| 1 | ---
|
| 2 | default_highlighter: oils-sh
|
| 3 | ---
|
| 4 |
|
| 5 | Guide to Procs and Funcs
|
| 6 | ========================
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| 7 |
|
| 8 | YSH has two major units of code: shell-like `proc`, and Python-like `func`.
|
| 9 |
|
| 10 | - Roughly speaking, procs are for commands and **I/O**, while funcs are for
|
| 11 | pure **computation**.
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| 12 | - Procs are often **big**, and may call **small** funcs. On the other hand,
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| 13 | it's possible, but rarer, for funcs to call procs.
|
| 14 | - You can write shell scripts **mostly** with procs, and perhaps a few funcs.
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| 15 |
|
| 16 | This doc compares the two mechanisms, and gives rough guidelines.
|
| 17 |
|
| 18 | <!--
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| 19 | See the blog for more conceptual background: [Oils is
|
| 20 | Exterior-First](https://www.oilshell.org/blog/2023/06/ysh-design.html).
|
| 21 | -->
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| 22 |
|
| 23 | <div id="toc">
|
| 24 | </div>
|
| 25 |
|
| 26 | ## Tip: Start Simple
|
| 27 |
|
| 28 | Before going into detail, here's a quick reminder that you don't have to use
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| 29 | **either** procs or funcs. YSH is a language that scales both down and up.
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| 30 |
|
| 31 | You can start with just a list of plain commands:
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| 32 |
|
| 33 | mkdir -p /tmp/dest
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| 34 | cp --verbose *.txt /tmp/dest
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| 35 |
|
| 36 | Then copy those into procs as the script gets bigger:
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| 37 |
|
| 38 | proc build-app {
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| 39 | ninja --verbose
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| 40 | }
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| 41 |
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| 42 | proc deploy {
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| 43 | mkdir -p /tmp/dest
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| 44 | cp --verbose *.txt /tmp/dest
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| 45 | }
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| 46 |
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| 47 | build-app
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| 48 | deploy
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| 49 |
|
| 50 | Then add funcs if you need pure computation:
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| 51 |
|
| 52 | func isTestFile(name) {
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| 53 | return (name => endsWith('._test.py'))
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| 54 | }
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| 55 |
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| 56 | if (isTestFile('my_test.py')) {
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| 57 | echo 'yes'
|
| 58 | }
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| 59 |
|
| 60 | ## At a Glance
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| 61 |
|
| 62 | ### Procs vs. Funcs
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| 63 |
|
| 64 | This table summarizes the difference between procs and funcs. The rest of the
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| 65 | doc will elaborate on these issues.
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| 66 |
|
| 67 | <style>
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| 68 | thead {
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| 69 | background-color: #eee;
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| 70 | font-weight: bold;
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| 71 | }
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| 72 | table {
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| 73 | font-family: sans-serif;
|
| 74 | border-collapse: collapse;
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| 75 | }
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| 76 |
|
| 77 | tr {
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| 78 | border-bottom: solid 1px;
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| 79 | border-color: #ddd;
|
| 80 | }
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| 81 |
|
| 82 | td {
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| 83 | padding: 8px; /* override default of 5px */
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| 84 | }
|
| 85 | </style>
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| 86 |
|
| 87 |
|
| 88 | <table>
|
| 89 |
|
| 90 | - thead
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| 91 | - <!-- empty -->
|
| 92 | - Proc
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| 93 | - Func
|
| 94 | - tr
|
| 95 | - Design Influence
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| 96 | - Shell-like.
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| 97 | - Python- and JavaScript-like, but **pure**.
|
| 98 | - tr
|
| 99 | - Shape
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| 100 | - Procs are shaped like Unix processes: with `argv`, an integer return code,
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| 101 | and `stdin` / `stdout` streams.
|
| 102 |
|
| 103 | They're a generalization of Bourne shell "functions".
