
        #              String Specific Methods           #
        ##################################################

        # Low-level creation of a new string with minimal data.
        #
        # `items` will be used as is, without copy, to retrieve the characters of the string.
        # Aliasing issues is the responsibility of the caller.
        private init with_infos(items: NativeString, bytelen, from, to: Int)
        do
                self.items = items
                self.bytelen = bytelen
                first_byte = from
                last_byte = to
        end

        # Low-level creation of a new string with all the data.
        #
        # `items` will be used as is, without copy, to retrieve the characters of the string.
        # Aliasing issues is the responsibility of the caller.
        private init full(items: NativeString, bytelen, from, to, length: Int)
        do
                self.items = items
                self.length = length
                self.bytelen = bytelen
                first_byte = from
                last_byte = to
        end

        redef fun to_cstring do
                if real_items != null then return real_items.as(not null)
                var new_items = new NativeString(bytelen + 1)
                self.items.copy_to(new_items, bytelen, first_byte, 0)
                new_items[bytelen] = 0u8
                real_items = new_items
                return new_items
        end

        redef fun ==(other)
        do
                if not other isa FlatString then return super

                if self.object_id == other.object_id then return true

                var my_length = bytelen

                if other.bytelen != my_length then return false

                var my_index = first_byte
                var its_index = other.first_byte

                var last_iteration = my_index + my_length

                var itsitems = other.items
                var myitems = self.items

                while my_index < last_iteration do
                        if myitems[my_index] != itsitems[its_index] then return false
                        my_index += 1
                        its_index += 1
                end

                return true
        end

        redef fun <(other)
        do
                if not other isa FlatString then return super

                if self.object_id == other.object_id then return false

                var my_length = self.bytelen
                var its_length = other.bytelen

                var max = if my_length < its_length then my_length else its_length

                var myits = self.bytes
                var itsits = other.bytes

                for i in [0 .. max[ do
                        var my_curr_char = myits[i]
                        var its_curr_char = itsits[i]

                        if my_curr_char != its_curr_char then
                                if my_curr_char < its_curr_char then return true
                                return false
                        end
                end

                return my_length < its_length
        end

        redef fun +(o) do
                var s = o.to_s
                var slen = s.bytelen
                var mlen = bytelen
                var nlen = mlen + slen
                var mits = items
                var mifrom = first_byte
                if s isa FlatText then
                        var sits = s.items
                        var sifrom = s.first_byte
                        var ns = new NativeString(nlen + 1)
                        mits.copy_to(ns, mlen, mifrom, 0)
                        sits.copy_to(ns, slen, sifrom, mlen)
                        return new FlatString.full(ns, nlen, 0, nlen - 1, length + o.length)
                else
                        abort
                end
        end

        redef fun *(i) do
                var mybtlen = bytelen
                var new_bytelen = mybtlen * i
                var mylen = length
                var newlen = mylen * i
                var ns = new NativeString(new_bytelen + 1)
                ns[new_bytelen] = 0u8
                var offset = 0
                while i > 0 do
                        items.copy_to(ns, bytelen, first_byte, offset)
                        offset += mybtlen
                        i -= 1
                end
                return new FlatString.full(ns, new_bytelen, 0, new_bytelen - 1, newlen)
        end


        redef fun hash
        do
                if hash_cache == null then
                        # djb2 hash algorithm
                        var h = 5381
                        var i = first_byte

                        var myitems = items

                        while i <= last_byte do
                                h = (h << 5) + h + myitems[i].to_i
                                i += 1
                        end

                        hash_cache = h
                end

                return hash_cache.as(not null)
        end

        redef fun substrings do return new FlatSubstringsIter(self)
end

private class FlatStringCharReverseIterator
        super IndexedIterator[Char]

        var target: FlatString

        var curr_pos: Int

        init with_pos(tgt: FlatString, pos: Int)
        do
                init(tgt, pos)
        end

        redef fun is_ok do return curr_pos >= 0

        redef fun item do return target[curr_pos]

        redef fun next do curr_pos -= 1

        redef fun index do return curr_pos

end

private class FlatStringCharIterator
        super IndexedIterator[Char]

        var target: FlatString

        var max: Int

        var curr_pos: Int

        init with_pos(tgt: FlatString, pos: Int)
        do
                init(tgt, tgt.length - 1, pos)
        end

