[nit.git] / lib / standard / string.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# Copyright 2004-2008 Jean Privat <jean@pryen.org>
# Copyright 2006-2008 Floréal Morandat <morandat@lirmm.fr>
#
# 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.

# Basic manipulations of strings of characters
package string

intrude import collection # FIXME should be collection::array
import hash

`{
#include <stdio.h>
`}

###############################################################################
# String                                                                      #
###############################################################################

# Common subclass for String and Buffer
abstract class AbstractString
        super AbstractArrayRead[Char]

        readable private var _items: NativeString

        # Access a character at `index` in the string.
        #
        #     assert "abcd"[2]         == 'c'
        redef fun [](index) do return _items[index]

        # Create a substring.
        #
        #     assert "abcd".substring(1, 2)      ==  "bc"
        #     assert "abcd".substring(-1, 2)     ==  "a"
        #     assert "abcd".substring(1, 0)      ==  ""
        #     assert "abcd".substring(2, 5)      ==  "cd"
        #
        # A `from` index < 0 will be replaced by 0.
        # Unless a `count` value is > 0 at the same time.
        # In this case, `from += count` and `count -= from`.
        fun substring(from: Int, count: Int): String
        do
                assert count >= 0
                count += from
                if from < 0 then from = 0
                if count > length then count = length
                if from < count then
                        var r = new Buffer.with_capacity(count - from)
                        while from < count do
                                r.push(_items[from])
                                from += 1
                        end
                        return r.to_s
                else
                        return ""
                end
        end

        # Create a substring from `self` beginning at the `from` position
        #
        #     assert "abcd".substring_from(1)    ==  "bcd"
        #     assert "abcd".substring_from(-1)   ==  "abcd"
        #     assert "abcd".substring_from(2)    ==  "cd"
        #
        # As with substring, a `from` index < 0 will be replaced by 0
        fun substring_from(from: Int): String
        do
                assert from < length
                return substring(from, length - from)
        end

        # Does self have a substring `str` starting from position `pos`?
        #
        #     assert "abcd".has_substring("bc",1)            ==  true
        #     assert "abcd".has_substring("bc",2)            ==  false
        fun has_substring(str: String, pos: Int): Bool
        do
                var itsindex = str.length - 1
                var myindex = pos + itsindex
                var myitems = _items
                var itsitems = str._items
                if myindex > length or itsindex > myindex  then return false
                var its_index_from = str._index_from
                itsindex += its_index_from
                while itsindex >= its_index_from do
                        if myitems[myindex] != itsitems[itsindex] then return false
                        myindex -= 1
                        itsindex -= 1
                end
                return true
        end

        # Is this string prefixed by `prefix`?
        #
        #     assert "abcd".has_prefix("ab")         ==  true
        #     assert "abcbc".has_prefix("bc")        ==  false
        fun has_prefix(prefix: String): Bool do return has_substring(prefix,0)

        # Is this string suffixed by `suffix`?
        #
        #     assert "abcd".has_suffix("abc")        ==  false
        #     assert "abcd".has_suffix("bcd")        ==  true
        fun has_suffix(suffix: String): Bool do return has_substring(suffix, length - suffix.length)

        # If `self` contains only digits, return the corresponding integer
        #
        #     assert "123".to_i        == 123
        #     assert "-1".to_i         == -1
        fun to_i: Int
        do
                # Shortcut
                return to_s.to_cstring.atoi
        end

        # If `self` contains a float, return the corresponding float
        #
        #     assert "123".to_f        == 123.0
        #     assert "-1".to_f         == -1.0
        #     assert "-1.2e-3".to_f    == -0.0012
        fun to_f: Float
        do
                # Shortcut
                return to_s.to_cstring.atof
        end

        # If `self` contains only digits and alpha <= 'f', return the corresponding integer.
        fun to_hex: Int do return a_to(16)

        # If `self` contains only digits and letters, return the corresponding integer in a given base
        #
        #     assert "120".a_to(3)     == 15
        fun a_to(base: Int) : Int
        do
                var i = 0
                var neg = false

                for c in self
                do
                        var v = c.to_i
                        if v > base then
                                if neg then
                                        return -i
                                else
                                        return i
                                end
                        else if v < 0 then
                                neg = true
                        else
                                i = i * base + v
                        end
                end
                if neg then
                        return -i
                else
                        return i
                end
        end