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| 104 | - Funcs are shaped like mathematical functions.
|
| 105 | - tr
|
| 106 | - Architectural Role ([Oils is Exterior First](https://www.oilshell.org/blog/2023/06/ysh-design.html))
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| 107 | - **Exterior**: processes and files.
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| 108 | - **Interior**: functions and garbage-collected data structures.
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| 109 | - tr
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| 110 | - I/O
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| 111 | - Procs may start external processes and pipelines. Can perform I/O
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| 112 | anywhere.
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| 113 | - Funcs need an explicit `io` param to perform I/O.
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| 114 | - tr
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| 115 | - Example Definition
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| 116 | - ```
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| 117 | proc print-max (; x, y) {
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| 118 | echo $[x if x > y else y]
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| 119 | }
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| 120 | ```
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| 121 | - ```
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| 122 | func computeMax(x, y) {
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| 123 | return (x if x > y else y)
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| 124 | }
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| 125 | ```
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| 126 | - tr
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| 127 | - Example Call
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| 128 | - ```
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| 129 | print-max (3, 4)
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| 130 | ```
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| 131 |
|
| 132 | Procs can be put in pipelines:
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| 133 |
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| 134 | ```
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| 135 | print-max (3, 4) | tee out.txt
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| 136 | ```
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| 137 | - ```
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| 138 | var m = computeMax(3, 4)
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| 139 | ```
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| 140 |
|
| 141 | Or throw away the return value, which is useful for functions that mutate:
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| 142 |
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| 143 | ```
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| 144 | call computeMax(3, 4)
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| 145 | ```
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| 146 | - tr
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| 147 | - Naming Convention
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| 148 | - `kebab-case`
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| 149 | - `camelCase`
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| 150 | - tr
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| 151 | - [Syntax Mode](command-vs-expression-mode.html) of call site
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| 152 | - Command Mode</td>
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| 153 | - Expression Mode</td>
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| 154 | - tr
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| 155 | - Kinds of Parameters / Arguments
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| 156 | - <!-- empty -->
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| 157 | 1. Word aka string
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| 158 | 1. Typed and Positional
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| 159 | 1. Typed and Named
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| 160 | 1. Block
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| 161 |
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| 162 | Examples shown below.
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| 163 | - <!-- empty -->
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| 164 | 1. Positional
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| 165 | 1. Named
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| 166 |
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| 167 | (both typed)
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| 168 | - tr
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| 169 | - Return Value
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| 170 | - Integer status 0-255
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| 171 | - Any type of value, e.g.
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| 172 |
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| 173 | ```
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| 174 | return ([42, {name: 'bob'}])
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| 175 | ```
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| 176 | - tr
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| 177 | - Can it be a method on an object?
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| 178 | - No
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| 179 | - Yes, funcs may be bound to objects:
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| 180 |
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| 181 | ```
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| 182 | var x = obj.myMethod()
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| 183 | call obj->myMutatingMethod()
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| 184 | ```
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| 185 | - tr
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| 186 | - Interface Evolution
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| 187 | - **Slower**: Procs exposed to the outside world may need to evolve in a compatible or "versionless" way.
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| 188 | - **Faster**: Funcs may be refactored internally.
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| 189 | - tr
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| 190 | - Parallelism?
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| 191 | - Procs can be parallel with:
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| 192 | - shell constructs: pipelines, `&` aka `fork`
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| 193 | - external tools and the [$0 Dispatch
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| 194 | Pattern](https://www.oilshell.org/blog/2021/08/xargs.html): xargs, make,
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| 195 | Ninja, etc.
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| 196 | - Funcs are inherently **serial**, unless wrapped in a proc.
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| 197 | - tr
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| 198 | - More `proc` Features ...
