Function return value declarations that cause compiler errors (and an effective workaround) in AGK Studio tier 1

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GemGames

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Location: Edmonton, Alberta, Canada

Posted: 22nd Jan 2024 02:28

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A compiler error occurs in AppGameKit Studio tier 1 if a function is defined using both a parameter list and a declared return type.

+ Code Snippet

function TestReturnValue(parameter1 as integer) as integer
  Print("This is a test function, and it is designed to return the value of 123.")
  Sync()
endfunction 123

The compiler will report: 'Error: Unexpected token "as", function declaration must end with a new line'

However, if the same function is defined with a parameter list but without a declared return type, it will compile.

+ Code Snippet

function TestReturnValue(parameter1 as integer)
  Print("This is a test function, and it is designed to return the value of 123.")
  Sync()
endfunction 123

Similarly, if the same function is defined without any parameter list, but with a declared return type, then it will compile.

+ Code Snippet

function TestReturnValue() as integer
  Print("This is a test function, and it is designed to return the value of 123.")
  Sync()
endfunction 123

Notice that the function syntax which triggers a compiler error has both a parameter list and a declared return type. To my knowledge, this is (should be) acceptable syntax. I am not sure if this is a bug in the compiler, or if this detection is intentional.

In any case, an effective workaround is to define the function without a declaration of a return type, even if the function does return a value. This is an imperfect solution, but it seems to work effectively.

Does anyone else have any suggestions or recommendations for a better solution than the workaround I listed? Is it incorrect syntax to have a function which has both a parameter list and a declared return type? Thanks in advance for any suggestions or insights.

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blink0k

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Posted: 22nd Jan 2024 05:20

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This post has been marked by the post author as the answer.

The function statement does not have an "as" clause

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GemGames

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Posted: 23rd Jan 2024 02:24

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Thanks, I suppose I am mixing up dialects of BASIC with AppGameKit tier 1. In VBA for example, it is entirely legal to make the following statement as the 1st line in a function definition:

+ Code Snippet

function MyCustomFunction (parameterName as double) as double

This line defines the function name, its parameters, and its return type (if any). The above code snippet will generate a compiler error in AGK.

It seems strange to me however, that the following code snippet without parameters is legal syntax in AGK...

+ Code Snippet

function MyCustomFunction() as float

...while this following code snippet is illegal syntax in AppGameKit, with the addition of parameters:

+ Code Snippet

function MyOtherCustomFunction(parameterName as integer) as integer

This seems inconsistent to me within AGK. But, as long as the "as integer" phrase is omitted, it works well enough in AGK. I suppose this is primarily a matter of semantics amongst some different dialects of BASIC. Programming in one dialect tends to establish programming habits which carry over to other dialects which require different syntax.

Thank you for your valuable input in the previous post, I appreciate that!

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Kevin Picone

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Posted: 24th Jan 2024 03:48

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Not sure it's supported, it's most likely just ignored.

For example what does it think of a function that's exporting a float.

+ Code Snippet

  print TestReturnValue()

function TestReturnValue() as integer
  Print("This is a test function, and it is designed to return the value of 123.")
  Sync()
endfunction 123.456

+ Code Snippet


  print TestReturnValue()

function TestReturnValue() as integer
  Print("This is a test function, and it is designed to return the value of 123.")
  Sync()
endfunction "Hello World"

If it parses the 'as integer' it should notice that mismatch and spit and warning / error.. But I suspect it'll following their existing pattern and use the EndFunction expression to get the return type making the 'as integer' a oversight in the initial prototype.

PlayBASIC To HTML5/WEB - Convert PlayBASIC To Machine Code

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GemGames

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Posted: 24th Jan 2024 05:45 Edited at: 24th Jan 2024 06:25

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Quote: "If it parses the 'as integer' it should notice that mismatch and spit and warning / error.. But I suspect it'll following their existing pattern and use the EndFunction expression to get the return type making the 'as integer' a oversight in the initial prototype."

That's a good point. No mismatch is detected, and no warning or error is generated by the compiler, which leads me to believe that the "as integer" or "as float" is simply ignored by the compiler.

The compiler will issue an error however if a function's internally placed exitfunction's value is given which is of a different variable type than the same function's endfunction's value's type.
For example, the following function will generate a compiler error:

+ Code Snippet

function TestFunction()
     exitfunction 123
/*
     This is not allowed (and causes a compiler error) because the compiler is expecting the function to return a string type,
     based on the endfunction command's value's type (in this case, a string type).
*/
endfunction "The default return value is a string type." 
/*
     This line defines not only the function's default return value, but furthermore also by inference the function's return type.
     By making this inference from the endfunction command, it invalidates any integer type or
     float type return value following an exitfunction command inside the function.
*/

In contrast this function, with an identical body as the previous function, will not generate a compiler error:

+ Code Snippet

function TestFunction()
     exitfunction 123
/*
     exitfunction 123 is allowed because the compiler is expecting the function to return an integer type,
     based on the endfunction command's value type.
*/
endfunction 456
/*
     endfunction 456 defines both the default return value and by inference also the function's
     return type (an integer, because in this case 456 happens to be an integer).
*/

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GemGames

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Posted: 24th Jan 2024 06:03 Edited at: 24th Jan 2024 06:05

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Furthermore, if no return type is given by the endfunction keyword, then if an internal exitfunction command tries to return any value of any type, a compiler error results.

+ Code Snippet

function TestFunction()
     exitfunction 123
/*
     This is not allowed (and will generate a compiler error) because based on endfunction's nonexistent return value's type
     (no return value = return type "null") the compiler expects exitfunction to exit without any return value of any type.
     The compiler reports: 'Error: Unexpected token "", this function does not return a value'
*/
endfunction

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