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.
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^title Values ^category types
Values are the built-in object types that all other objects are composed of.
They can be created through literals, expressions that evaluate to a value.
All values are immutable—once created, they do not change. The number
3 is always the number 3. The string "frozen" can never have its
character array modified in place.
Booleans
A boolean value represents truth or falsehood. There are two boolean literals,
true and false. Their class is Bool.
Numbers
Like other scripting languages, Wren has a single numeric type: double-precision floating point. Number literals look like you expect coming from other languages:
:::dart
0
1234
-5678
3.14159
1.0
-12.34
Numbers are instances of the Num class.
Strings
A string is an array of bytes. Typically, they store characters encoded in UTF-8, but you can put any byte values in there, even zero or invalid UTF-8 sequences. (You might have some trouble printing the latter to your terminal, though.)
String literals are surrounded in double quotes:
:::dart
"hi there"
A handful of escape characters are supported:
:::dart
"\0" // The NUL byte: 0.
"\"" // A double quote character.
"\\" // A backslash.
"\a" // Alarm beep. (Who uses this?)
"\b" // Backspace.
"\f" // Formfeed.
"\n" // Newline.
"\r" // Carriage return.
"\t" // Tab.
"\v" // Vertical tab.
A \u followed by four hex digits can be used to specify a Unicode code point:
:::dart
System.print("\u0041\u0b83\u00DE") // "AஃÞ"
A \x followed by two hex digits specifies a single unencoded byte:
System.print("\x48\x69\x2e") // "Hi."
Strings are instances of class String.
Ranges
A range is a little object that represents a consecutive range of integers.
They don't have their own dedicated literal syntax. Instead, the number class
implements the .. and ... operators to create
them:
:::dart
3..8
This creates a range from three to eight, including eight itself. If you want a
half-inclusive range, use ...:
:::dart
4...6
This creates a range from four to six not including six itself. Ranges are commonly used for iterating over a sequences of numbers, but are useful in other places too. You can pass them to a list's subscript operator to return a subset of the list, for example:
:::dart
var list = ["a", "b", "c", "d", "e"]
var slice = list[1..3]
System.print(slice) // ["b", "c", "d"]
Their class is Range.
Null
Wren has a special value null, which is the only instance of the class
Null. (Note the difference in case.) It functions a bit like
void in some languages: it indicates the absence of a value. If you call a
method that doesn't return anything and get its returned value, you get null
back.