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| 199 | <cell-attrs colspan=3 style="text-align: center; padding: 3em" />
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| 200 | - tr
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| 201 | - Kinds of Signature
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| 202 | - Open `proc p {` or <br/>
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| 203 | Closed `proc p () {`
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| 204 | - <!-- dash --> -
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| 205 | - tr
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| 206 | - Lazy Args
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| 207 | - ```
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| 208 | assert [42 === x]
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| 209 | ```
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| 210 | - <!-- dash --> -
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| 211 |
|
| 212 | </table>
|
| 213 |
|
| 214 | ### Func Calls and Defs
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| 215 |
|
| 216 | Now that we've compared procs and funcs, let's look more closely at funcs.
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| 217 | They're inherently **simpler**: they have 2 types of args and params, rather
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| 218 | than 4.
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| 219 |
|
| 220 | YSH argument binding is based on Julia, which has all the power of Python, but
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| 221 | without the "evolved warts" (e.g. `/` and `*`).
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| 222 |
|
| 223 | In general, with all the bells and whistles, func definitions look like:
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| 224 |
|
| 225 | # pos args and named args separated with ;
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| 226 | func f(p1, p2, ...rest_pos; n1=42, n2='foo', ...rest_named) {
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| 227 | return (len(rest_pos) + len(rest_named))
|
| 228 | }
|
| 229 |
|
| 230 | Func calls look like:
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| 231 |
|
| 232 | # spread operator ... at call site
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| 233 | var pos_args = [3, 4]
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| 234 | var named_args = {foo: 'bar'}
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| 235 | var x = f(1, 2, ...pos_args; n1=43, ...named_args)
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| 236 |
|
| 237 | Note that positional args/params and named args/params can be thought of as two
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| 238 | "separate worlds".
|
| 239 |
|
| 240 | This table shows simpler, more common cases.
|
| 241 |
|
| 242 |
|
| 243 | <table>
|
| 244 | <thead>
|
| 245 | <tr>
|
| 246 | <td>Args / Params</td>
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| 247 | <td>Call Site</td>
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| 248 | <td>Definition</td>
|
| 249 | </tr>
|
| 250 | </thead>
|
| 251 |
|
| 252 | <tr>
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| 253 | <td>Positional Args</td>
|
| 254 | <td>
|
| 255 |
|
| 256 | var x = myMax(3, 4)
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| 257 |
|
| 258 | </td>
|
| 259 | <td>
|
| 260 |
|
| 261 | func myMax(x, y) {
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| 262 | return (x if x > y else y)
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| 263 | }
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| 264 |
|
| 265 | </td>
|
| 266 | </tr>
|
| 267 |
|
| 268 | <tr>
|
| 269 | <td>Spread Pos Args</td>
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| 270 | <td>
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| 271 |
|
| 272 | var args = [3, 4]
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| 273 | var x = myMax(...args)
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| 274 |
|
| 275 | </td>
|
| 276 | <td>
|
| 277 |
|
| 278 | (as above)
|
| 279 |
|
| 280 | </td>
|
| 281 | </tr>
|
| 282 |
|
| 283 | <tr>
|
| 284 | <td>Rest Pos Params</td>
|
| 285 | <td>
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| 286 |
|
| 287 | var x = myPrintf("%s is %d", 'bob', 30)
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| 288 |
|
| 289 | </td>
|
| 290 | <td>
|
| 291 |
|
| 292 | func myPrintf(fmt, ...args) {
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| 293 | # ...
