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list

list

list -- feature used to define lists

list provides an abstract type for a sequence of elements of the same type.

A list sequence may be empty and contain no element, or it may have a fixed
or even an infinite number of elements.

The core of the implementation of an actual list lies in the implementation
of the actual Cons cell a non-empty list consists of.

Lists can typically be traversed using only immutable data. This makes them
more flexible than streams that require to store and update their state.

A list is immutable, so it can be reused and shared between threads.
Due to the nature of lists, in which many Cons cells are used, a list
may require more (heap) allocation than an array.

Functions

collect the contents of this list into an array

redefines:

create an array backed version of this sequence in case this is not array
backed. This will ensure that operations like index[] or drop perform
in constant time.

returns Sequence.this if is_array_backed.
Return this list as a list.

This is a helper function that needs to be defined because list is an heir
of Sequence.

redefines:

convenience feature to work around type inference issues
NYI remove when type inference gets better
§
:
Any
 => 
String 
[Inherited from  Sequence]
create a string representation of this Sequence including all the string
representations of its contents, separated by ',' and enclosed in '['
and ']'.

In case this Sequence is known to be `finite` or has at most (Sequence T).type
.AS_STRING_NON_FINITE_MAX_ELEMENTS elements, all elements will be shown in the
resulting string. Otherwise, only the first elements will be shown followed by
",…" as in "[1,2,3,4,5,6,7,8,9,10,…]".

To force printing of all elements of a finite `Sequence` for which `finite` is
false (which may be the case since a Sequence in general might not know that it
if finite), you may use `as_string_all`.

redefines:

§(sep String)
:
Any
 => 
String 
[Redefinition of Sequence.as_string]
create a string representation of this list including all the string
representations of its contents, separated by 'sep'.

redefines:

§
:
Any
 => 
String 
[Inherited from  Sequence]
create a string representation of this Sequence including all the string
representations of its contents, separated by ", " and enclosed in '['
and ']'.

NOTE: In case this Sequence is not finite, this will attempt to create an
infinitely long string resulting in failure due to resource exchaustion.
call 'as_string' on the elements
the arithmetic mean of the sequence
https://en.wikipedia.org/wiki/Arithmetic_mean
create a new list that contains the first elements of
this Sequence for which 'f e' is false
§(chunk_size i32)
:
Any
 => 
list (list Sequence.T) 
[Inherited from  Sequence]
chop this Sequence into chunks of `chunk_size`.
the last chunk may be smaller than `chunk_size`.
create a new Sequence from the result of applying 'f' to the
elements all combinations of elements of this Sequence and
all elements of 'b' iterating of 'b' repeatedly as follows

Sequence.this[0] , b[0]
Sequence.this[0] , b[1]
Sequence.this[0] , b[2]
Sequence.this[0] , ...
Sequence.this[0] , b.last
Sequence.this[1] , b[0]
Sequence.this[1] , b[1]
Sequence.this[1] , ...
... , ...
Sequence.this.last, b.last
create a new list from the result of applying 'f' to the
elements all combinations of elements of this list and
all elements of 'b' iterating of 'b' repeatedly as follows

list.this[0] , b[0]
list.this[0] , b[1]
list.this[0] , b[2]
list.this[0] , ...
list.this[0] , b.last
list.this[1] , b[0]
list.this[1] , b[1]
list.this[1] , ...
... , ...
list.this.last, b.last
Lazy list concatenation, O(1)
t is evaluated only when this list is exhausted

This is useful when doing buffered reading from an input
source and the next buffer chunk, the tail should only
be created when actually necessary.
List concatenation, O(count)
create a Sequence that consists of all the elements of this Sequence followed
by all the elements of s
§
:
Any
 => 
i32 
[Redefinition of Sequence.count]
count the elements of this list

redefines:

get the number of non-overlapping matches of l within this
get the number of matches of l
§
:
Any
 => 
list list.A 
[Redefinition of Sequence.cycle]
create a list that repeats the current list indefinitely. In case 'list.this'
is 'nil', returns 'nil'

redefines:

§(n i32)
:
Any
 => 
list list.A 
[Redefinition of Sequence.drop]
create a list from the tail of list.this dropping n elements (or fewer
if the list is shorter than n).

redefines:

Lazily drop the first elements of a list for which predicate 'p' holds.
§
:
Any
 => 
Type 
[Inherited from  Any]
Get the dynamic type of this instance. For value instances `x`, this is
equal to `type_of x`, but for `x` with a `ref` type `x.dynamic_type` gives
the actual runtime type, while `type_of x` results in the static
compile-time type.

