Bob Nystrom
58e4d26648
Get rid of the separate opt-in IO class and replace it with a core System class. - Remove wren_io.c, wren_io.h, and io.wren. - Remove the flags that disable it. - Remove the overloads for print() with different arity. (It was an experiment, but I don't think it's that useful.) - Remove IO.read(). That will reappear using libuv in the CLI at some point. - Remove IO.time. Doesn't seem to have been used. - Update all of the tests, docs, etc. I'm sorry for all the breakage this causes, but I think "System" is a better name for this class (it makes it natural to add things like "System.gc()") and frees up "IO" for referring to the CLI's IO module.
104 lines
3.0 KiB
Markdown
104 lines
3.0 KiB
Markdown
^title Values
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^category types
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Values are the built-in object types that all other objects are composed of.
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They can be created through *literals*, expressions that evaluate to a value.
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All values are *immutable*—once created, they do not change. The number
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`3` is always the number `3`. The string `"frozen"` can never have its
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character array modified in place.
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## Booleans
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A boolean value represents truth or falsehood. There are two boolean literals,
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`true` and `false`. Their class is [Bool](core/bool.html).
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## Numbers
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Like other scripting languages, Wren has a single numeric type:
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double-precision floating point. Number literals look like you expect coming
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from other languages:
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:::dart
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0
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1234
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-5678
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3.14159
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1.0
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-12.34
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Numbers are instances of the [Num](core/num.html) class.
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## Strings
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A string is an array of bytes. Typically, they store characters encoded in
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UTF-8, but you can put any byte values in there, even zero or invalid UTF-8
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sequences. (You might have some trouble *printing* the latter to your terminal,
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though.)
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String literals are surrounded in double quotes:
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:::dart
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"hi there"
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A handful of escape characters are supported:
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:::dart
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"\0" // The NUL byte: 0.
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"\"" // A double quote character.
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"\\" // A backslash.
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"\a" // Alarm beep. (Who uses this?)
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"\b" // Backspace.
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"\f" // Formfeed.
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"\n" // Newline.
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"\r" // Carriage return.
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"\t" // Tab.
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"\v" // Vertical tab.
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A `\u` followed by four hex digits can be used to specify a Unicode code point:
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:::dart
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System.print("\u0041\u0b83\u00DE") // "AஃÞ"
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A `\x` followed by two hex digits specifies a single unencoded byte:
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System.print("\x48\x69\x2e") // "Hi."
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Strings are instances of class [String](core/string.html).
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## Ranges
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A range is a little object that represents a consecutive range of integers.
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They don't have their own dedicated literal syntax. Instead, the number class
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implements the `..` and `...` [operators](expressions.html#operators) to create
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them:
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:::dart
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3..8
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This creates a range from three to eight, including eight itself. If you want a
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half-inclusive range, use `...`:
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:::dart
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4...6
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This creates a range from four to six *not* including six itself. Ranges are
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commonly used for [iterating](control-flow.html#for-statements) over a
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sequences of numbers, but are useful in other places too. You can pass them to
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a [list](lists.html)'s subscript operator to return a subset of the list, for
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example:
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:::dart
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var list = ["a", "b", "c", "d", "e"]
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var slice = list[1..3]
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System.print(slice) // ["b", "c", "d"]
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Their class is [Range](core/range.html).
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## Null
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Wren has a special value `null`, which is the only instance of the class
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[Null](core/null.html). (Note the difference in case.) It functions a bit like
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`void` in some languages: it indicates the absence of a value. If you call a
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method that doesn't return anything and get its returned value, you get `null`
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back.
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