        # Returns `true` if the string contains only Numeric values (and one "," or one "." character)
        #
        #     assert "123".is_numeric  == true
        #     assert "1.2".is_numeric  == true
        #     assert "1,2".is_numeric  == true
        #     assert "1..2".is_numeric == false
        fun is_numeric: Bool
        do
                var has_point_or_comma = false
                for i in self
                do
                        if not i.is_numeric
                        then
                                if (i == '.' or i == ',') and not has_point_or_comma
                                then
                                        has_point_or_comma = true
                                else
                                        return false
                                end
                        end
                end
                return true
        end

        # A upper case version of `self`
        #
        #     assert "Hello World!".to_upper     == "HELLO WORLD!"
        fun to_upper: String
        do
                var s = new Buffer.with_capacity(length)
                for i in self do s.add(i.to_upper)
                return s.to_s
        end

        # A lower case version of `self`
        #
        #     assert "Hello World!".to_lower     == "hello world!"
        fun to_lower : String
        do
                var s = new Buffer.with_capacity(length)
                for i in self do s.add(i.to_lower)
                return s.to_s
        end

        # Trims trailing and preceding white spaces
        # A whitespace is defined as any character which ascii value is less than or equal to 32
        #
        #     assert "  Hello  World !  ".trim   == "Hello  World !"
        #     assert "\na\nb\tc\t".trim          == "a\nb\tc"
        fun trim: String
        do
                if self._length == 0 then return self.to_s
                # find position of the first non white space char (ascii < 32) from the start of the string
                var start_pos = 0
                while self[start_pos].ascii <= 32 do
                        start_pos += 1
                        if start_pos == _length then return ""
                end
                # find position of the first non white space char from the end of the string
                var end_pos = length - 1
                while self[end_pos].ascii <= 32 do
                        end_pos -= 1
                        if end_pos == start_pos then return self[start_pos].to_s
                end
                return self.substring(start_pos, end_pos - start_pos + 1)
        end

        redef fun output
        do
                var i = 0
                while i < length do
                        _items[i].output
                        i += 1
                end
        end

        # Mangle a string to be a unique string only made of alphanumeric characters
        fun to_cmangle: String
        do
                var res = new Buffer
                var underscore = false
                for c in self do
                        if (c >= 'a' and c <= 'z') or (c >='A' and c <= 'Z') then
                                res.add(c)
                                underscore = false
                                continue
                        end
                        if underscore then
                                res.append('_'.ascii.to_s)
                                res.add('d')
                        end
                        if c >= '0' and c <= '9' then
                                res.add(c)
                                underscore = false
                        else if c == '_' then
                                res.add(c)
                                underscore = true
                        else
                                res.add('_')
                                res.append(c.ascii.to_s)
                                res.add('d')
                                underscore = false
                        end
                end
                return res.to_s
        end

        # Escape " \ ' and non printable characters using the rules of literal C strings and characters
        #
        #     assert "abAB12<>&".escape_to_c         == "abAB12<>&"
        #     assert "\n\"'\\".escape_to_c         == "\\n\\\"\\'\\\\"
        fun escape_to_c: String
        do
                var b = new Buffer
                for c in self do
                        if c == '\n' then
                                b.append("\\n")
                        else if c == '\0' then
                                b.append("\\0")
                        else if c == '"' then
                                b.append("\\\"")
                        else if c == '\'' then
                                b.append("\\\'")
                        else if c == '\\' then
                                b.append("\\\\")
                        else if c.ascii < 32 then
                                b.append("\\{c.ascii.to_base(8, false)}")
                        else
                                b.add(c)
                        end
                end
                return b.to_s
        end
end

# Immutable strings of characters.
class String
        super Comparable
        super AbstractString
        super StringCapable

        redef type OTHER: String

        # Index in _items of the start of the string
        readable var _index_from: Int

        # Indes in _items of the last item of the string
        readable var _index_to: Int

        ################################################
        #       AbstractString specific methods        #
        ################################################

        redef fun [](index) do
                assert index >= 0
                # Check that the index (+ index_from) is not larger than indexTo
                # In other terms, if the index is valid
                assert (index + _index_from) <= _index_to
                return _items[index + _index_from]
        end