        redef fun is_ok do return curr_pos <= max

        redef fun item do return target[curr_pos]

        redef fun next do curr_pos += 1

        redef fun index do return curr_pos

end

private class FlatStringCharView
        super StringCharView

        redef type SELFTYPE: FlatString

        redef fun [](index) do return target[index]

        redef fun iterator_from(start) do return new FlatStringCharIterator.with_pos(target, start)

        redef fun reverse_iterator_from(start) do return new FlatStringCharReverseIterator.with_pos(target, start)

end

private class FlatStringByteReverseIterator
        super IndexedIterator[Byte]

        var target: FlatString

        var target_items: NativeString

        var curr_pos: Int

        init with_pos(tgt: FlatString, pos: Int)
        do
                init(tgt, tgt.items, pos + tgt.first_byte)
        end

        redef fun is_ok do return curr_pos >= target.first_byte

        redef fun item do return target_items[curr_pos]

        redef fun next do curr_pos -= 1

        redef fun index do return curr_pos - target.first_byte

end

private class FlatStringByteIterator
        super IndexedIterator[Byte]

        var target: FlatString

        var target_items: NativeString

        var curr_pos: Int

        init with_pos(tgt: FlatString, pos: Int)
        do
                init(tgt, tgt.items, pos + tgt.first_byte)
        end

        redef fun is_ok do return curr_pos <= target.last_byte

        redef fun item do return target_items[curr_pos]

        redef fun next do curr_pos += 1

        redef fun index do return curr_pos - target.first_byte

end

private class FlatStringByteView
        super StringByteView

        redef type SELFTYPE: FlatString

        redef fun [](index)
        do
                # Check that the index (+ first_byte) is not larger than last_byte
                # In other terms, if the index is valid
                assert index >= 0
                var target = self.target
                assert (index + target.first_byte) <= target.last_byte
                return target.items[index + target.first_byte]
        end

        redef fun iterator_from(start) do return new FlatStringByteIterator.with_pos(target, start)

        redef fun reverse_iterator_from(start) do return new FlatStringByteReverseIterator.with_pos(target, start)

end

redef class Buffer
        redef new do return new FlatBuffer

        redef new with_cap(i) do return new FlatBuffer.with_capacity(i)
end

# Mutable strings of characters.
class FlatBuffer
        super FlatText
        super Buffer

        redef var chars: Sequence[Char] = new FlatBufferCharView(self) is lazy

        redef var bytes = new FlatBufferByteView(self) is lazy

        redef var bytelen = 0

        redef var length = 0

        private var char_cache: Int = -1

        private var byte_cache: Int = -1

        private var capacity = 0

        redef fun fast_cstring do return items.fast_cstring(0)

        redef fun substrings do return new FlatSubstringsIter(self)

        # Re-copies the `NativeString` into a new one and sets it as the new `Buffer`
        #
        # This happens when an operation modifies the current `Buffer` and
        # the Copy-On-Write flag `written` is set at true.
        private fun reset do
                var nns = new NativeString(capacity)
                items.copy_to(nns, bytelen, 0, 0)
                items = nns
                written = false
        end

        # Shifts the content of the buffer by `len` bytes to the right, starting at byte `from`
        #
        # Internal only, does not modify bytelen or length, this is the caller's responsability
        private fun rshift_bytes(from: Int, len: Int) do
                var oit = items
                var nit = items
                if bytelen + len > capacity then
                        capacity = capacity * 2 + 2
                        nit = new NativeString(capacity)
                        oit.copy_to(nit, 0, 0, from)
                end
                oit.copy_to(nit, bytelen - from, from, from + len)
        end

        # Shifts the content of the buffer by `len` bytes to the left, starting at `from`
        #
        # Internal only, does not modify bytelen or length, this is the caller's responsability
        private fun lshift_bytes(from: Int, len: Int) do
                items.copy_to(items, bytelen - from, from, from - len)
        end

        redef fun []=(index, item)
        do
                assert index >= 0 and index <= length
                if written then reset
                is_dirty = true
                if index == length then
                        add item
                        return
                end
                var ip = items.char_to_byte_index(index)
                var c = items.char_at(ip)
                var clen = c.u8char_len
                var itemlen = item.u8char_len
                var size_diff = itemlen - clen
                if size_diff > 0 then
                        rshift_bytes(ip + clen, size_diff)
                else if size_diff < 0 then
                        lshift_bytes(ip + clen, -size_diff)
                end
                bytelen += size_diff
                bytepos += size_diff
                items.set_char_at(ip, item)
        end

