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179 lines
7.0 KiB
Markdown
179 lines
7.0 KiB
Markdown
---
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layout: developer-doc
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title: Literals
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category: syntax
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tags: [syntax, literals]
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order: 5
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---
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# Literals
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Enso supports a small set of literals that allow the expression of some common
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types in literal form in the source code.
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<!-- MarkdownTOC levels="2,3" autolink="true" -->
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- [Numeric Literals](#numeric-literals)
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- [Text Literals](#text-literals)
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- [Inline Text Literals](#inline-text-literals)
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- [Text Block Literals](#text-block-literals)
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- [Inline Block Literals](#inline-block-literals)
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- [Escape Sequences](#escape-sequences)
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- [Vector Literals](#vector-literals)
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<!-- /MarkdownTOC -->
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## Numeric Literals
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Enso provides rich support for numeric literals, including literals that use
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different numeric bases. It does, of course, support floating point numerals as
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well.
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A numeric literal takes the form:
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```ebnf
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digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
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hex = "a" | "b" | "c" | "d" | "e" | "f";
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number-digit = digit | hex;
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decimal-point = ".";
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float-digit = number-digit | decimal-point;
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base-specifier = { digit };
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numeric-literal = [base-specifier, "_"], { number-digit };
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```
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If no base is specified, it is inferred to be a standard base-10 numeral.
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Some examples of numeric literals follow:
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```ruby
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decimal = 12345.39
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decimal_explicit = 10_1029301
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octal = 8_122137
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hex = 16_ae2f14
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binary = 2_10011101010
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```
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> Actionables for this section are:
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>
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> - Think about whether we want to support explicit fractional and complex
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> literals, or whether these should be relegated to type constructors.
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## Text Literals
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Enso provides rich support for textual literals in the language, supporting both
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raw and interpolated strings natively.
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- **Raw Strings:** Raw strings are delimited using the standard double-quote
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character (`"`). Raw strings don't support any escape sequences.
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```ruby
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raw_string = "Hello, world!"
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```
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- **Interpolated Strings:** Interpolated strings support the splicing of
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executable Enso expressions into the string. Such strings are delimited using
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the single-quote (`'`) character, and splices are delimited using the backtick
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(`` ` ``) character. Splices are run, and then the result is converted to a
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string using `show`. These strings also have support for all kinds of
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[escape sequences](#escape-sequences).
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```ruby
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fmt_string = 'Hello, my age is `time.now.year - person.birthday.year`'
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```
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### Inline Text Literals
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In Enso, inline text literals are opened and closed using the corresponding
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quote type for the literal. They may contain escape sequences but may _not_ be
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broken across lines.
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```ruby
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inline_raw = "Foo bar baz"
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inline_interpolated = 'Foo `bar` baz'
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```
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### Text Block Literals
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In Enso, text block literals rely on _layout_ to determine the end of the block,
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allowing users to only _open_ the literal. Block literals are opened with three
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of the relevant quote type, and the contents of the block are determined by the
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following layout rules:
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- The first child line of the block sets the baseline left margin for the block.
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Any indentation up to this margin will be removed.
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- Any indentation further than this baseline will be retained as part of the
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text literal.
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- The literal is _closed_ by the first line with a _lower_ level of indentation
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than the first child line and will not contain the final blank line.
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```
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block_raw = '''
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part of the string
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still part of the string
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also part of the string
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not_string_expr = foo bar
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```
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### Inline Block Literals
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In order to easily transition between using text blocks and single-line
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literals, we allow for defining an inline block literal. This is a literal that
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uses the same start delimiter as a block literal (see above), but rather than
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ending the literal through de-indenting from the block's level of indentation,
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the literal is ended upon the line ending.
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```
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inline_block =
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"""this is all part of the literal
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but_this_is_not
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```
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### Escape Sequences
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Format literals in Enso support many kinds of escape sequence. These are
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described below.
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| Name | Escape Sequence | Unicode | Notes |
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| :----------- | :-------------: | :--------: | :---------------------------------------------------------------------------------------- |
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| Byte Escape | `\x##` | `U+00##` | 8-bit character specification. |
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| U16 Escape | `\u####` | `U+####` | 16-bit unicode character, where each `#` is a hex digit. |
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| U21 Escape | `\u{######}` | `U+######` | 21-bit unicode character, where `######` is 1-6 hex digits. |
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| U32 Escape | `\U########` | `U+######` | 32-bit unicode character, where each `#` is a hex digit and the first two bytes are `00`. |
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| Null | `\0` | `U+0000` | The null character. |
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| Alert | `\a` | `U+0007` | The bell/alert character. |
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| Backspace | `\b` | `U+0008` | The backspace character. |
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| Form Feed | `\f` | `U+000C` | The form-feed character. |
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| LF | `\n` | `U+000A` | The line-feed character (newline on unix systems). |
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| CR | `\r` | `U+000D` | The carriage return character (part of newline on windows systems). |
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| Tab | `\t` | `U+0009` | The horizontal tab character. |
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| Vertical Tab | `\v` | `U+000B` | The vertical tab character. |
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| Backslash | `\\` | `U+005C` | A literal backslash character. |
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| Double Quote | `\"` | `U+0022` | A literal double quote character. |
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| Single Quote | `\'` | `U+0027` | A literal single quote character. |
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| Backtick | `` \` `` | `U+0060` | A literal backtick character. |
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The only one of the above escape sequences that is supported in a raw text
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literal is `\"`. All other occurrences of `\` in such literals are treated as a
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literal backslash.
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## Vector Literals
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Enso also supports vector literals, which allow users to create literal vectors
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of elements.
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```ruby
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literal = [elem_1, elem_2, elem_3, ...]
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```
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A vector literal works as follows:
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- It is begun by the `[` character.
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- It is ended by the `]` character.
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- Elements in vector literals are concatenated using the `,` operator, which
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acts as `cons` on vectors.
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