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

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

                var realFrom = _index_from + from

                if (realFrom + count) > _index_to then return new String.from_substring(realFrom, _index_to, _items)

                if count == 0 then return ""

                return new String.from_substring(realFrom, realFrom + count - 1, _items)
        end

        redef fun substring_from(from: Int): String
        do
                if from > _length then return ""
                if from < 0 then from = 0
                return substring(from, _length)
        end

        redef fun has_substring(str: String, pos: Int): Bool
        do
                var itsindex = str._length - 1

                var myindex = pos + itsindex
                var myitems = _items

                var itsitems = str._items

                if myindex > _length or itsindex > myindex then return false

                var itsindexfrom = str.index_from
                itsindex += itsindexfrom
                myindex += index_from

                while itsindex >= itsindexfrom do
                        if myitems[myindex] != itsitems[itsindex] then return false
                        myindex -= 1
                        itsindex -= 1
                end

                return true
        end

        redef fun to_upper: String
        do
                var outstr = calloc_string(self._length + 1)
                var out_index = 0

                var myitems = self._items
                var index_from = self._index_from
                var max = self._index_to

                while index_from <= max do
                        outstr[out_index] = myitems[index_from].to_upper
                        out_index += 1
                        index_from += 1
                end

                outstr[self.length] = '\0'

                return outstr.to_s_with_length(self._length)
        end

        redef fun to_lower : String
        do
                var outstr = calloc_string(self._length + 1)
                var out_index = 0

                var myitems = self._items
                var index_from = self._index_from
                var max = self._index_to

                while index_from <= max do
                        outstr[out_index] = myitems[index_from].to_lower
                        out_index += 1
                        index_from += 1
                end

                outstr[self.length] = '\0'

                return outstr.to_s_with_length(self._length)
        end

        redef fun trim: String
        do
                if self._length == 0 then return self
                # find position of the first non white space char (ascii < 32) from the start of the string
                var start_pos = self._index_from
                while _items[start_pos].ascii <= 32 do
                        start_pos += 1
                        if start_pos == _index_to + 1 then return ""
                end
                # find position of the first non white space char from the end of the string
                var end_pos = _index_to
                while _items[end_pos].ascii <= 32 do
                        end_pos -= 1
                        if end_pos == start_pos then return _items[start_pos].to_s
                end
                start_pos -= index_from
                end_pos -= index_from
                return self.substring(start_pos, end_pos - start_pos + 1)
        end

        redef fun output
        do
                var i = self._index_from
                var imax = self._index_to
                while i <= imax do
                        _items[i].output
                        i += 1
                end
        end

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

        # Creates a String object as a substring of another String
        #
        # From : index to start at
        #
        # To : Index to stop at (from + count -1)
        #
        private init from_substring(from: Int, to: Int, internalString: NativeString)
        do
                _items = internalString
                _index_from = from
                _index_to = to
                _length = to - from + 1
        end

        private init with_infos(items: NativeString, len: Int, from: Int, to: Int)
        do
                self._items = items
                _length = len
                _index_from = from
                _index_to = to
        end

        # Return a null terminated char *
        fun to_cstring: NativeString
        do
                if _index_from > 0 or _index_to != items.cstring_length - 1 then
                        var newItems = calloc_string(_length + 1)
                        self.items.copy_to(newItems, _length, _index_from, 0)
                        newItems[length] = '\0'
                        return newItems
                end
                return _items
        end

        redef fun ==(other)
        do
                if not other isa String or other is null then return false

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

                var my_length = _length

                if other._length != my_length then return false

                var my_index = _index_from
                var its_index = other._index_from

                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

        # The comparison between two strings is done on a lexicographical basis
        #
        #     assert ("aa" < "b")      ==  true
        redef fun <(other)
        do
                if self.object_id == other.object_id then return false

                var my_curr_char : Char
                var its_curr_char : Char

                var curr_id_self = self._index_from
                var curr_id_other = other._index_from

                var my_items = self._items
                var its_items = other._items

                var my_length = self._length
                var its_length = other._length

                var max_iterations = curr_id_self + my_length

                while curr_id_self < max_iterations do
                        my_curr_char = my_items[curr_id_self]
                        its_curr_char = its_items[curr_id_other]

