| 1 | ---
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| 2 | default_highlighter: oils-sh
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| 3 | ---
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| 4 |
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| 5 | YSH Language Influences
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| 6 | =======================
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| 7 |
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| 8 | Almost all syntax in YSH comes from another language. This doc lists some of
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| 9 | these influences.
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| 10 |
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| 11 | Reading this page isn't essential for all users, but it may help some users
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| 12 | remember the syntax.
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| 13 |
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| 14 | <div id="toc">
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| 15 | </div>
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| 16 |
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| 17 | ## General Philosophy
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| 18 |
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| 19 | At a high level, YSH is a bash-compatible shell language that adds features
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| 20 | from popular dynamic languages.
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| 21 |
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| 22 | Its design is more conservative than that of other alternative shells. Our
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| 23 | goals are to:
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| 24 |
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| 25 | - **Preserve** what works best about shell: processes, pipelines, and files.
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| 26 | - **Clean up** the sharp edges like quoting, ad hoc parsing and splitting
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| 27 | - **Integrate** features from Python, JavaScript, Ruby, and other languages
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| 28 | listed below.
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| 29 |
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| 30 | ## Major Influences
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| 31 |
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| 32 | ### POSIX Shell
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| 33 |
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| 34 | The command and word syntax comes from shell:
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| 35 |
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| 36 | ls | wc -l # pipeline
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| 37 | echo $var "${var} $(hostname)" # variable and command sub
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| 38 | echo one; echo two # sequence of commands
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| 39 | test -d /tmp && test -d /tmp/foo # builtins and operators
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| 40 |
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| 41 | Shell-like extensions in YSH:
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| 42 |
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| 43 | echo $[42 + a[i]] # Expression substitution
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| 44 | cd /tmp { echo hi } # Block arguments
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| 45 |
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| 46 | ### bash and ksh
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| 47 |
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| 48 | We implement many bash semantics, like "named references" for out variables:
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| 49 |
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| 50 | f() {
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| 51 | local -n out=$1 # -n for named reference
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| 52 | out=bar
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| 53 | }
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| 54 |
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| 55 | x=foo
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| 56 | f x
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| 57 | echo x=$x # => x=bar
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| 58 |
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| 59 | Though we discourage dynamic scope. YSH provides a better mechanism called
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| 60 | `value.Place`.
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| 61 |
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| 62 | proc f(; out) {
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| 63 | call out->setValue('bar')
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| 64 | }
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| 65 |
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| 66 | var x = 'foo'
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| 67 | f (&x) # pass a place
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| 68 | echo x=$x # => x=bar
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| 69 |
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| 70 | <!--
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| 71 | Historical note: Usenix 93. korn shell was used for GUIs and such!
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| 72 | -->
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| 73 |
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| 74 | ### Python
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| 75 |
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| 76 | The YSH expression language is mostly Python compatible. Expressions occur on
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| 77 | the right-hand side of `=`:
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| 78 |
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| 79 | var a = 42 + a[i]
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| 80 | var b = fib(10)
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| 81 | var c = 'yes' if mybool else 'no'
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| 82 |
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| 83 | Proc signatures take influence from Python:
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| 84 |
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| 85 | proc mycopy(src, dest='/tmp') { # Python-like default value
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| 86 | cp --verbose $src $dest
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| 87 | }
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| 88 |
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| 89 | Related: differences documented in [YSH Expressions vs.
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| 90 | Python](ysh-vs-python.html).
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| 91 |
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| 92 | ### JavaScript
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| 93 |
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| 94 | YSH uses JavaScript's dict literals:
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| 95 |
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| 96 | var d1 = {name: 'Alice', age: 10} # Keys aren't quoted
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| 97 |
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| 98 | var d2 = {[mystr]: 'value'} # Key expressions in []
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| 99 |
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| 100 | var name = 'Bob'
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| 101 | var age = 15
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| 102 | var d3 = {name, age} # Omitted values taken from surrounding scope
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| 103 |
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| 104 | Blocks use curly braces, so most code resembles C / Java / JavaScript:
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| 105 |
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| 106 | if (x > 0) {
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| 107 | echo 'positive'
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| 108 | } else {
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| 109 | echo 'zero or negative'
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| 110 | }
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| 111 |
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| 112 | var i = 5
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| 113 | while (i > 0) {
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| 114 | echo $i
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| 115 | setvar i -= 1
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| 116 | }
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| 117 |
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| 118 | ### Ruby
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| 119 |
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| 120 | YSH has Ruby-like blocks:
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| 121 |
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| 122 | cd /tmp {
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| 123 | echo $PWD # prints /tmp
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| 124 | }
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| 125 | echo $PWD
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| 126 |
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| 127 | ### Perl
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| 128 |
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| 129 | The `@` character comes from Perl (and PowerShell):
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| 130 |
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| 131 | var myarray = :| one two three |
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| 132 | echo @myarray # @ is the "splice" operator
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| 133 |
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| 134 | echo @[arrayfunc(x, y)]
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| 135 |
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| 136 | for i in @(seq 3) { # split command sub
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| 137 | echo $i
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| 138 | }
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| 139 |
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| 140 | Perl can be viewed as a mixture of shell, awk, and sed. YSH is a similar
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| 141 | agglomeration of languages, but it's statically parsed.
