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310 lines
8.9 KiB
Markdown
310 lines
8.9 KiB
Markdown
{
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target: "reference/command_line"
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template: "reference"
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title: "Command Line Tools"
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short_name: "command_line"
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}
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# Command Line Tools
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Two tools are installed with MoonScript, `moon` and `moonc`.
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`moonc` is for compiling MoonScript code to Lua.
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`moon` is for running MoonScript code directly.
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## `moon`
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`moon` can be used to run MoonScript files directly from the command line,
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without needing a separate compile step. All MoonScript files are compiled in
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memory as they are executed.
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```bash
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$ moon my_script.moon
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```
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Any MoonScript files that are required will also be compiled on demand as they
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are loaded.
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When an error occurs during runtime, the stack trace is rewritten to give line
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numbers from the original `.moon` file.
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If you want to disable [error rewriting](#error_rewriting), you can pass the
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`-d` flag. A full list of flags can be seen by passing the `-h` or `--help`
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flag.
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### Error Rewriting
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Runtime errors are given special attention when running code using the `moon`
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command line tool. Because code is written in MoonScript but executed as Lua,
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errors that happen during runtime report Lua line numbers. This can make
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debugging less than ideal.
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In order to solve this problem MoonScript builds up a table of line number
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mappings, allowing the runtime to calculate what line of MoonScript generated
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the line of Lua that triggered the error.
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Consider the following file with a bug (note the invalid `z` variable):
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```moon
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add_numbers = (x,y) -> x + z -- 1
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print add_numbers 10,0 -- 2
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```
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The following error is generated:
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moon: scrap.moon:1(3): attempt to perform arithmetic on global 'z' (a nil value)
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stack traceback:
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scrap.moon:1(3): in function 'add_numbers'
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scrap.moon:2(5): in main chunk
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Notice how next to the file name there are two numbers. The first number is the
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rewritten line number. The number in the parentheses is the original Lua line
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number.
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The error in this example is being reported on line 1 of the `moon` file, which
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corresponds to line 3 of the generated Lua code. The entire stack trace is rewritten in
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addition to the error message.
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### Code Coverage
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`moon` lets you run a MoonScript file while keeping track of which lines
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are executed with the `-c` flag.
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For example, consider the following `.moon` file:
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```moononly
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-- test.moon
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first = ->
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print "hello"
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second = ->
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print "world"
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first!
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```
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We can execute and get a glance of which lines ran:
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```bash
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$ moon -c test.moon
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```
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The following output is produced:
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------| @cool.moon
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1| -- test.moon
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* 2| first = ->
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* 3| print "hello"
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4|
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* 5| second = ->
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6| print "world"
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7|
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* 8| first!
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9|
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The star next to the line means that it was executed. Blank lines are not
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considered when running so by default they don't get marked as executed.
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## `moonc`
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`moonc` is used for transforming MoonScript files into Lua files.
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It takes a list of files, compiles them all, and creates the associated `.lua`
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files in the same directories.
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```bash
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$ moonc my_script1.moon my_script2.moon ...
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```
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You can control where the compiled files are put using the `-t` flag, followed
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by a directory.
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`moonc` can also take a directory as an argument, and it will recursively scan
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for all MoonScript files and compile them.
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`moonc` can write to standard out by passing the `-p` flag.
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The `-w` flag can be used to enable watch mode. `moonc` will stay running, and
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watch for changes to the input files. If any of them change then they will be
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compiled automatically.
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A full list of flags can be seen by passing the `-h` or `--help` flag.
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### Syntax Transformer
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A syntax transformer is a function that manipulates MoonScript code before
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compiling to Lua. It operates on the parsed AST (Abstract Syntax Tree). It can
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be used to implement macros, change syntax, optimize code, among other things.
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You specify the name of a Lua module. This module must return a single function
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(or callable object) that takes AST as an argument, and returns the new AST.
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```bash
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moonc --transform my_transfomer my_script.moon
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```
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The transform can fail by returning `nil` and an error message. MoonScript AST
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is currently undocumented, so you'll have to experiment by printing out the AST
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to see how to make changes. MoonScript AST is made up of standard Lua tables
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that are nested.