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

                        curr_id_self += 1
                        curr_id_other += 1
                end

                return my_length < its_length
        end

        # The concatenation of `self` with `s`
        #
        #     assert "hello " + "world!"         == "hello world!"
        fun +(s: String): String
        do
                var my_length = self._length
                var its_length = s._length

                var total_length = my_length + its_length

                var target_string = calloc_string(my_length + its_length + 1)

                self._items.copy_to(target_string, my_length, _index_from, 0)
                s._items.copy_to(target_string, its_length, s._index_from, my_length)

                target_string[total_length] = '\0'

                return target_string.to_s_with_length(total_length)
        end

        # `i` repetitions of `self`
        #
        #     assert "abc"*3           == "abcabcabc"
        #     assert "abc"*1           == "abc"
        #     assert "abc"*0           == ""
        fun *(i: Int): String
        do
                assert i >= 0

                var my_length = self._length

                var final_length = my_length * i

                var my_items = self._items

                var target_string = calloc_string((final_length) + 1)

                target_string[final_length] = '\0'

                var current_last = 0

                for iteration in [1 .. i] do
                        my_items.copy_to(target_string, my_length, 0, current_last)
                        current_last += my_length
                end

                return target_string.to_s_with_length(final_length)
        end

        redef fun to_s do return self

        redef fun hash
        do
                # djb2 hash algorythm
                var h = 5381
                var i = _length - 1

                var myitems = _items
                var strStart = _index_from

                i += strStart

                while i >= strStart do
                        h = (h * 32) + h + self._items[i].ascii
                        i -= 1
                end

                return h
        end
end

# Mutable strings of characters.
class Buffer
        super AbstractString
        super Comparable
        super StringCapable
        super AbstractArray[Char]

        redef type OTHER: String

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

        redef fun add(c)
        do
                if _capacity <= length then enlarge(length + 5)
                _items[length] = c
                _length += 1
        end

        redef fun enlarge(cap)
        do
                var c = _capacity
                if cap <= c then return
                while c <= cap do c = c * 2 + 2
                var a = calloc_string(c+1)
                _items.copy_to(a, length, 0, 0)
                _items = a
                _capacity = c
        end

        redef fun append(s)
        do
                if s isa String then
                        var sl = s.length
                        if _capacity < _length + sl then enlarge(_length + sl)
                        s.items.copy_to(_items, sl, s._index_from, _length)
                        _length += sl
                else
                        super
                end
        end

        redef fun to_s: String
        do
                var l = length
                var a = calloc_string(l+1)
                _items.copy_to(a, l, 0, 0)

                # Ensure the afterlast byte is '\0' to nul-terminated char *
                a[length] = '\0'

                return a.to_s_with_length(length)
        end

        redef fun <(s)
        do
                var i = 0
                var l1 = length
                var l2 = s.length
                while i < l1 and i < l2 do
                        var c1 = self[i].ascii
                        var c2 = s[i].ascii
                        if c1 < c2 then
                                return true
                        else if c2 < c1 then
                                return false
                        end
                        i += 1
                end
                if l1 < l2 then
                        return true
                else
                        return false
                end
        end

        # Create a new empty string.
        init
        do
                with_capacity(5)
        end

        init from(s: String)
        do
                _capacity = s.length + 1
                _length = s.length
                _items = calloc_string(_capacity)
                s.items.copy_to(_items, _length, s._index_from, 0)
        end

        # Create a new empty string with a given capacity.
        init with_capacity(cap: Int)
        do
                assert cap >= 0
                # _items = new NativeString.calloc(cap)
                _items = calloc_string(cap+1)
                _capacity = cap
                _length = 0
        end

        redef fun ==(o)
        do
                if not o isa Buffer or o is null then return false
                var l = length
                if o.length != l then return false
                var i = 0
                var it = _items
                var oit = o._items
                while i < l do
                        if it[i] != oit[i] then return false
                        i += 1
                end
                return true
        end

        readable private var _capacity: Int
end

###############################################################################
# Refinement                                                                  #
###############################################################################

redef class Object
        # User readable representation of `self`.
        fun to_s: String do return inspect