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| 294 | }
|
| 295 |
|
| 296 | </td>
|
| 297 | </tr>
|
| 298 |
|
| 299 | <tr>
|
| 300 | <td colspan=3 style="text-align: center; padding: 3em">...</td>
|
| 301 | </tr>
|
| 302 |
|
| 303 | </td>
|
| 304 | </tr>
|
| 305 |
|
| 306 | <tr>
|
| 307 | <td>Named Args</td>
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| 308 | <td>
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| 309 |
|
| 310 | var x = mySum(3, 4, start=5)
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| 311 |
|
| 312 | </td>
|
| 313 | <td>
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| 314 |
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| 315 | func mySum(x, y; start=0) {
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| 316 | return (x + y + start)
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| 317 | }
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| 318 |
|
| 319 | </td>
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| 320 | </tr>
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| 321 |
|
| 322 | <tr>
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| 323 | <td>Spread Named Args</td>
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| 324 | <td>
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| 325 |
|
| 326 | var opts = {start: 5}
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| 327 | var x = mySum(3, 4, ...opts)
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| 328 |
|
| 329 | </td>
|
| 330 | <td>
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| 331 |
|
| 332 | (as above)
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| 333 |
|
| 334 | </td>
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| 335 | </tr>
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| 336 |
|
| 337 | <tr>
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| 338 | <td>Rest Named Params</td>
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| 339 | <td>
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| 340 |
|
| 341 | var x = f(start=5, end=7)
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| 342 |
|
| 343 | </td>
|
| 344 | <td>
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| 345 |
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| 346 | func f(; ...opts) {
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| 347 | if ('start' not in opts) {
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| 348 | setvar opts.start = 0
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| 349 | }
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| 350 | # ...
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| 351 | }
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| 352 |
|
| 353 | </td>
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| 354 | </tr>
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| 355 |
|
| 356 | </table>
|
| 357 |
|
| 358 | ### Proc Calls and Defs
|
| 359 |
|
| 360 | Like funcs, procs have 2 kinds of typed args/params: positional and named.
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| 361 |
|
| 362 | But they may also have **string aka word** args/params, and a **block**
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| 363 | arg/param.
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| 364 |
|
| 365 | In general, a proc signature has 4 sections, like this:
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| 366 |
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| 367 | proc p (
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| 368 | w1, w2, ...rest_word; # word params
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| 369 | p1, p2, ...rest_pos; # pos params
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| 370 | n1, n2, ...rest_named; # named params
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| 371 | block # block param
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| 372 | ) {
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| 373 | echo 'body'
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| 374 | }
|
| 375 |
|
| 376 | In general, a proc call looks like this:
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| 377 |
|
| 378 | var pos_args = [3, 4]
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| 379 | var named_args = {foo: 'bar'}
