d3d3aa6 · urbit.org · git.iko.soy

git.iko.soy/urbit.org

on master help sign in

Merge pull request #1099 from urbit/roll-reel-revise

d3d3aa6poprox5 years ago

hoon/reference/stdlib/2b.md+60−9

compare with master

unifiedsplit

@@ -564,6 +564,11 @@ the final value of the accumulator.

564(To "slam" means to call a gate and give it a sample/samples. In this instance,

565`a` is the list of samples that are given to the gate b.)

566

567+The initial value of the accumulator is the bunt of `b`'s second argument (`+<+`). This can occasionally produce

568+undesired behavior (see examples). If you need more control over the initial

569+value, try making use of `$_` and `|:`, or perhaps [`+spin`](#spin) or

570+[`+spun`](#spun).

571+

567#### Accepts

572#### Accepts

568

573

569`a` is a list.

574`a` is a list.

@@ -600,6 +605,27 @@ The accumulator, which is a noun.

600 ! exit

605 ! exit

601```

606```

602

607

608+`+mul`'s default sample is 1, so calling `+reel` with `+mul` yields the expected behavior:

609+```

610+> *mul

611+1

612+

613+> (reel `(list @)`~[1 2 3 4] mul)

614+24

615+```

616+However, if you build a gate that uses `+mul` like so, the sample defaults to 0

617+since that is the bunt of `@`:

618+```

619+> (reel `(list @)`~[1 2 3 4] |=([a=@ b=@] (mul a b)))

620+0

621+```

622+We can fix this with `|:`:

623+```

624+> (reel `(list @)`~[1 2 3 4] |:([a=1 b=1] (mul a b)))

625+24

626+```

627+

628+

603

629

604---

630---

605### `++roll`

631### `++roll`

@@ -613,6 +639,11 @@ producing the final value of the accumulator.

613(To "slam" means to call a gate and give it a sample/samples. In this instance,

639(To "slam" means to call a gate and give it a sample/samples. In this instance,

614`a` is the list of samples that are given to the gate b.)

640`a` is the list of samples that are given to the gate b.)

615

641

642+The initial value of the accumulator is `b`'s second argument (`+<+`). This can

643+occasionally produce undesired behavior (see examples). If you need more control

644+over the initial value, try making use of `$_` and `|:`, or perhaps

645+[`+spin`](#spin) or [`+spun`](#spun).

646+

616#### Accepts

647#### Accepts

617

648

618`a` is a list.

649`a` is a list.

@@ -638,15 +669,35 @@ The accumulator, which is a noun.

638#### Examples

669#### Examples

639

670

640```

671```

641− > (roll `(list @)`[1 2 3 4 5 ~] add)

672+> (roll `(list @)`[1 2 3 4 5 ~] add)

642− q=15

673+q=15

643

674

644− > (roll `(list @)`[6 3 1 ~] sub)

675+> (roll `(list @)`[6 3 1 ~] sub)

645− ! subtract-underflow

676+! subtract-underflow

646− ! exit

677+! exit

678+

679+> (roll `(list @)`[1 3 6 ~] sub)

680+q=4

681+```

682+

683+`+mul`'s default sample is 1, so calling `+roll` with `+mul` yields the expected behavior:

684+```

685+> *mul

686+1

647

687

648− > (roll `(list @)`[1 3 6 ~] sub)

688+> (roll `(list @)`~[1 2 3 4] mul)

649− q=4

689+24

690+```

691+However, if you build a gate that uses `+mul` like so, the sample defaults to 0

692+since that is the bunt of `@`:

693+```

694+> (roll `(list @)`~[1 2 3 4] |=([a=@ b=@] (mul a b)))

695+0

696+```

697+We can fix this with `|:`:

698+```

699+> (roll `(list @)`~[1 2 3 4] |:([a=1 b=1] (mul a b)))

700+24

650```

701```

651

702

652

703

@@ -1042,7 +1093,7 @@ A list

1042

1093

1043

1094

1044---

1095---

1045−### `++spin`

1096+### `++spin` {#spin}

1046

1097

1047Gate to list, with state

1098Gate to list, with state

1048

1099

@@ -1107,7 +1158,7 @@ is the continuation of the RNG.

1107

1158

1108

1159

1109---

1160---

1110−### `++spun`

1161+### `++spun` {#spun}

1111

1162

1112Gate to list, with state

1163Gate to list, with state

1113

1164