        # The class name of the object in NativeString format.
        private fun native_class_name: NativeString is intern

        # The class name of the object.
        #
        #    assert 5.class_name == "Int"
        fun class_name: String do return native_class_name.to_s

        # Developer readable representation of `self`.
        # Usually, it uses the form "<CLASSNAME:#OBJECTID bla bla bla>"
        fun inspect: String
        do
                return "<{inspect_head}>"
        end

        # Return "CLASSNAME:#OBJECTID".
        # This function is mainly used with the redefinition of the inspect method
        protected fun inspect_head: String
        do
                return "{class_name}:#{object_id.to_hex}"
        end

        protected fun args: Sequence[String]
        do
                return sys.args
        end
end

redef class Bool
        #     assert true.to_s         == "true"
        #     assert false.to_s        == "false"
        redef fun to_s
        do 
                if self then 
                        return once "true" 
                else 
                        return once "false" 
                end
        end   
end

redef class Int
        # Fill `s` with the digits in base `base` of `self` (and with the '-' sign if 'signed' and negative).
        # assume < to_c max const of char
        fun fill_buffer(s: Buffer, base: Int, signed: Bool)
        do
                var n: Int
                # Sign
                if self < 0 then
                        n = - self
                        s[0] = '-'
                else if self == 0 then
                        s[0] = '0'
                        return
                else
                        n = self
                end
                # Fill digits
                var pos = digit_count(base) - 1
                while pos >= 0 and n > 0 do 
                        s[pos] = (n % base).to_c
                        n = n / base # /
                        pos -= 1
                end
        end

        # C function to convert an nit Int to a NativeString (char*)
        private fun native_int_to_s(len: Int): NativeString is extern "native_int_to_s"

        # return displayable int in base 10 and signed
        #
        #     assert 1.to_s            == "1"
        #     assert (-123).to_s       == "-123"
        redef fun to_s do
                var len = digit_count(10)
                return native_int_to_s(len).to_s_with_length(len)
        end

        # return displayable int in hexadecimal (unsigned (not now))
        fun to_hex: String do return to_base(16,false)

        # return displayable int in base base and signed
        fun to_base(base: Int, signed: Bool): String
        do
                var l = digit_count(base)
                var s = new Buffer.from(" " * l)
                fill_buffer(s, base, signed)
                return s.to_s
        end
end

redef class Float
        # Pretty print self, print needoed decimals up to a max of 3.
        redef fun to_s do
                var str = to_precision( 3 )
                var len = str.length
                for i in [0..len-1] do
                        var j = len-1-i
                        var c = str[j]
                        if c == '0' then
                                continue
                        else if c == '.' then
                                return str.substring( 0, j+2 )
                        else
                                return str.substring( 0, j+1 )
                        end
                end
                return str
        end

        # `self` representation with `nb` digits after the '.'.
        fun to_precision(nb: Int): String
        do
                if nb == 0 then return self.to_i.to_s
                var f = self
                for i in [0..nb[ do f = f * 10.0
                if self > 0.0 then
                        f = f + 0.5
                else
                        f = f - 0.5
                end
                var i = f.to_i
                if i == 0 then return "0.0"
                var s = i.to_s
                var sl = s.length
                if sl > nb then
                        var p1 = s.substring(0, s.length-nb)
                        var p2 = s.substring(s.length-nb, nb)
                        return p1 + "." + p2
                else
                        return "0." + ("0"*(nb-sl)) + s
                end
        end

        fun to_precision_native(nb: Int): String import NativeString::to_s `{
                int size;
                char *str;

                size = snprintf(NULL, 0, "%.*f", (int)nb, recv);
                str = malloc(size + 1);
                sprintf(str, "%.*f", (int)nb, recv );

                return NativeString_to_s( str );
        `}
end

redef class Char
        #     assert 'x'.to_s    == "x"
        redef fun to_s
        do
                var s = new Buffer.with_capacity(1)
                s[0] = self
                return s.to_s
        end

