module fp-0.0.1;

# Function composition
multi *infix:<o> (Code &f, Code &g) { sub($x) { f g $x } }
multi *infix:<∘> (Code &f, Code &g) { sub($x) { f g $x } }

# Haskell `...` metaoperator
multi *infix:<`map`>  (Code &f, *@y) { @y.map(&f) }
multi *infix:<`grep`> (Code &f, *@y) { @y.grep(&f) }

# Pair constructor
multi *infix:<⇒> ($x, $y) { $x => $y }

# Comparision ops
multi *infix:<≥> ($a, $b) { $a >= $b }
multi *infix:<≤> ($a, $b) { $a <= $b }
multi *infix:<≠> ($a, $b) { $a != $b }
multi *infix:<≣> ($a, $b) { $a === $b }
multi *infix:<≡> ($a, $b) { $a === $b }

# Misc. mathematical chars
multi *prefix:<∑>  ($nums) { [+] @$nums }
multi *prefix:<∏>  ($nums) { [*] @$nums }
multi *postfix:<!> ($x) { [*] 1..$x }
# multi ∞()       { Inf } -- doesn't work
multi *infix:<÷>   ($a, $b) { $a / $b }

# Standard functions of fp
sub identity($x)  is export { $x }
sub const($x)     is export { return -> $y { $x } }
sub tail(@array)  is export { @array[1...] }
sub init(@array)  is export { @array[0..@array.end-1] }

sub replicate(Int $n, Code &f) is export { (1..$n).map(&f) }

=head1 NAME

fp - Functional programming for Perl 6

=head1 SYNOPSIS

  use fp;

  (&say o &int)(10/3);               # 3
  (&say ∘ &int)(10/3);               # 3
  { $_ % 2 == 0 } `grep` [1,2,3,4];  # [2,4]
  { $_ * 2 } `map` [1,2,3];          # [2,4,6]
  my $pair = key ⇒ "value";

=head1 DESCRIPTION

This is an experimental module which eases the use of functional programming
techniques in Perl 6.

=head1 OPERATORS

=head2 C<< infix:<∘> (Code &f, Code &g) >>

Function composition, think of Haskell's C<.>. There's also the ASCII
equivalent C<o>.

=head2 C<< infix:<`map`> (Code &f, *@y) >>

=head2 C<< infix:<`grep`> (Code &f, *@y) >>

Infix versions of C<map> and C<grep>.

These will go when we can define own metaoperators (like C<[...]> or C<»...«>).
Then, all functions can be "infixized".

=head2 C<< infix:<⇒> ($key, $value) >>

Pair constructor (equivalent to C<< => >>).

=head2 C<≥>, C<≤>, C<≠>

Standard comparision operators.

=head2 C<≣>, C<≡>

Equivalent to C<===>.

=head2 C<< prefix:<∑>(@nums) >>, C<< prefix:<∏>(@nums) >>

Sum and product.

=head2 C<< postfix:<!>(Int $x) >>

Factorial.

=head1 FUNCTIONS

=head2 C<< identity($x) >>

The identity function.

=head2 C<< const($x) >>

Returns a new function which always returns C<$x>.

=head2 C<< tail(@array) >>

Returns all except the first element of C<@array>.

=head2 C<< init(@array) >>

Returns all except the last element of C<@array>.

=head2 C<< replicate(Int $n, Code &f) >>

Runs C<&f> C<$n> times and returns the results.

=head1 BUGS

This module is currently somewhat short, additions welcome! :)

=head1 AUTHOR

Ingo Blechschmidt E<lt>iblech@web.deE<gt>

=cut