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78 lines
2.6 KiB
Plaintext
78 lines
2.6 KiB
Plaintext
Variables and functions
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--Variables--
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MSE script has the notion of ''variables''.
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A variable is a name holding a value, assigned using the @:=@ operator:
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> variable := 1 + 1
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From now on (until another value is assigned) @variable@ evaluates to @2@ in the rest of the script.
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--Functions--
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It is possible to define your own [[type:function]]s in MSE script.
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The syntax for this is very simple, code in curly braces defines a function:
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> { code goes here }
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To be able to refer to the function it is usually assigned to a variable:
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> function := { code goes here }
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Calling a function is done using parentheses:
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> { code }()
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> function()
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this has the effect of evaluating the code inside the curly braces.
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--Scope--
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Assignments to variables are ''local'' to the current function.
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Consider:
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> function := {
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> x := "something else"
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> # here x is something else
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> }
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> x := 1
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> function()
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> # here x is still 1
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Unlike most programming languages MSE script uses [[http://en.wikipedia.org/wiki/Dynamic_scoping#Dynamic_scoping|dynamic scoping]].
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This means that assignments done in the calling function are visible in the called function:
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> fun := { "xyz is {xyz}" }
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> one := {
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> xyz := 1
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> fun()
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> }
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> two := {
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> xyz := "two"
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> fun()
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> }
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> one() == "xyz is 1"
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> two() == "xyz is two"
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--Parameters--
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The scoping can be used to pass parameters to functions as shown above.
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To make this easier, parameters can be specified inside the parentheses of the function call:
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> fun(xyz: "a parameter") == "xyz is a parameter"
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These assignments are ''only'' visible to the called function.
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> xyz := "outside"
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> fun(xyz: "a parameter")
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> # xyz is still "outside"
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The syntax for parameters is @name: value@.
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Multiple parameters are separated by commas.
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The special syntax @value@ (without a name) means the variable @input@ is used:
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> fun := { input + var2 }
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> fun(var2: "yes", "no") == "noyes"
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--Overriding functions--
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Like custom functions, the [[fun:index|built in functions]] are also stored in variables.
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It is possible to overwrite them:
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> to_upper := { input }
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> to_upper("xyz") == "xyz" # Not what it used to do
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A neat trick is adding 'extra' behaviour to functions.
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This can be done by first making a copy, and calling that:
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> real_to_upper := to_upper
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> to_upper := { "upper case: " + real_to_upper() }
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> to_upper("xyz") == "upper case: XYZ"
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Note that @real_to_upper@ is called without extra parameters, the @input@ variable is still set from the outer call to the new @to_upper@ itself.
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<div style="text-align:right;">next: <a href="control_structures">Control structures →</a></div>
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