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| 380 |
|
| 381 | p /bin /tmp (1, 2, ...pos_args; n1=43, ...named_args) {
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| 382 | echo 'block'
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| 383 | }
|
| 384 |
|
| 385 | The block can also be passed as an expression after a second semicolon:
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| 386 |
|
| 387 | p /bin /tmp (1, 2, ...pos_args; n1=43, ...named_args; block)
|
| 388 |
|
| 389 | <!--
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| 390 | - Block is really last positional arg: `cd /tmp { echo $PWD }`
|
| 391 | -->
|
| 392 |
|
| 393 | Some simpler examples:
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| 394 |
|
| 395 | <table>
|
| 396 | <thead>
|
| 397 | <tr>
|
| 398 | <td>Args / Params</td>
|
| 399 | <td>Call Site</td>
|
| 400 | <td>Definition</td>
|
| 401 | </tr>
|
| 402 | </thead>
|
| 403 |
|
| 404 | <tr>
|
| 405 | <td>Word args</td>
|
| 406 | <td>
|
| 407 |
|
| 408 | my-cd /tmp
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| 409 |
|
| 410 | </td>
|
| 411 | <td>
|
| 412 |
|
| 413 | proc my-cd (dest) {
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| 414 | cd $dest
|
| 415 | }
|
| 416 |
|
| 417 | </td>
|
| 418 | </tr>
|
| 419 |
|
| 420 | <tr>
|
| 421 | <td>Rest Word Params</td>
|
| 422 | <td>
|
| 423 |
|
| 424 | my-cd -L /tmp
|
| 425 |
|
| 426 | </td>
|
| 427 | <td>
|
| 428 |
|
| 429 | proc my-cd (...flags) {
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| 430 | cd @flags
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| 431 | }
|
| 432 |
|
| 433 | <tr>
|
| 434 | <td>Spread Word Args</td>
|
| 435 | <td>
|
| 436 |
|
| 437 | var flags = :| -L /tmp |
|
| 438 | my-cd @flags
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| 439 |
|
| 440 | </td>
|
| 441 | <td>
|
| 442 |
|
| 443 | (as above)
|
| 444 |
|
| 445 | </td>
|
| 446 | </tr>
|
| 447 |
|
| 448 | </td>
|
| 449 | </tr>
|
| 450 |
|
| 451 | <tr>
|
| 452 | <td colspan=3 style="text-align: center; padding: 3em">...</td>
|
| 453 | </tr>
|
| 454 |
|
| 455 | <tr>
|
| 456 | <td>Typed Pos Arg</td>
|
| 457 | <td>
|
| 458 |
|
| 459 | print-max (3, 4)
|
| 460 |
|
| 461 | </td>
|
| 462 | <td>
|
| 463 |
|
| 464 | proc print-max ( ; x, y) {
|
| 465 | echo $[x if x > y else y]
|
| 466 | }
|
| 467 |
|
| 468 | </td>
|
| 469 | </tr>
|
| 470 |
|
| 471 | <tr>
|
| 472 | <td>Typed Named Arg</td>
|
| 473 | <td>
|
| 474 |
|
| 475 | print-max (3, 4, start=5)
|
| 476 |
|
| 477 | </td>
|
| 478 | <td>
|
| 479 |
|
| 480 | proc print-max ( ; x, y; start=0) {
|
| 481 | # ...
|
| 482 | }
|
| 483 |
|
| 484 | </td>
|
| 485 | </tr>
|
| 486 |
|
| 487 | <tr>
|
| 488 | <td colspan=3 style="text-align: center; padding: 3em">...</td>
|
| 489 | </tr>
|
| 490 |
|
| 491 |
|
| 492 |
|
| 493 | <tr>
|
| 494 | <td>Block Argument</td>
|
| 495 | <td>
|
| 496 |
|
| 497 | my-cd /tmp {
|
| 498 | echo $PWD
|
| 499 | echo hi
|
| 500 | }
|
| 501 |
|
| 502 | </td>
|
| 503 | <td>
|
| 504 |
|
| 505 | proc my-cd (dest; ; ; block) {
|
| 506 | cd $dest (; ; block)
|
| 507 | }
|
| 508 |
|
| 509 | </td>
|
| 510 | </tr>
|
| 511 |
|
| 512 | <tr>
|
| 513 | <td>All Four Kinds</td>
|
| 514 | <td>
|
| 515 |
|
| 516 | p 'word' (42, verbose=true) {
|
| 517 | echo $PWD
|
| 518 | echo hi
|
| 519 | }
|
| 520 |
|
| 521 | </td>
|
| 522 | <td>
|
| 523 |
|
| 524 | proc p (w; myint; verbose=false; block) {
|
| 525 | = w
|
| 526 | = myint
|
| 527 | = verbose
|
| 528 | = block
|
| 529 | }
|
| 530 |
|
| 531 | </td>
|
| 532 | </tr>
|
| 533 |
|
| 534 | </table>
|
| 535 |
|
| 536 | ## Common Features
|
| 537 |
|
| 538 | Let's recap the common features of procs and funcs.
|
| 539 |
|
| 540 | ### Spread Args, Rest Params
|
| 541 |
|
| 542 | - Spread arg list `...` at call site
|
| 543 | - Rest params `...` at definition
|
| 544 |
|
| 545 | ### The `error` builtin raises exceptions
|
| 546 |
|
| 547 | The `error` builtin is idiomatic in both funcs and procs:
|
| 548 |
|
| 549 | func f(x) {
|
| 550 | if (x <= 0) {
|
| 551 | error 'Should be positive' (status=99)
|
| 552 | }
|
| 553 | }
|
| 554 |
|
| 555 | Tip: reserve such errors for **exceptional** situations. For example, an input
|
| 556 | string being invalid may not be uncommon, while a disk full I/O error is more
|
| 557 | exceptional.