There is no dynamic type of a type instance since this would result in an
endless hierarchy of types. So for Type values, dynamic_type is redefined
to just return Type.type.
§
:
Any
 => 
Sequence.T 
[Inherited from  Sequence]
the euclidean norm of this sequence
i.e. the square of the sum of squares of this sequence
Lazily filter the elements of a list.

The result contains exactly those elements for which p
is true.

redefines:

§(pattern Sequence Sequence.T)
:
Any
 => 
option i32 
[Inherited from  Sequence]
get the index of pattern within this Sequence or nil if it does not exist

uses the Knuth-Morris-Pratt algorithm
port of racket code from this paper:
https://www.cambridge.org/core/services/aop-cambridge-core/content/view/8EFA77D663D585B68630E372BCE1EBA4/S0956796824000017a.pdf/knuth-morris-pratt-illustrated.pdf

worst-case performance: O( seq_length ) + O( pattern_length )
worst-case space complexity: O( pattern_length )
§
:
Any
 => 
bool 
[Inherited from  Sequence]
is this sequence known to be finite? For infinite sequences, features like
count diverge.
§
:
Any
 => 
list.A 
[Redefinition of Sequence.first]
get the head of this list

list must not be empty, causes precondition failure if debug is enabled.

redefines:

§(default Sequence.T)
:
Any
 => 
Sequence.T 
[Inherited from  Sequence]
get the first element of this Sequence or default if sequence is empty
map each element of this Sequence to Sequence
Then flatten the result by one level,
essentially combining all the sequences.
map the list to a new list applying function f to all elements
and flatten the result of f in the process

This performs a lazy mapping, f is called only when the elements
are taken from the list.
§(m Monoid list.A)
:
Any
 => 
list.A 
[Redefinition of Sequence.fold]
fold the elements of this list using the given monoid.

e.g., to sum the elements of a list of i32, use l.fold i32.sum

redefines:

§(s list.A, m Monoid list.A)
:
Any
 => 
list.A
fold the elements of this list using the given monoid and initial value

Used to fold a list tail-recursively
fold the elements of this non-empty list using the given function

e.g., to find the minimum of a list of i32, use `l.fold1 (<=)`

redefines:

§(B 
type
, f Function list.foldf.B list.foldf.B list.A, e list.foldf.B)
:
Any
 => 
list.foldf.B 
[Redefinition of Sequence.foldf]
fold the elements of this list using the given function

e.g., to find the product of a list of i32, use `s.foldf (*) 1`

redefines:

call f in order on all elements of this list

redefines:

apply 'f' to each element 'e' as long as 'f e'
group the elements of this sequence by a key of type K

f determines the key of an element
get the head of this list if it exists, nil if it does
not exist
get a function that, given an index, returns the element at that index
§(i i32)
:
Any
 => 
Sequence.T 
[Inherited from  Sequence]
the nth element in the sequence, must exist
§(x Sequence.T)
:
Any
 => 
option i32 
[Inherited from  Sequence]
determine the index of element x within this list. 0 if x is at the
head of the list, 1 if it comes directly after head, etc. nil if x is
not in the list.
adds the corresponding index to
every element in the sequence
§(I 
type
, start_idx Sequence.indexed.I)
:
Any
 => 
list (tuple Sequence.indexed.I Sequence.T) 
[Inherited from  Sequence]
adds an index to every element
in the sequence starting at start_idx
consume all elements of this Sequence by f. This is an infix operator alias
for for_each.

Ex.: To print all the elements of a list, you can use

1..10 ! say
filter elements using predicate f, infix operator
synonym of filter.

