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.
3.4 KiB
^title Syntax ^category language
Wren's syntax is designed to be familiar to people coming from C-like languages while being a bit simpler and more streamlined.
Scripts are stored in plain text files with a .wren file extension. Wren does
not compile ahead of time: programs are run directly from source, from top to
bottom like a typical scripting language. (Internally, programs are compiled to
bytecode for efficiency, but that's an implementation detail.)
Comments
Line comments start with // and end at the end of the line:
:::dart
// This is a comment.
Block comments start with /* and end with */. They can span multiple lines
or be within a single one. Unlike C, block comments can nest in Wren:
:::dart
/* This is /* a nested */ comment. */
Reserved words
Some people like to see all of the reserved words in a programming language in one lump. If you're one of those folks, here you go:
:::dart
break class construct else false for foreign if import
in is null return static super this true var while
Identifiers
Naming rules are similar to other programming languages. Identifiers start with a letter or underscore and may contain letters, digits, and underscores. Case is sensitive.
:::dart
hi
camelCase
PascalCase
_under_score
abc123
ALL_CAPS
Identifiers that start with underscore (_) are special in Wren. They are used
to indicate fields in classes.
Newlines
Newlines (\n) are meaningful in Wren. They are used to separate statements:
:::dart
// Two statements:
System.print("hi") // Newline.
System.print("bye")
Sometimes, though, a statement doesn't fit on a single line and jamming a newline in the middle would trip it up. To handle that, Wren has a very simple rule: It ignores a newline following any token that can't end a statement.
:::dart
System.print( // Newline here is ignored.
"hi")
In practice, this means you can put each statement on its own line and wrap them across lines as needed without too much trouble.
Blocks
Wren uses curly braces to define blocks. You can use a block anywhere a statement is allowed, like in control flow statements. Method and function bodies are also blocks. For example, here we have a block for the then case, and a single statement for the else:
:::dart
if (happy && knowIt) {
hands.clap
} else System.print("sad")
Blocks have two similar but not identical forms. Typically, blocks contain a series of statements like:
:::dart
{
System.print("one")
System.print("two")
System.print("three")
}
Blocks of this form when used for method and function bodies automatically
return null after the block has completed. If you want to return a different
value, you need an explicit return statement.
However, it's pretty common to have a method or function that just evaluates and returns the result of a single expression. For that, Wren has a more compact notation:
:::dart
{ "single expression" }
If there is no newline after the { (or after the parameter list in a
function), then the block may only contain a single
expression, and it automatically returns the result of it. It's exactly the
same as doing:
:::dart
{
return "single expression"
}