        redef fun add(c)
        do
                if written then reset
                is_dirty = true
                var clen = c.u8char_len
                enlarge(bytelen + clen)
                items.set_char_at(bytelen, c)
                bytelen += clen
                length += 1
        end

        redef fun clear do
                is_dirty = true
                if written then reset
                bytelen = 0
                length = 0
        end

        redef fun empty do return new Buffer

        redef fun enlarge(cap)
        do
                var c = capacity
                if cap <= c then return
                while c <= cap do c = c * 2 + 2
                # The COW flag can be set at false here, since
                # it does a copy of the current `Buffer`
                written = false
                var a = new NativeString(c+1)
                if bytelen > 0 then items.copy_to(a, bytelen, 0, 0)
                items = a
                capacity = c
        end

        redef fun to_s
        do
                written = true
                if bytelen == 0 then items = new NativeString(1)
                return new FlatString.with_infos(items, bytelen, 0, bytelen - 1)
        end

        redef fun to_cstring
        do
                if is_dirty then
                        var new_native = new NativeString(bytelen + 1)
                        new_native[bytelen] = 0u8
                        if length > 0 then items.copy_to(new_native, bytelen, 0, 0)
                        real_items = new_native
                        is_dirty = false
                end
                return real_items.as(not null)
        end

        # Create a new empty string.
        init do end

        # Low-level creation a new buffer with given data.
        #
        # `items` will be used as is, without copy, to store the characters of the buffer.
        # Aliasing issues is the responsibility of the caller.
        #
        # If `items` is shared, `written` should be set to true after the creation
        # so that a modification will do a copy-on-write.
        private init with_infos(items: NativeString, capacity, bytelen, length: Int)
        do
                self.items = items
                self.capacity = capacity
                self.bytelen = bytelen
                self.length = length
        end

        # Create a new string copied from `s`.
        init from(s: Text)
        do
                items = new NativeString(s.bytelen)
                if s isa FlatText then
                        items = s.items
                else
                        for i in substrings do i.as(FlatString).items.copy_to(items, i.bytelen, 0, 0)
                end
                bytelen = s.bytelen
                length = s.length
                capacity = s.bytelen
                written = true
        end

        # Create a new empty string with a given capacity.
        init with_capacity(cap: Int)
        do
                assert cap >= 0
                items = new NativeString(cap + 1)
                capacity = cap
                bytelen = 0
        end

        redef fun append(s)
        do
                if s.is_empty then return
                is_dirty = true
                var sl = s.bytelen
                enlarge(bytelen + sl)
                if s isa FlatText then
                        s.items.copy_to(items, sl, s.first_byte, bytelen)
                else
                        for i in s.substrings do append i
                        return
                end
                bytelen += sl
                length += s.length
        end

        # Copies the content of self in `dest`
        fun copy(start: Int, len: Int, dest: Buffer, new_start: Int)
        do
                var self_chars = self.chars
                var dest_chars = dest.chars
                for i in [0..len-1] do
                        dest_chars[new_start+i] = self_chars[start+i]
                end
        end

        redef fun substring(from, count)
        do
                assert count >= 0
                if from < 0 then from = 0
                if (from + count) > length then count = length - from
                if count != 0 then
                        var bytefrom = items.char_to_byte_index(from)
                        var byteto = items.char_to_byte_index(count + from - 1)
                        byteto += items.char_at(byteto).u8char_len - 1
                        var byte_length = byteto - bytefrom + 1
                        var r_items = new NativeString(byte_length)
                        items.copy_to(r_items, byte_length, bytefrom, 0)
                        return new FlatBuffer.with_infos(r_items, byte_length, byte_length, count)
                else
                        return new Buffer
                end
        end

        redef fun reverse
        do
                written = false
                var ns = new FlatBuffer.with_capacity(capacity)
                for i in chars.reverse_iterator do ns.add i
                items = ns.items
        end

        redef fun times(repeats)
        do
                var x = new FlatString.with_infos(items, bytelen, 0, bytelen - 1)
                for i in [1 .. repeats[ do
                        append(x)
                end
        end

        redef fun upper
        do
                if written then reset
                for i in [0 .. length[ do self[i] = self[i].to_upper
        end