NYI: What is better, 'infix |&' or 'infix &', or something else?
infix operand synonym for concat

redefines:

map the Sequence to a new Sequence applying function f to all elements

This is an infix operator alias of map enabling piping code like

l := 1..10 | *10 | 300-

to obtain 290,280,270,...200

Note that map and therefore also this operator is lazy, so

_ := (1..10 | say)

will not print anything while

(1..10 | say).for_each _->unit

will print the elements since `for_each` is not lazy.
filter elements using predicate f, infix operator
synonym of filter.
check if predicate f holds for all elements
check if predicate f holds for at least one element
returns the list of all but the last element of this list

list must not be empty, causes precondition failure if debug is enabled.
§(at i32, v Sequence.T)
:
Any
 => 
list Sequence.T 
[Inherited from  Sequence]
insert element v at position at
add an element sep between every element of this list.
apply transducer to sequence, returning a sequence of results

example usage:
human(age i32) is
ages := map (Sequence i32) human i32 (x -> x.age)
gt_ten := filter (Sequence i32) i32 (x -> x > 10)
xf := ages ∘ gt_ten
say ([human(4), human(12), human(30)].into xf) # [12,30]
§
:
Any
 => 
bool 
[Inherited from  Sequence]
is this Sequence known to be array backed? If so, this means that operations
like index[] are fast.
§
:
Any
 => 
bool 
[Redefinition of Sequence.is_empty]
is this list empty?

redefines:

§(i i32)
:
Any
 => 
bool 
[Inherited from  Sequence]
check if argument is a valid index in this sequence.

Note that this may have a performance in O(i) unless this
Sequence is_array_backed.
§
:
Any
 => 
list.A 
[Redefinition of Sequence.last]
get the last element of this list

list must not be empty, causes precondition failure if debug is enabled.

This may take time in O(count), in particular, it may not terminate
for an infinite list.

redefines:

§(default Sequence.T)
:
Any
 => 
Sequence.T 
[Inherited from  Sequence]
get the last element of this Sequence or default if sequence is empty
map the Sequence to a new Sequence applying function f to all elements

This performs a lazy mapping, f is called only when the elements
in the resulting list are accessed.
Map this Sequence to f applied to neighboring pairs of values
in this Sequence.

In case this Sequence has less than two elements, the result will
be the empty list.

ex. to obtain a list of differences you, you may use `map_pairs (-)`:

[2,3,5,7,11,13,17,19,23,29].map_pairs a,b->b-a

results in `[1,2,2,4,2,4,2,4,6]`
map the list to a new list applying function f to all elements

This performs a lazy mapping, f is called only when the elements
are taken from the list.
§
:
Any
 => 
option Sequence.T 
[Inherited from  Sequence]
maximum value in the sequence
§
:
Any
 => 
option Sequence.T 
[Inherited from  Sequence]
the median of the sequence
https://en.wikipedia.org/wiki/Median
§
:
Any
 => 
option Sequence.T 
[Inherited from  Sequence]
minimum value in the sequence
§(n i32)
:
Any
 => 
option Sequence.T 
[Inherited from  Sequence]
the nth element in the sequence if it exists, wrapped in an option,
nil otherwise.

Complexity: if Sequence is array backed O(1) otherwise O(n)
create a new Sequence from tuples of all combinations of elements
of this Sequence and all elements of 'b' iterating of 'b' repeatedly
as follows

(Sequence.this[0] , b[0] )
(Sequence.this[0] , b[1] )
(Sequence.this[0] , b[2] )
(Sequence.this[0] , ... )
(Sequence.this[0] , b.last)
(Sequence.this[1] , b[0] )
(Sequence.this[1] , b[1] )
(Sequence.this[1] , ... )
(... , ... )
(Sequence.this.last, b.last)
calls `f` for element in the Sequence.

Unlike `for_each` this returns itself
allowing easier composition with
other Sequence features.

example:
[1,2,3,4,5]
.filter is_prime
.peek say
.drop_while <10
§
:
Any
 => 
String 
[Inherited from  Any]
convenience prefix operator to create a string from a value.