|
| 558 |
|
| 559 | (The `error` builtin is implemented with C++ exceptions, which are slow in the
|
| 560 | error case.)
|
| 561 |
|
| 562 | ### Out Params: `&myvar` is of type `value.Place`
|
| 563 |
|
| 564 | Out params are more common in procs, because they don't have a typed return
|
| 565 | value.
|
| 566 |
|
| 567 | proc p ( ; out) {
|
| 568 | call out->setValue(42)
|
| 569 | }
|
| 570 | var x
|
| 571 | p (&x)
|
| 572 | echo "x set to $x" # => x set to 42
|
| 573 |
|
| 574 | But they can also be used in funcs:
|
| 575 |
|
| 576 | func f (out) {
|
| 577 | call out->setValue(42)
|
| 578 | }
|
| 579 | var x
|
| 580 | call f(&x)
|
| 581 | echo "x set to $x" # => x set to 42
|
| 582 |
|
| 583 | Observation: procs can do everything funcs can. But you may want the purity
|
| 584 | and familiar syntax of a `func`.
|
| 585 |
|
| 586 | ---
|
| 587 |
|
| 588 | Design note: out params are a nicer way of doing what bash does with `declare
|
| 589 | -n` aka `nameref` variables. They don't rely on [dynamic
|
| 590 | scope]($xref:dynamic-scope).
|
| 591 |
|
| 592 | ## Proc-Only Features
|
| 593 |
|
| 594 | Procs have some features that funcs don't have.
|
| 595 |
|
| 596 | ### Lazy Arg Lists `where [x > 10]`
|
| 597 |
|
| 598 | A lazy arg list is implemented with `shopt --set parse_bracket`, and is syntax
|
| 599 | sugar for an unevaluated `value.Expr`.
|
| 600 |
|
| 601 | Longhand:
|
| 602 |
|
| 603 | var my_expr = ^[42 === x] # value of type Expr
|
| 604 | assert (myexpr)
|
| 605 |
|
| 606 | Shorthand:
|
| 607 |
|
| 608 | assert [42 === x] # equivalent to the above
|
| 609 |
|
| 610 | ### Open Proc Signatures bind `argv`
|
| 611 |
|
| 612 | TODO: Implement new `ARGV` semantics.
|
| 613 |
|
| 614 | When a proc signature omits `()`, it's called **"open"** because the caller can
|
| 615 | pass "extra" arguments:
|
| 616 |
|
| 617 | proc my-open {
|
| 618 | write 'args are' @ARGV
|
| 619 | }
|
| 620 | # All valid:
|
| 621 | my-open
|
| 622 | my-open 1
|
| 623 | my-open 1 2
|
| 624 |
|
| 625 | Stricter closed procs:
|
| 626 |
|
| 627 | proc my-closed (x) {
|
| 628 | write 'arg is' $x
|
| 629 | }
|
| 630 | my-closed # runtime error: missing argument
|
| 631 | my-closed 1 # valid
|
| 632 | my-closed 1 2 # runtime error: too many arguments
|
| 633 |
|
| 634 |
|
| 635 | An "open" proc is nearly is nearly identical to a shell function:
|
| 636 |
|
| 637 | shfunc() {
|
| 638 | write 'args are' @ARGV
|
| 639 | }
|
| 640 |
|
| 641 | ## Methods are Funcs Bound to Objects
|
| 642 |
|
| 643 | Values of type `Obj` have an ordered set of name-value bindings, as well as a
|
| 644 | prototype chain of more `Obj` instances ("parents"). They support these
|
| 645 | operators:
|
| 646 |
|
| 647 | - dot (`.`) looks for attributes or methods with a given name.
|
| 648 | - Reference: [ysh-attr](ref/chap-expr-lang.html#ysh-attr)
|
| 649 | - Attributes may be in the object, or up the chain. They are returned
|
| 650 | literally.