        redef fun lower
        do
                if written then reset
                for i in [0 .. length[ do self[i] = self[i].to_lower
        end
end

private class FlatBufferByteReverseIterator
        super IndexedIterator[Byte]

        var target: FlatBuffer

        var target_items: NativeString

        var curr_pos: Int

        init with_pos(tgt: FlatBuffer, pos: Int)
        do
                init(tgt, tgt.items, pos)
        end

        redef fun index do return curr_pos

        redef fun is_ok do return curr_pos >= 0

        redef fun item do return target_items[curr_pos]

        redef fun next do curr_pos -= 1

end

private class FlatBufferByteView
        super BufferByteView

        redef type SELFTYPE: FlatBuffer

        redef fun [](index) do return target.items[index]

        redef fun iterator_from(pos) do return new FlatBufferByteIterator.with_pos(target, pos)

        redef fun reverse_iterator_from(pos) do return new FlatBufferByteReverseIterator.with_pos(target, pos)

end

private class FlatBufferByteIterator
        super IndexedIterator[Byte]

        var target: FlatBuffer

        var target_items: NativeString

        var curr_pos: Int

        init with_pos(tgt: FlatBuffer, pos: Int)
        do
                init(tgt, tgt.items, pos)
        end

        redef fun index do return curr_pos

        redef fun is_ok do return curr_pos < target.bytelen

        redef fun item do return target_items[curr_pos]

        redef fun next do curr_pos += 1

end

private class FlatBufferCharReverseIterator
        super IndexedIterator[Char]

        var target: FlatBuffer

        var curr_pos: Int

        init with_pos(tgt: FlatBuffer, pos: Int)
        do
                init(tgt, pos)
        end

        redef fun index do return curr_pos

        redef fun is_ok do return curr_pos >= 0

        redef fun item do return target[curr_pos]

        redef fun next do curr_pos -= 1

end

private class FlatBufferCharView
        super BufferCharView

        redef type SELFTYPE: FlatBuffer

        redef fun [](index) do return target[index]

        redef fun []=(index, item)
        do
                assert index >= 0 and index <= length
                if index == length then
                        add(item)
                        return
                end
                target[index] = item
        end

        redef fun push(c)
        do
                target.add(c)
        end

        redef fun add(c)
        do
                target.add(c)
        end

        fun enlarge(cap: Int)
        do
                target.enlarge(cap)
        end

        redef fun append(s)
        do
                var s_length = s.length
                if target.capacity < s.length then enlarge(s_length + target.length)
                for i in s do target.add i
        end

        redef fun iterator_from(pos) do return new FlatBufferCharIterator.with_pos(target, pos)

        redef fun reverse_iterator_from(pos) do return new FlatBufferCharReverseIterator.with_pos(target, pos)

end

private class FlatBufferCharIterator
        super IndexedIterator[Char]

        var target: FlatBuffer

        var max: Int

        var curr_pos: Int

        init with_pos(tgt: FlatBuffer, pos: Int)
        do
                init(tgt, tgt.length - 1, pos)
        end

        redef fun index do return curr_pos

        redef fun is_ok do return curr_pos <= max

        redef fun item do return target[curr_pos]

        redef fun next do curr_pos += 1

end

redef class NativeString
        redef fun to_s
        do
                return to_s_with_length(cstring_length)
        end

        # Returns `self` as a String of `length`.
        redef fun to_s_with_length(length): FlatString
        do
                assert length >= 0
                var str = new FlatString.with_infos(self, length, 0, length - 1)
                return str
        end

        # Returns `self` as a new String.
        redef fun to_s_with_copy: FlatString
        do
                var length = cstring_length
                var new_self = new NativeString(length + 1)
                copy_to(new_self, length, 0, 0)
                var str = new FlatString.with_infos(new_self, length, 0, length - 1)
                new_self[length] = 0u8
                str.real_items = new_self
                return str
        end

