109 lines
2.0 KiB
Markdown
109 lines
2.0 KiB
Markdown
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# Variables and Constants
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Misti uses `var` for variables and `val` for constant reference variables.
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Variables and constants must always be initialized.
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```misti
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// A variable, its value can be modified
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var accumulator = 0
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accumulator += 1
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```
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```misti
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// A "constant", its value cannot be modified
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val name = "Bob"
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// Illegal, will raise an error in compile time
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name = "Mike"
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```
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```md-info
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If a constant's value is a primitive value, it cannot be changed.
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<br />
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However, if it is a reference value, its inner attributes can still
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be changed, but not the reference itself.
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```
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## Identifiers
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Identifiers start with a lower case letter or underscore,
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and then can contain letters, numbers and underscores.
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They can not start with a dollar sign.
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```misti
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variable
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_variable
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var1
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v4r
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```
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If an identifier starts with an upper case letter, it is considered to be
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a Datatype.
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```misti
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Str
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Num
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Bool
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Array
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Map
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CustomDatatype
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```
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## Type inference
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Variable declarations have type inference.
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```misti
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val anInteger = 40
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val aFloat = 10.20e+4
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var aBoolean = true
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```
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The datatype can be optionally specified by placing it before `var` or `val`.
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```misti
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Int val anInteger = 40
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Float val aFloat = 10.20e+4
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Bool var aBoolean = true
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```
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However, if the variable is a constant created with `val`,
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this keyword is optional.
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So, the following are equivalent.
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```misti
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Str val name = "Juan"
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// is equivalent to
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Str name = "Juan"
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```
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It is not possible to omit `var`. So the following will not mean the same.
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```misti
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Str var age = 20
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// is not equivalent to
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Str age = 20
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// the previous statement is equivalent to:
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// Str val age = 20
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```
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The second statement will declare a constant, not a variable.
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## Assign a block to a variable
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Assigning a block to a variable will execute the block,
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and the last expression will be the value of the variable.
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```misti
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val roi =
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val income = someIncomeCalculation()
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val investment = 25000
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income / investment // This will be the value of `roi`
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```
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