ec22aec · urbit.org · git.iko.soy

git.iko.soy/urbit.org

more clarifications

ec22aecJONATHAN PAPROCKI6 years ago

tutorials/hoon/arms-and-cores.md+20−12

@@ -99,7 +99,7 @@ First let's use the dojo to bind the face `a` to the value `12`, and the face `b

100Now use the following multi-line expression to bind `c` to a core. As before, feel free to cut and paste the following expression into the dojo (starting at `=c`):

101

102−```hoon

102+```

103> =c |%

104 ++ two 2

105 ++ inc (add 1 a)

@@ -215,7 +215,7 @@ The result is a tree of uncomputed Nock formulas. But you virtually never need

215

216To get the arm of a core to compute you must use its name. The arm names of `c` are in the expression used to create `c`:

217

218−```hoon

218+```

219> =c |%

220 ++ two 2

221 ++ inc (add 1 a)

@@ -490,14 +490,20 @@ Again, being able to read Nock is not essential to understanding Hoon.

490

491### Core Nesting

492

493+Let's take a quick look at how cores can be combined with `=>` to build up

493−Let's take a quick look at how cores can be combined with `=>` to build up larger structures. `=> p=hoon q=hoon` allows you to take the product of `q` with the product of `p` taken as the subject.

494+larger structures. `=> p=hoon q=hoon` yields the product of `q` with the product of `p` taken as the subject.

494

495

495−We can use this to set the context of cores. For example:

496+We can use this to set the context of cores. Recall that the payload of a gate

497+is a cell of `[sample context]`. For example:

496```

498```

497−~zod:dojo> =>([1 2] |=(@ 15))

499+~zod:dojo> =foo =>([1 2] |=(@ 15))

498−<1.fed {@ @ud @ud}>

500+> +3:foo

501+[0 1 2]

499```

502```

500−Here we have created a gate with `[1 2]` as its context that takes in an `@` and returns `15`.

503+Here we have created a gate with `[1 2]` as its context that takes in an `@` and

504+returns `15`. `+3:foo` shows the payload of the core to be `[0 [1 2]]`. Here `0`

505+is the default value of `@` and is the sample, while `[1 2]` is the context that

506+was given to `foo`.

501

507

502`=>` (and its reversed version `=<`) are used extensively to put cores into the

508`=>` (and its reversed version `=<`) are used extensively to put cores into the

503context of other cores.

509context of other cores.

@@ -516,8 +522,7 @@ context of other cores.

516```

522```

517At the level of arms, `+foo` is in the subject of `+bar`, and so `+bar` is able to call `+foo`. On the other hand, `+bar` is not in the subject of `+foo`, so `+foo` cannot call `+bar` - you will get a `-find.bar` error.

523At the level of arms, `+foo` is in the subject of `+bar`, and so `+bar` is able to call `+foo`. On the other hand, `+bar` is not in the subject of `+foo`, so `+foo` cannot call `+bar` - you will get a `-find.bar` error.

518

524

519−It is also helpful to think about what is happening on the level of cores here.

520−The `=>` here sets the context of the core containing `+bar` to be the core

525+At the level of cores, the `=>` sets the context of the core containing `+bar` to be the core

521containing `+foo`. Recall that arms are evaluated with the parent core as the

526containing `+foo`. Recall that arms are evaluated with the parent core as the

522subject. Thus `+bar` is evaluated with the core containing it as the subject,

527subject. Thus `+bar` is evaluated with the core containing it as the subject,

523which has the core containing `+foo` in its context. So this is why `+foo` is in

528which has the core containing `+foo` in its context. So this is why `+foo` is in

@@ -569,12 +574,13 @@ and so on, down to

569 $@(~ [~ u=item])

574 $@(~ [~ u=item])

570--

575--

571```

576```

572−This core contains the arms in parts [1a-1c of the standard library documentation](@/docs/reference/library/1a.md). If you count them, there are 41 arms in the core from `++ add` down to `++ unit`. We again can see this fact reflected in the Dojo by looking at the subject of `add`.

577+This core contains the arms in parts [1a-1c of the standard library documentation](@/docs/reference/library/1a.md). If you count them, there are 41 arms in the core from `++ add` down to `++ unit`. We again can see this fact reflected in the dojo by looking at the subject of `add`.

573```

578```

574> ..add

579> ..add

575<41.mac 1.ane $141>

580<41.mac 1.ane $141>

576```

581```

577−Now though, we see that the section 1 core is contained within the core containing `hoon-version`.

582+Here we see that core containing `hoon-version` is in the subject of the

583+section one core.

578

584

579Next, [section two](@/docs/reference/library/2a.md) starts:

585Next, [section two](@/docs/reference/library/2a.md) starts:

580```

586```

@@ -619,7 +625,9 @@ Lastly, let's check the subject of the last arm in `hoon.hoon` (as of November 2

619> ..pi-tell

625> ..pi-tell

620<92.nnn 247.tye 51.mvt 126.xjf 41.mac 1.ane $141>

626<92.nnn 247.tye 51.mvt 126.xjf 41.mac 1.ane $141>

621```

627```

622−This confirms for us, then, that `hoon.hoon` consists of six nested cores, with the `hoon-version` core at the top.

628+This confirms for us, then, that `hoon.hoon` consists of six nested cores, with one

629+inside the payload of the next, with

630+the `hoon-version` core most deeply nested.

623

631

624#### Exercise 1.7a

632#### Exercise 1.7a

625Pick a couple of arms in `hoon.hoon` and check to make sure that they are only

633Pick a couple of arms in `hoon.hoon` and check to make sure that they are only