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93 lines
2.2 KiB
Markdown
93 lines
2.2 KiB
Markdown
# MoonScript
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MoonScript compiles to Lua
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## Function Literals
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## Table Literals
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## Table Comprehensions
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## Conditionals
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## Import Statement
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Often you want to bring some values from a table into the current scope as
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local variables by their name. The import statement lets us accomplish this:
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import insert from table
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The multiple names can be given, each separated by a comma:
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import C, Ct, Cmt from lpeg
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Sometimes a function requires that the table be sent in as the first argument
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(when using the `:` syntax). As a shortcut, we can prefix the name with a `:`
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to bind it to that table:
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-- some object
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my_module =
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state: 100
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add: (value) =>
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self.state + value
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import :add from my_module
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print add(22) -- equivalent to calling my_module:get(22)
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## The Using Clause; Controlling Destructive Assignment
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While lexical scoping can be a great help in reducing the complexity of the
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code we write, things can get unwieldy as the code size increases. Consider
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the following snippet:
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i = 100
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-- many lines of code...
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my_func = ->
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i = 10
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while i > 0
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print i
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i -= 1
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my_func()
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print i -- will print 0
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In `my_func`, we've overwritten the value of `i` mistakenly. In this example it
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is quite obvious, but consider a large, or foreign code base where it isn't
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clear what names have already been declared.
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It would be helpful to say which variables from the enclosing scope we intend
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on change, in order to prevent us from changing others by accident.
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The `using` keyword lets us do that. `using nil` makes sure that no closed
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variables are overwritten in assignment. The `using` clause is placed after the
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argument list in a function, or in place of it if there are no arguments.
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i = 100
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my_func = (using nil) ->
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i = "hello" -- a new local variable is created here
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my_func()
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print i -- prints 100, i is unaffected
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Multiple names can be separated by commas. Closure values can still be
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accessed, they just cant be modified:
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tmp = 1213
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i, k = 100, 50
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my_func = (add using k,i) ->
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tmp = tmp + add -- a new local tmp is created
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i += tmp
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k += tmp
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my_func(22)
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print i,k -- these have been updated
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