This permits usage of `$` as a prefix operator in a similar way both
inside and outside of constant strings: $x and "$x" will produce the
same string.
add an element sep in front of every element of this list.
§(R 
type
, init Sequence.reduce.R, f Function (choice Sequence.reduce.R (abort Sequence.reduce.R)) Sequence.reduce.R Sequence.T)
:
Any
 => 
Sequence.reduce.R 
[Inherited from  Sequence]
reduce this Sequence to R with an initial value init
and a reducing function f.
the reduction is finished once f yields abort or
if the end of the sequence is reached.
reduce this Sequence to `outcome R`
with an initial value `init` and a reducing function `f`.
the reduction is finished once `f` yields `abort` or
if the end of the sequence is reached.
replace all occurrences of old by new
replace the first n occurrences of old by new
reverse the order of the elements in this Sequence
reverse the order of the elements in this list
map this Sequence to a list that contains the result of folding
all prefixes using the given monoid.

e.g., for a Sequence of i32 s, s.scan i32.sum creates a list of
partial sums (0..).map x->(s.take x).fold i32.sum

redefines:

map this Sequence to a list that contains the result of folding
all prefixes using the given monoid and initial value

Used to scan a list tail-recursively
§(from i32, to i32)
:
Any
 => 
Sequence Sequence.T 
[Inherited from  Sequence]
create a slice from this Sequence that consists of the elements starting at index
from (including) up to index to (excluding).
sort this Sequence using the total order defined by less_or_equal
sort this Sequence using total order defined for 'f a[i]'
create a tuple of two Sequences by splitting this at the given index, i.e.,
a Sequence of length 'at' and one of length 'count-at'.

at may be <= 0 or >= count, in which case the resulting tuple will be the
(empty list, Sequence.this.as_list) or (Sequence.this.as_list, empty list), resp.
does this sequence start with l?
the standard deviation of the sequence
https://en.wikipedia.org/wiki/Standard_deviation
get the tail of this list if it exists, nil if it does
not exist or it is the empty list
create a lazy list of all the tails of this list, including the complete list
'list.this' and the empty list 'nil'.

redefines:

§(n i32)
:
Any
 => 
list list.A 
[Redefinition of Sequence.take]
Lazily take the first n elements of a list, alternatively the whole list if it
is shorter than n, or the empty list if n <= 0

redefines:

Lazily take the first elements of a list for which predicate 'p' holds.
takes a transducer xf, a reducer f and an initial value
returns the result of applying the reducer xf f to the Sequence
the variance of the sequence
https://en.wikipedia.org/wiki/Variance
create a new list from the result of applying 'f' to the
elements of this list and 'b' in order.

redefines:

Type Features

§
:
Any
 is
 
[Inherited from  Type]
string representation of this type to be used for debugging.

result has the form "Type of '<name>'", but this might change in the future

redefines:

Maximum number of elements shown for on a call to `as_string` for a non-finite
Sequence.
monoid of Sequences with infix concatentation operation.
§
:
Any
 is
 
[Inherited from  Type]
There is no dynamic type of a type instance since this would result in an
endless hierarchy of types, so dynamic_type is redefined to just return
Type.type here.

redefines:

create an empty list
fmap lifts a function from A to B to a function from list A to list B
§(T 
type
)
:
Any
 is
 
[Inherited from  Type]
Is this type assignable to a type parameter with constraint `T`?

The result of this is a compile-time constant that can be used to specialize
code for a particular type.

is_of_integer_type(n T : numeric) => T : integer
say (is_of_integer_type 1234) # true
say (is_of_integer_type 3.14) # false

it is most useful in conjunction preconditions or `if` statements as in

pair(a,b T) is

=>

or

val(n T) is

monoid of lists with infix concatentation operation.

NYI: Name should be `concat_monoid`, we use `list_concat_monoid`
to avoid clash with inherited `Sequence.concat_monoid`. Maybe
the inherited one should be renamed once renaming is supported.
§
:
Any
 is
 
[Inherited from  Type]
name of this type, including type parameters, e.g. 'option (list i32)'.
§
:
Any
 is
 
[Inherited from  Any]
Get a type as a value.

This is a feature with the effect equivalent to Fuzion's `expr.type` call tail.
It is recommended to use `expr.type` and not `expr.type_value`.

`type_value` is here to show how this can be implemented and to illustrate the
difference to `dynamic_type`.