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### Linter
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`moonc` contains a [lint][1] tool for statically detecting potential problems
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with code. The linter has two tests: detects accessed global variables,
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detect unused declared variables. If the linter detects any issues with a file,
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the program will exit with a status of `1`.
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You can execute the linter with the `-l` flag. When the linting flag is
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provided only linting takes place and no compiled code is generated.
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The linter is compatible with the watch mode (see above) for automatic linting.
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```bash
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moonc -l file1.moon file2.moon
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```
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Like when compiling, you can also pass a directory as a command line argument
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to recursively process all the `.moon` files.
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#### Global Variable Checking
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It's considered good practice to avoid using global variables and create local
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variables for all the values referenced. A good case for not using global
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variables is that you can analyize the code ahead of time without the need to
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execute it to find references to undeclared variables.
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MoonScript makes it difficult to declare global variables by forcing you to be
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explicit with the `export` keyword, so it's a good candidate for doing this
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kind of linting.
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Consider the following program with a typo: (`my_number` is spelled wrong as
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`my_nmuber` in the function)
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```moononly
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-- lint_example.moon
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my_number = 1234
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some_function = ->
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-- a contrived example with a small chance to pass
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if math.random() < 0.01
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my_nmuber + 10
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some_function!
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```
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Although there is a bug in this code, it rarely happens during execution. It's
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more likely to be missed during development and cause problems in the future.
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Running the linter immediately identifies the problem:
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```bash
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$ moonc -l lint_example.moon
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```
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Outputs:
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./lint_example.moon
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line 7: accessing global `my_nmuber`
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==================================
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> my_nmuber + 10
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#### Global Variable Whitelist
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In most circumstances it's impossible to avoid using some global variables. For
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example, to access any of the built in modules or functions you typically
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access them globally.
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For this reason a global variable whitelist is used. It's a list of global
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variables that are allowed to be used. A default whitelist is provided that
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contains all of Lua's built in functions and modules.
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You can create your own entires in the whitelist as well. For example, the
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testing framework [Busted](http://olivinelabs.com/busted) uses a collection of
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global functions (like `describe`, `before_each`, `setup`) to make writing
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tests easy.
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It would be nice if we could allow all of those global functions to be called
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for `.moon` files located in the `spec/` directory. We can do that by creating
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a `lint_config` file.
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`lint_config` is a regular MoonScript or Lua file that provides configuration
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for the linter. One of those settings is `whitelist_globals`.
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To create a configuration for Busted we might do something like this:
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```moononly
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-- lint_config.moon
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{
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whitelist_globals: {
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["spec/"]: {
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"it", "describe", "setup", "teardown",
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"before_each", "after_each", "pending"
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}
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}
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}
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```
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Compile the file:
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```bash
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$ moonc lint_config.moon
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```
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Then run the linter on your entire project:
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```bash
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$ moonc -l .
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```
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The whitelisted global references in `spec/` will no longer raise notices.
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The `whitelist_globals` property of the `lint_config` is a table where the keys
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are Lua patterns that match file names, and the values are an array of globals
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that are allowed.
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Multiple patterns in `whitelist_globals` can match a single file, the union of
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the allowed globals will be used when linting that file.
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#### Unused Variable Assigns
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Sometimes when debugging, refactoring, or just developing, you might leave
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behind stray assignments that aren't actually necessary for the execution of
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your code. It's good practice to clean them up to avoid any potential confusion
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they might cause.
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The unused assignment detector keeps track of any variables that are assigned,
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and if they aren't accessed in within their available scope, they are reported
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as an error.
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Given the following code:
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```moononly
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a, b = 1, 2
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print "hello", a
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```
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The linter will identify the problem:
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./lint_example.moon
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line 1: assigned but unused `b`
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===============================
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> a, b = 1, 2
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Sometimes you need a name to assign to even though you know it will never be
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accessed. The linter will treat `_` as a special name that's allowed to be
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written to but never accessed:
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The following code would not produce any lint errors:
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```moononly
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item = {123, "shoe", "brown", 123}
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_, name, _, count = unpack item
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print name, count
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```
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[1]: http://en.wikipedia.org/wiki/Lint_(software)
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