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| 142 |
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| 143 | ### Julia
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| 144 |
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| 145 | The semicolon in `proc` and `func` definitions comes from Julia:
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| 146 |
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| 147 | func f(x, y; invert=false) {
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| 148 | if (invert) {
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| 149 | return (-x - y)
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| 150 | } else {
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| 151 | return (x + y)
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| 152 | }
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| 153 | }
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| 154 |
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| 155 | Multiline strings in YSH strip leading whitespace, similar to Julia:
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| 156 |
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| 157 | proc p {
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| 158 | # Because leading and trailing space are stripped, this is 2 lines long
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| 159 | var foods = '''
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| 160 | peanut
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| 161 | coconut
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| 162 | '''
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| 163 | }
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| 164 |
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| 165 |
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| 166 | (Julia has something like blocks too.)
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| 167 |
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| 168 | ### Go
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| 169 |
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| 170 | Like Go, Oils is UTF-8-centric. (Go blog: [Strings, bytes, runes and
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| 171 | characters in Go](https://go.dev/blog/strings).)
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| 172 |
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| 173 | The design of for loops is roughly influenced by Go:
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| 174 |
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| 175 | for i, item in (mylist) { # ask for index and value
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| 176 | echo "$i $item"
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| 177 | }
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| 178 |
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| 179 | for i, k, v in (mydict) { # ask for index, key, and value
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| 180 | echo "$i $k $v"
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| 181 | }
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| 182 |
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| 183 | ### Awk
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| 184 |
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| 185 | YSH gets its regex match operator from Awk:
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| 186 |
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| 187 | if (mystr ~ /digit+/) {
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| 188 | echo 'Number'
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| 189 | }
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| 190 |
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| 191 | (We don't use Perl's `=~` operator.)
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| 192 |
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| 193 | ### Lisp
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| 194 |
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| 195 | YSH has "quotation types" that represent unevaluated code. Like Lisp, they
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| 196 | give you control over evaluation:
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| 197 |
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| 198 | var my_cmd = ^(ls /tmp | wc -l)
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| 199 | eval (my_cmd)
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| 200 |
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| 201 | var my_expr = ^[42 + a[i]]
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| 202 | var v = evalExpr(my_expr)
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| 203 |
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| 204 | var my_template = ^"hi $name" # unimplemented
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| 205 |
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| 206 | ### Haskell
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| 207 |
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| 208 | YSH also uses `++` to concatenate strings and lists:
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| 209 |
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| 210 | var mystr = a ++ b
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| 211 | var mystr = "$a$b" # very similar
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| 212 |
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| 213 | var mylist = c ++ d
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| 214 | var mylist = :| @c @d | # also converts every element to a string
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| 215 |
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| 216 | YSH has a `value.IO` type that makes functions pure:
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| 217 |
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| 218 | func renderPrompt(io) {
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| 219 | return (io->promptVal('$') ++ " ")
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| 220 | }
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| 221 |
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| 222 | ## Minor Influences
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| 223 |
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| 224 | ### make, find and xargs
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| 225 |
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| 226 | Our design for Ruby-like blocks was influenced by these mini-languages.
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| 227 |
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| 228 | ### Tcl
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| 229 |
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| 230 | YSH uses `proc` and `setvar`, which makes it look something like Tcl:
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| 231 |
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| 232 | proc p(x) {
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| 233 | setvar y = x * 2
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| 234 | echo $y
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| 235 | }
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| 236 |
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| 237 | p 3 # prints 6
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| 238 |
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| 239 | But this is mostly superficial: YSH isn't homoiconic like Tcl is, and has a
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| 240 | detailed syntax. It intentionally avoids dynamic parsing.
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| 241 |
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| 242 | However, [Data Definition and Code Generation in Tcl (PDF)][config-tcl] shows
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| 243 | how Tcl can be used a configuration language:
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| 244 |
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| 245 | change 6/11/2003 {
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| 246 | author "Will Duquette"
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| 247 | description {
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| 248 | Added the SATl component to UCLO.
