Add infix:<∘> to Operators

Author: tisonkun

doc/Language/operators.pod6

@@ -1164,10 +1164,46 @@ is returned.
 
 X<String concatenation operator>.
 
-Coerces both arguments to L<Str> and concatenates them. If both arguments are L<Buf>, a combined buffer is returned.
+Coerces both arguments to L<Str> and concatenates them. If both arguments are
+L<Buf|/type/Buf>, a combined buffer is returned.
 
     say 'ab' ~ 'c';     # OUTPUT: «abc␤»
 
+=head2 infix C«<∘>»
+
+    multi sub infix:<∘>()
+    multi sub infix:<∘>(&f)
+    multi sub infix:<∘>(&f, &g --> Block:D)
+
+X<Function combinator operator>
+
+The function composition operator C«infix:<∘>» or C«infix:<o>» combines two
+functions, so that the left function is called with the return value of the
+right function. If the L«C<.count>|/routine/count» of the left function is
+greater than 1, the return value of the right function will be
+L<slipped|/type/Slip> into the left function.
+
+Both C<.count> and C<.arity> of the RHS will be maintained.
+
+    sub f($p){ say 'f'; $p / 2 }
+    sub g($p){ say 'g'; $p * 2 }
+
+    my &composed = &f ∘ &g;
+    say composed 2; # OUTPUT: «g␤f␤2␤»
+    # equivalent to:
+    say 2.&g.&f;
+    # or to:
+    say f g 2;
+
+    =begin code
+    sub f($a, $b, $c) { [~] $c, $b, $a }
+    sub g($str){ $str.comb }
+    my &composed = &f ∘ &g;
+    say composed 'abc'; # OUTPUT: «cba␤»
+    # equivalent to:
+    say f |g 'abc';
+    =end code
+
 =head1 Junctive AND (all) Precedence
 
 =head2 infix C«&»

doc/Type/Callable.pod6

@@ -106,7 +106,6 @@ including L<Methods|/type/Method> and L<Blocks|/type/Block>:
 =head1 Operators
 
 =head2 C«infix:<∘>»
-X<|∘,function combinator>X<|o,function combinator>
 
 The function composition operator C«infix:<∘>» or C«infix:<o>» combines two functions, so
 that the left function is called with the return value of the right function.