mirror of
https://github.com/ilyakooo0/urbit.git
synced 2024-12-24 07:26:51 +03:00
133 lines
4.4 KiB
Markdown
133 lines
4.4 KiB
Markdown
<div class="short">
|
|
|
|
Runes
|
|
=====
|
|
|
|
In Hoon there are no reserved words. Instead, [`++twigs`]() (abstract
|
|
syntax trees), are formed using a diagraph of two ASCII symbols, which
|
|
is called a rune.
|
|
|
|
Runes are loosely divided into categories by their first character. To
|
|
find documentation on each individual category, follow these links:
|
|
|
|
<list></list>
|
|
|
|
<search/>
|
|
|
|
</div>
|
|
|
|
------------------------------------------------------------------------
|
|
|
|
Introduction
|
|
------------
|
|
|
|
For example, the rune `?:`, pronounced "wutcol", is a rune that accepts
|
|
three `++twig` expressions to form an "if-then-else statement," where
|
|
`p` is the predicate, `q` is the "then" statement, and `r` is the "else"
|
|
statement:
|
|
|
|
[%wtcl p=twig q=twig r=twig]
|
|
|
|
In a program, it is used like so:
|
|
|
|
++ add
|
|
|= [a=@ b=@]
|
|
^- @
|
|
?: =(0 a) b
|
|
$(a (dec a), b +(b))
|
|
|
|
Here the `=(0 a)` is `p`, the `b` is `q`, and the bottom line is the
|
|
`r`.
|
|
|
|
There are several benefits to using runes in lieu of reserved words.
|
|
First, it prevents the programmer from accidentally misusing a reserved
|
|
word as a variable name, which also allows her to be sure that any word
|
|
in her progam is an identifier. Next, as the first ASCII symbol of the
|
|
rune digraphs bears semantic significance, the programmer can look at
|
|
any rune and immediately have a basic, intuitive understanding as to
|
|
what it does.
|
|
|
|
Next, rune syntax addresses several issues that arise in other
|
|
languages. First, it produces cleaner, less verbose code that
|
|
conveniently flows downward. To highlight the verbosity Hoon avoids by
|
|
implementing runes, here is the C equivalent of the `++add` source code
|
|
printed above:
|
|
|
|
attribute add {
|
|
function(left-operand: atom, right-operand: atom)
|
|
produce atom
|
|
if equals(0, left-operand) {
|
|
right-operand
|
|
} else {
|
|
recurse(left-operand (decrement left-operand)),
|
|
right-operand (increment right-operand))
|
|
}
|
|
}
|
|
|
|
What is more, Hoon solves two problems that arise in functional
|
|
programming languages with very deep expression trees: first, the
|
|
collection of huge piles of closing parens at the end of large blocks;
|
|
and second, the fact that the depth of expression trees are thus bounded
|
|
by the width of the text box, as subexpressions tend to be indented.
|
|
Some languages solve the bracket-terminator problem by parsing
|
|
whitespace in order to use indentation to express tree depth:
|
|
|
|
?:
|
|
&
|
|
47
|
|
52
|
|
|
|
While this is actually valid Hoon, it does not solve the width problem.
|
|
|
|
To address this problem, most Hoon `++twigs` have a short, fixed
|
|
fan-out. Thus, the parser does not need significant whitespace nor a
|
|
terminator to determine how many twigs follow a `?:`--it already knows
|
|
that the answer is three. A smart parser allows the Hoon programmer to
|
|
format her code using a [backstep pattern]() that allows her to descend
|
|
into a deep tree without losing right margin.
|
|
|
|
Lastly, but perhaps most significantly, code is meant to be seen, and
|
|
not read. Anyone who has even slight experience coding Hoon will tell
|
|
you that they can understand and connect with properly formatted Hoon
|
|
code on a deeper, more intuitive level that cannot be explained but must
|
|
be experienced. One doesn't read `++add`, she sees it.
|
|
|
|
Names and Categories
|
|
--------------------
|
|
|
|
While the second glyph in a rune means little or nothing, the first
|
|
defines a rough semantic category:
|
|
|
|
| bar Core construction
|
|
$ buc Tile construction
|
|
% cen Invocations
|
|
: col Tuple construction
|
|
. dot Nock operations
|
|
# hax Pretty printing
|
|
^ ket Type conversions
|
|
; sem Composers (and XML generators)
|
|
~ sig Hints
|
|
= tis Subject modifiers
|
|
? wut Conditionals, booleans, and tests
|
|
! zap Special operations
|
|
|
|
As shown above, each glyph has its own monosyllabic name, designed to be
|
|
pronounced quickly in combination with another glyph to form a rune
|
|
name. As languages are often read-aloud, this saves the programmer from
|
|
having to say "dollar sign, question mark"--"bucwut" is much more
|
|
compact.
|
|
|
|
Irregular pronuncations
|
|
-----------------------
|
|
|
|
To avoid a few tongue-twisters, some runes have irregular pronunciations
|
|
that should be noted:
|
|
|
|
-- hephep phep
|
|
+- lushep slep
|
|
++ luslus slus
|
|
== tistis stet
|
|
|
|
Note: these runes are not members of any of the categories above, but
|
|
are mostly used to....
|