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.
71 lines
1.9 KiB
Markdown
71 lines
1.9 KiB
Markdown
^title Variables
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^category language
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Variables are named slots for storing values. You can define a new variable in
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Wren using a `var` statement, like so:
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:::dart
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var a = 1 + 2
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This creates a new variable `a` in the current scope and initializes it with
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the result of the expression following the `=`. Once a variable has been
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defined, it can be accessed by name as you would expect.
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:::dart
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var animal = "Slow Loris"
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System.print(animal) // Prints "Slow Loris".
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## Scope
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Wren has true block scope: a variable exists from the point where it is defined
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until the end of the [block](syntax.html#blocks) where that definition appears.
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:::dart
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{
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System.print(a) // ERROR! a doesn't exist yet.
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var a = 123
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System.print(a) // "123"
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}
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System.print(a) // ERROR! a doesn't exist anymore.
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Variables defined at the top level of a script are *top-level* and are visible
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to the [module](modules.html) system. All other variables are *local*.
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Declaring a variable in an inner scope with the same name as an outer one is
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called *shadowing* and is not an error (although it's not something you likely
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intend to do much).
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:::dart
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var a = "outer"
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{
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var a = "inner"
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System.print(a) // Prints "inner".
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}
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System.print(a) // Prints "outer".
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Declaring a variable with the same name in the *same* scope *is* an error.
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:::dart
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var a = "hi"
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var a = "again" // ERROR!
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## Assignment
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After a variable has been declared, you can assign to it using `=`:
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:::dart
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var a = 123
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a = 234
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An assignment walks up the scope stack to find where the named variable is
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declared. It's an error to assign to a variable that isn't defined. Wren
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doesn't roll with implicit variable definition.
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When used in a larger expression, an assignment expression evaluates to the
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assigned value.
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:::dart
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var a = "before"
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System.print(a = "after") // Prints "after".
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**TODO: Top-level names.**
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