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Clarify when do runs a block #4532

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Nov 24, 2024
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Clarify when do runs a block #4532

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Clarify when `do` runs a block
codesections Nov 13, 2024
df3b530
Update doc/Language/control.rakudoc
dontlaugh Nov 24, 2024
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12 changes: 12 additions & 0 deletions doc/Language/control.rakudoc
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Expand Up @@ -148,6 +148,18 @@ parenthesize a statement if it is the last thing in an expression:
=for code :skip-test<syntax error>
3, if 1 { 2 } ; # Syntax error

As a consequence, C<do> does not run blocks that, by their syntax, must
be functions. For example, if C«->» is used to specify a
L<signature|/language/syntax#Block_declaration>, C<do> treats these as
single-expression statements.

Thus, adding C«->» to our first example prevents the closure from
being evaluated:

=for code
# This never dies and never prints "Heads I win, tails I die."
do -> { say "Heads I win, tails I die."; Bool.pick } or die; say "I win.";

=head1 X<start|Control flow,start>

The simplest way to run a statement or block B<asynchronously> is by writing C<start>
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