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| 249 | }
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| 250 | }
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| 251 |
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| 252 | Hay blocks in YSH allow this to be expressed very similarly:
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| 253 |
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| 254 | hay define Change
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| 255 |
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| 256 | Change 6/11/2003 {
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| 257 | author = "Will Duquette"
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| 258 | description = '''
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| 259 | Added the SATl component to UCLO.
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| 260 | '''
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| 261 | }
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| 262 |
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| 263 |
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| 264 | [config-tcl]: https://trs.jpl.nasa.gov/bitstream/handle/2014/7660/03-1728.pdf
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| 265 |
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| 266 | ### PHP
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| 267 |
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| 268 | PHP has global variables like `_REQUEST` and `_POST`.
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| 269 |
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| 270 | YSH has `_status`, `_group()`, `_start()`, etc. These are global variables
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| 271 | that are "silently" mutated by the interpreter (and functions to access such
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| 272 | global data).
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| 273 |
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| 274 | ### Lua
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| 275 |
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| 276 | YSH also uses a leading `=` to print expressions in the REPL.
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| 277 |
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| 278 | = 1 + 2
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| 279 |
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| 280 | Lua's implementation as a pure ANSI C core without I/O was also influential.
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| 281 |
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| 282 | ### C
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| 283 |
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| 284 | Most of our C-like syntax can be attributed to JavaScript or Python. But the
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| 285 | `value.Place` type is created with the `&` operator, and should be familiar to
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| 286 | C users:
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| 287 |
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| 288 | $ echo hi | read --all (&myvar)
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| 289 | $ echo "myvar=$myvar"
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| 290 | => myvar=hi
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| 291 |
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| 292 | So a `value.Place` behaves like a pointer in some ways.
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| 293 |
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| 294 | The `&` syntax may also feel familiar to Rust users.
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| 295 |
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| 296 | ## Related
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| 297 |
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| 298 | - [Novelties in OSH and YSH](novelties.html)
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| 299 |
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| 300 | <!--
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| 301 |
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| 302 | Config Dialect:
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| 303 |
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| 304 | - nginx configs?
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| 305 | - HCL?
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| 306 |
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| 307 | What about JS safe string interpolation?
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| 308 |
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| 309 | - r"foo"
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| 310 |
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| 311 | LATER:
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| 312 |
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| 313 | - R language (probably later, need help): data frames
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| 314 | - lazy evaluation like mutate (ms = secs * 100)
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| 315 |
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| 316 | Go for type signatures:
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| 317 |
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| 318 | func add(x Int, y Int) Int {
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| 319 | return x + y
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| 320 | }
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| 321 | # what about named return values?
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| 322 |
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| 323 | and MyPy for types like List[Int], Dict[Str, Str]
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| 324 |
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| 325 | (Swift and Perl 6 also capitalize all types)
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| 326 |
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| 327 | Rust:
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| 328 |
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| 329 | 0..n and 1..=n ?
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| 330 | enum
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| 331 | |x| x+1
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| 332 |
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| 333 | Clojure:
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| 334 |
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| 335 | \n and \newline for character literals, but YSH uses #'n' and \n
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| 336 |
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| 337 | maybe set literals with #{a b c} vs. #{a, b, c}
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| 338 |
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| 339 | ## Paradigms and Style
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| 340 |
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| 341 | Shell is already mix of:
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| 342 |
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| 343 | - dataflow: concurrent processes and files, pipelines
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| 344 | - instead of Clojure's "functions and data", we have "processes and files".
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| 345 | Simple. Functional. Transforming file system trees is a big part of
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| 346 | containers.
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| 347 | - imperative: the original Bourne shell added this.
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| 348 | - "functions" are really procedures; return
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| 349 | - iteration constructs: while / for / break / continue
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| 350 | - conditional constructs: if / case
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| 351 |
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| 352 | YSH is:
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| 353 |
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| 354 | - getting rid of: ksh. Bourne shell is good; ksh is bad because it adds bad
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| 355 | string operators.
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| 356 | - `${x%%a}` `${x//}` getting rid of all this crap. Just use functions.
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| 357 | - korn shell arrays suck. Replaced with python-like arrays
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| 358 | - Add Python STRUCTURED DATA.
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| 359 | - the problem with PROCESSES AND FILES is that it forces serialization everywhere.
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| 360 | - Structured Data in YSH
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| 361 | - Add **declarative** paradigm to shell.
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| 362 | - Package managers like Alpine Linux, Gentoo need declarative formats. So do
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| 363 | tools like Docker and Chef.
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| 364 | - Language-Oriented -- internal DSLs.
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| 365 | -->
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