|
| 651 | - Methods live up the chain. They are returned as `BoundFunc`, so that the
|
| 652 | first `self` argument of a method call is the object itself.
|
| 653 | - Thin arrow (`->`) looks for mutating methods, which have an `M/` prefix.
|
| 654 | - Reference: [thin-arrow](ref/chap-expr-lang.html#thin-arrow)
|
| 655 |
|
| 656 | ## The `__invoke__` method makes an Object "Proc-like"
|
| 657 |
|
| 658 | First, define a proc, with the first typed arg named `self`:
|
| 659 |
|
| 660 | proc myInvoke (word_param; self, int_param) {
|
| 661 | echo "sum = $[self.x + self.y + int_param]"
|
| 662 | }
|
| 663 |
|
| 664 | Make it the `__invoke__` method of an `Obj`:
|
| 665 |
|
| 666 | var methods = Object(null, {__invoke__: myInvoke})
|
| 667 | var invokable_obj = Object(methods, {x: 1, y: 2})
|
| 668 |
|
| 669 | Then invoke it like a proc:
|
| 670 |
|
| 671 | invokable_obj myword (3)
|
| 672 | # sum => 6
|
| 673 |
|
| 674 | ## Usage Notes
|
| 675 |
|
| 676 | ### 3 Ways to Return a Value
|
| 677 |
|
| 678 | Let's review the recommended ways to "return" a value:
|
| 679 |
|
| 680 | 1. `return (x)` in a `func`.
|
| 681 | - The parentheses are required because expressions like `(x + 1)` should
|
| 682 | look different than words.
|
| 683 | 1. Pass a `value.Place` instance to a proc or func.
|
| 684 | - That is, out param `&out`.
|
| 685 | 1. Print to stdout in a `proc`
|
| 686 | - Capture it with command sub: `$(myproc)`
|
| 687 | - Or with `read`: `myproc | read --all; echo $_reply`
|
| 688 |
|
| 689 | Obsolete ways of "returning":
|
| 690 |
|
| 691 | 1. Using `declare -n` aka `nameref` variables in bash.
|
| 692 | 1. Relying on [dynamic scope]($xref:dynamic-scope) in POSIX shell.
|
| 693 |
|
| 694 | ### Procs Compose in Pipelines / "Bernstein Chaining"
|
| 695 |
|
| 696 | Some YSH users may tend toward funcs because they're more familiar. But shell
|
| 697 | composition with procs is very powerful!
|
| 698 |
|
| 699 | They have at least two kinds of composition that funcs don't have.
|
| 700 |
|
| 701 | See #[shell-the-good-parts]($blog-tag):
|
| 702 |
|
| 703 | 1. [Shell Has a Forth-Like
|
| 704 | Quality](https://www.oilshell.org/blog/2017/01/13.html) - Bernstein
|
| 705 | chaining.
|
| 706 | 1. [Pipelines Support Vectorized, Point-Free, and Imperative
|
| 707 | Style](https://www.oilshell.org/blog/2017/01/15.html) - the shell can
|
| 708 | transparently run procs as elements of pipelines.
|
| 709 |
|
| 710 | <!--
|
| 711 |
|
| 712 | In summary:
|
| 713 |
|
| 714 | * func signatures look like JavaScript, Julia, and Go.
|
| 715 | * named and positional are separated with `;` in the signature.
|
| 716 | * The prefix `...` "spread" operator takes the place of Python's `*args` and `**kwargs`.
|
| 717 | * There are optional type annotations
|
| 718 | * procs are like shell functions
|
| 719 | * but they also allow you to name parameters, and throw errors if the arity
|
| 720 | is wrong.
|
| 721 | * and they take blocks.
|
| 722 |
|
| 723 | -->
|
| 724 |
|
| 725 | ## Summary
|
| 726 |
|
| 727 | YSH is influenced by both shell and Python, so it has both procs and funcs.