        # Returns true if the char is a numerical digit
        fun is_numeric: Bool
        do
                if self >= '0' and self <= '9'
                then
                        return true
                end
                return false
        end

        # Returns true if the char is an alpha digit
        fun is_alpha: Bool
        do
                if (self >= 'a' and self <= 'z') or (self >= 'A' and self <= 'Z') then return true
                return false
        end

        # Returns true if the char is an alpha or a numeric digit
        fun is_alphanumeric: Bool
        do
                if self.is_numeric or self.is_alpha then return true
                return false
        end
end

redef class Collection[E]
        # Concatenate elements.
        redef fun to_s
        do
                var s = new Buffer
                for e in self do if e != null then s.append(e.to_s)
                return s.to_s
        end

        # Concatenate and separate each elements with `sep`.
        #
        #     assert [1, 2, 3].join(":")         == "1:2:3"
        #     assert [1..3].join(":")            == "1:2:3"
        fun join(sep: String): String
        do
                if is_empty then return ""
                
                var s = new Buffer # Result

                # Concat first item
                var i = iterator
                var e = i.item
                if e != null then s.append(e.to_s)
                
                # Concat other items
                i.next
                while i.is_ok do
                        s.append(sep)
                        e = i.item
                        if e != null then s.append(e.to_s)
                        i.next
                end
                return s.to_s
        end
end

redef class Array[E]
        # Fast implementation
        redef fun to_s
        do
                var s = new Buffer
                var i = 0
                var l = length
                while i < l do
                        var e = self[i]
                        if e != null then s.append(e.to_s)
                        i += 1
                end
                return s.to_s
        end
end

redef class Map[K,V]
        # Concatenate couple of 'key value'.
        # key and value are separated by `couple_sep`.
        # each couple is separated each couple with `sep`.
        #
        #     var m = new ArrayMap[Int, String]
        #     m[1] = "one"
        #     m[10] = "ten"
        #     assert m.join("; ", "=") == "1=one; 10=ten"
        fun join(sep: String, couple_sep: String): String
        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
                if e != null then s.append("{k}{couple_sep}{e}")
                
                # Concat other items
                i.next
                while i.is_ok do
                        s.append(sep)
                        k = i.key
                        e = i.item
                        if e != null then s.append("{k}{couple_sep}{e}")
                        i.next
                end
                return s.to_s
        end
end

###############################################################################
# Native classes                                                              #
###############################################################################

# Native strings are simple C char *
class NativeString
        super StringCapable

        fun [](index: Int): Char is intern
        fun []=(index: Int, item: Char) is intern
        fun copy_to(dest: NativeString, length: Int, from: Int, to: Int) is intern

        # Position of the first nul character.
        fun cstring_length: Int
        do
                var l = 0
                while self[l] != '\0' do l += 1
                return l
        end
        fun atoi: Int is intern
        fun atof: Float is extern "atof"

        redef fun to_s
        do
                return to_s_with_length(cstring_length)
        end

        fun to_s_with_length(length: Int): String
        do
                assert length >= 0
                return new String.with_infos(self, length, 0, length - 1)
        end

        fun to_s_with_copy: String
        do
                var length = cstring_length
                var new_self = calloc_string(length + 1)
                copy_to(new_self, length, 0, 0)
                return new String.with_infos(new_self, length, 0, length - 1)
        end

end

# StringCapable objects can create native strings
interface StringCapable
        protected fun calloc_string(size: Int): NativeString is intern
end

redef class Sys
        var _args_cache: nullable Sequence[String]

        redef fun args: Sequence[String]
        do
                if _args_cache == null then init_args
                return _args_cache.as(not null)
        end

        # The name of the program as given by the OS
        fun program_name: String
        do
                return native_argv(0).to_s
        end

        # Initialize `args` with the contents of `native_argc` and `native_argv`.
        private fun init_args
        do
                var argc = native_argc
                var args = new Array[String].with_capacity(0)
                var i = 1
                while i < argc do
                        args[i-1] = native_argv(i).to_s
                        i += 1
                end
                _args_cache = args
        end

        # First argument of the main C function.
        private fun native_argc: Int is intern

        # Second argument of the main C function.
        private fun native_argv(i: Int): NativeString is intern
end