Code block

Quick reference

code-block = ’[’ ws [expression {wsr expression} ws] ‘]’

Code blocks are used to group together a series of expressions. They can be used on their own, as the body of methods, coroutines and closures, or sub-parts of some flow control expressions such as loop, if and case clauses, sync and race. For now let’s examine using code blocks on their own.

Like Smalltalk, SkookumScript uses square brackets [] to indicate the beginning and ending of a code block.

[expr1 expr2 expr3]

Simple whitespace (which includes comments) is used to separate / delimit between expressions—or even no whitespace if the separation is obvious to the compiler. Expressions do not need an end of expression / statement delimiter symbol (such as ;, . or newline)—the SkookumScript compiler knows what is and is not a valid expression, and figures it out for you.

Identical code blocks with different spacing

[expr1 expr2 expr3]

[
expr1
expr2
expr3
]

[expr1
 expr2
 expr3]
 
[
  expr1
    expr2
      expr3
        ]

Why use square brackets rather than curly braces {}, begin/end, etc.?

SkookumScript was initially inspired from Smalltalk which uses square brackets [] for code blocks so that is its heritage. There are many different ways to group expressions including do/end like Lua and indention (known as the off-side rule like Python, though using curly braces {} like C++, C# and JavaScript is probably the most widespread. C++ is the most common runtime/game engine language and the language that SkookumScript is written and embedded in so a common question is:

Why not use curly braces {} for code blocks?

It turns out that visual code differences can actually be an asset. It is common to switch back and forth from SkookumScript and the C++ used in a game engine. If the two languages have something that visually sets them apart at a glance, it makes it easier for coders’ brains to switch to “SkookumScript” mode or “C++” mode as needed. When the code gets too similar, coders start writing SkookumScript specific code in C++ files and C++ specific code in SkookumScript files. We’ve tried SkookumScript with both [] and {} and having the code look a little different with square brackets [] leads to less mistakes.

Also square brackets [] on many keyboards do not need the Shift key pressed to type them so they are clearly superior.

Code block result

The result of a code block is the result of the last expression in the series.

[
// Results not used
expr1
expr2
// Result used as result for whole code block
expr3 
]

So you can do some work with earlier expressions in a code block and then return a result at the end of the code block.

[
!result: do_something(get_some_info)
println("Here is the result: " result)
result // object/value returned by the code block 
]

Since the result of a code block is always the last expression, SkookumScript has no return command. Always ensure that the value you want to return from a code block is the last expression.

Code blocks to specify order

A code block allows several expressions to be used in the place of a single expression. Wherever a single expression can be used, a code block with several expressions can be used instead.

SkookumScript code is always evaluated in left to right order, with each expression grabbing as much text in a given set of script code as it can. This is particularly important to remember with operators since they have no precedence rules.

// Evaluated as 2 * (3 + 4) = 14
// not as (2 * 3) + 4 = 10
2 * 3 + 4

// Evaluated as test1? or (test2? and test3?)
test1? or test2? and test3?

However you can use code blocks and their square brackets [] to group expressions to specify a different order. Many other languages and standard mathematical notation achieves the same effect with parentheses / brackets ().

// Evaluated as (2 * 3) + 4 = 10
[2 * 3] + 4

// Evaluated as (test1? or test2?) and test3?
[test1? or test2?] and test3?

No special operator precedence order

Many languages have precedence rules for their operators such as multiplication * should be grouped together before addition +. However many languages have slight differences that can be a gotcha and source of errors and many programmers – even really experienced ones – cannot remember all the precedence rules correctly.

Due to this, it is generally considered to be good coding practice to explicitly specify the intended evaluation order using brackets () etc. even if a given expression evaluates in the order that you want due to precedence rules. Since SkookumScript has no precedence rules – similar to Smalltalk – specifying intended order other than simple left to right grouping is mandatory and you never need to worry if you are correctly remembering all the precedence order rules.