        # Sets the next bytes at position `pos` to the value of `c`, encoded in UTF-8
        #
        # Very unsafe, make sure to have room for this char prior to calling this function.
        private fun set_char_at(pos: Int, c: Char) do
                var ln = c.u8char_len
                native_set_char(pos, c, ln)
        end

        private fun native_set_char(pos: Int, c: Char, ln: Int) `{
                char* dst = self + pos;
                switch(ln){
                        case 1:
                                dst[0] = c;
                                break;
                        case 2:
                                dst[0] = 0xC0 | ((c & 0x7C0) >> 6);
                                dst[1] = 0x80 | (c & 0x3F);
                                break;
                        case 3:
                                dst[0] = 0xE0 | ((c & 0xF000) >> 12);
                                dst[1] = 0x80 | ((c & 0xFC0) >> 6);
                                dst[2] = 0x80 | (c & 0x3F);
                                break;
                        case 4:
                                dst[0] = 0xF0 | ((c & 0x1C0000) >> 18);
                                dst[1] = 0x80 | ((c & 0x3F000) >> 12);
                                dst[2] = 0x80 | ((c & 0xFC0) >> 6);
                                dst[3] = 0x80 | (c & 0x3F);
                                break;
                }
        `}
end

redef class Int
        redef fun to_base(base, signed)
        do
                var l = digit_count(base)
                var s = new FlatBuffer.from(" " * l)
                fill_buffer(s, base, signed)
                return s.to_s
        end

        # return displayable int in base 10 and signed
        #
        #     assert 1.to_s            == "1"
        #     assert (-123).to_s       == "-123"
        redef fun to_s do
                # Fast case for common numbers
                if self == 0 then return "0"
                if self == 1 then return "1"

                var nslen = int_to_s_len
                var ns = new NativeString(nslen + 1)
                ns[nslen] = 0u8
                native_int_to_s(ns, nslen + 1)
                return new FlatString.full(ns, nslen, 0, nslen - 1, nslen)
        end
end

redef class Array[E]

        # Fast implementation
        redef fun plain_to_s
        do
                var l = length
                if l == 0 then return ""
                if l == 1 then if self[0] == null then return "" else return self[0].to_s
                var its = _items
                var na = new NativeArray[String](l)
                var i = 0
                var sl = 0
                var mypos = 0
                while i < l do
                        var itsi = its[i]
                        if itsi == null then
                                i += 1
                                continue
                        end
                        var tmp = itsi.to_s
                        sl += tmp.bytelen
                        na[mypos] = tmp
                        i += 1
                        mypos += 1
                end
                var ns = new NativeString(sl + 1)
                ns[sl] = 0u8
                i = 0
                var off = 0
                while i < mypos do
                        var tmp = na[i]
                        if tmp isa FlatString then
                                var tpl = tmp.bytelen
                                tmp.items.copy_to(ns, tpl, tmp.first_byte, off)
                                off += tpl
                        else
                                for j in tmp.substrings do
                                        var s = j.as(FlatString)
                                        var slen = s.bytelen
                                        s.items.copy_to(ns, slen, s.first_byte, off)
                                        off += slen
                                end
                        end
                        i += 1
                end
                return ns.to_s_with_length(sl)
        end
end

redef class NativeArray[E]
        redef fun native_to_s do
                assert self isa NativeArray[String]
                var l = length
                var na = self
                var i = 0
                var sl = 0
                var mypos = 0
                while i < l do
                        sl += na[i].bytelen
                        i += 1
                        mypos += 1
                end
                var ns = new NativeString(sl + 1)
                ns[sl] = 0u8
                i = 0
                var off = 0
                while i < mypos do
                        var tmp = na[i]
                        if tmp isa FlatString then
                                var tpl = tmp.bytelen
                                tmp.items.copy_to(ns, tpl, tmp.first_byte, off)
                                off += tpl
                        else
                                for j in tmp.substrings do
                                        var s = j.as(FlatString)
                                        var slen = s.bytelen
                                        s.items.copy_to(ns, slen, s.first_byte, off)
                                        off += slen
                                end
                        end
                        i += 1
                end
                return ns.to_s_with_length(sl)
        end
end

redef class Map[K,V]
        redef fun join(sep, couple_sep)
        do
                if is_empty then return ""

                var s = new Buffer # Result

                # Concat first item
                var i = iterator
                var k = i.key
                var e = i.item
                s.append("{k or else "<null>"}{couple_sep}{e or else "<null>"}")

                # Concat other items
                i.next
                while i.is_ok do
                        s.append(sep)
                        k = i.key
                        e = i.item
                        s.append("{k or else "<null>"}{couple_sep}{e or else "<null>"}")
                        i.next
                end
                return s.to_s
        end
end