|
| 728 |
|
| 729 | Many programmers will gravitate towards funcs because they're familiar, but
|
| 730 | procs are more powerful and shell-like.
|
| 731 |
|
| 732 | Make your YSH programs by learning to use procs!
|
| 733 |
|
| 734 | ## Appendix
|
| 735 |
|
| 736 | ### Implementation Details
|
| 737 |
|
| 738 | procs vs. funcs both have these concerns:
|
| 739 |
|
| 740 | 1. Evaluation of default args at definition time.
|
| 741 | 1. Evaluation of actual args at the call site.
|
| 742 | 1. Arg-Param binding for builtin functions, e.g. with `typed_args.Reader`.
|
| 743 | 1. Arg-Param binding for user-defined functions.
|
| 744 |
|
| 745 | So the implementation can be thought of as a **2 × 4 matrix**, with some
|
| 746 | code shared. This code is mostly in [ysh/func_proc.py]($oils-src).
|
| 747 |
|
| 748 | ### Related
|
| 749 |
|
| 750 | - [Variable Declaration, Mutation, and Scope](variables.html) - in particular,
|
| 751 | procs don't have [dynamic scope]($xref:dynamic-scope).
|
| 752 | - [Block Literals](block-literals.html) (in progress)
|
| 753 |
|
| 754 | <!--
|
| 755 | TODO: any reference topics?
|
| 756 | -->
|
| 757 |
|
| 758 | <!--
|
| 759 | OK we're getting close here -- #**language-design>Unifying Proc and Func Params**
|
| 760 |
|
| 761 | I think we need to write a quick guide first, not a reference
|
| 762 |
|
| 763 |
|
| 764 | It might have some **tables**
|
| 765 |
|
| 766 | It might mention concerete use cases like the **flag parser** -- #**oil-dev>Progress on argparse**
|
| 767 |
|
| 768 |
|
| 769 | ### Diff-based explanation
|
| 770 |
|
| 771 | - why not Python -- because of `/` and `*` special cases
|
| 772 | - Julia influence
|
| 773 | - lazy args for procs `where` filters and `awk`
|
| 774 | - out Ref parameters are for "returning" without printing to stdout
|
| 775 |
|
| 776 | #**language-design>N ways to "return" a value**
|
| 777 |
|
| 778 |
|
| 779 | - What does shell have?
|
| 780 | - it has blocks, e.g. with redirects
|
| 781 | - it has functions without params -- only named params
|
| 782 |
|
| 783 |
|
| 784 | - Ruby influence -- rich DSLs
|
| 785 |
|
| 786 |
|
| 787 | So I think you can say we're a mix of
|
| 788 |
|
| 789 | - shell
|
| 790 | - Python
|
| 791 | - Julia (mostly subsumes Python?)
|
| 792 | - Ruby
|
| 793 |
|
| 794 |
|
| 795 | ### Implemented-based explanation
|
| 796 |
|
| 797 | - ASDL schemas -- #**oil-dev>Good Proc/Func refactoring**
|
| 798 |
|
| 799 |
|
| 800 | ### Big Idea: procs are for I/O, funcs are for computation
|
| 801 |
|
| 802 | We may want to go full in on this idea with #**language-design>func evaluator without redirects and $?**
|
| 803 |
|
| 804 |
|
| 805 | ### Very Basic Advice, Up Front
|
| 806 |
|
| 807 |
|
| 808 | Done with #**language-design>value.Place, & operator, read builtin**
|
| 809 |
|
| 810 | Place works with both func and proc
|
| 811 |
|
| 812 |
|
| 813 | ### Bump
|
| 814 |
|
| 815 | I think this might go in the backlog - #**blog-ideas**
|
| 816 |
|
| 817 |
|
| 818 | #**language-design>Simplify proc param passing?**
|
| 819 |
|
| 820 | -->
|
| 821 |
|
| 822 | <!-- vim sw=2 -->
|