Visual Basic-to-LiveCode cheat sheet
Programmers coming into LiveCode from Visual Basic or another Basic language may find the following helpful in figuring out the differences in environments.
In most cases a direct translation of VB to LiveCode is not the best way to code any given problem. As with any programming language, there are many ways to accomplish any task. Direct translation will provide the fastest way to get a project converted, but from there out a rethinking of the code will provide code that executes faster in fewer lines, is more readable and maintainable, and may offer new insights into how to solve a problem.
The following is a starting point for developers looking into converting an existing project or coming to grips with the differences.
Assignments
XTalk languages follow a natural-language approach. In general, statements are of the imperative form in which there is an implied second-person subject of the statement (you) and the verb is the first word of the line: "put value into container", "add 1 to someVariable", etc.
Thus the VB syntax in which some statements have an implied verb ("X=4" instead of "LET X=4") must be translated to LiveCode syntax "put 4 into x".
BASIC LiveCode
lblTemperature.Text = 98.6 put 98.6 into field "lblTemperature"
xyz = xyz + 1 add 1 to xyz
let x = 3.14 put 3.14 into x
Arrays
Arrays: Arrays in LiveCode are associative - the index may be, but does not need to be, numeric in order to access array elements. The VB array syntax arrayName(index) is replaced by arrayName[index]. There is no VB equivalent for a non-numeric array index.
BASIC LiveCode
arrayName(4) = "hello" put "hello" into arrayName[4]
put "hello" into arrayName["greeting"]
put "bonjour" into arrayName["greeting",tCurrentLanguage]
put "bonjour" into arrayName["greeting"][tCurrentLanguage]
put translationArray["hello"]["French"] into field "localizedGreeting"
User-defined types
While there are no user-defined types in LiveCode, their use can be simulated using arrays:
Private Type Node
Row As Integer --row of the actual node
Col As Integer --column of the actual node
ParentId As Integer --parent node
ScoreF As Integer --Score F (total cost)
ScoreG As Integer --Score G (Cost of the path done)
ScoreH As Integer --Score H (Estimated cost of the path to do)
Closed As Boolean --indicates if the node is in the close list
End Type
Node.Row = 34
Node.Col = 25
Node.Closed = False
becomes
local tNode
put 34 into tNode["Row"]
put 25 into tNode["Col"]
put false into tNode["Closed"]
You can't say
Dim CurrNode as Node
Dim TargetNode as Node
TargetNode["Row"] = 34
CurrentNode["Col"] = 25
but you can say
local tNodes
put 34 into tNodes["TargetNode"]["Row"]
put 25 into tNodes["CurrentNode"]["Col"]
-- pick from the array of arrays
put tNodes["TargetNode"]["Row"] into tRowValue
or
local tNode
put 34 into Node["Row"]
put Node into tNodes["TargetNode"]
-- get just the individual node array
put tNodes["TargetNode"] into tNode
put tNode["Row"] into tRowValue
Return values
The odd VB syntax of returning a value from a function (procedure) by assigning the value to the name of the procedure is replaced in LiveCode by the more standard return keyword.
SUB PROCNAME
PROCNAME = someValue 'return someValue
END SUB
Similarities
Similarities: LiveCode, like VB, is not case-specific: somevariable is the same as someVariable, as are SOMEVARIABLE and sOmEvArIAblE. Unless explicitVars is set to true (enable variable checking in the menu) variables do not need to be declared before use. This is similar to VB's OPTION EXPLICIT. In LiveCode, single-word string literals should be, but in general do not have to be (unless explicitVars is true), quoted:
put red into tCurrentColor
put "black" into tCurrentColor
answer hello
answer "hello, sailor"
The following are not necessary in LiveCode:
REDIM
LET
PI is already defined as a constant
Direct mapping from VB to LiveCode
The following VB constants map directly to the following LiveCode keywords:
BASIC LiveCode
vbCRLF cr or return
vbKeyReturn cr or return
vbNewLine cr
vbKeyBack 8
vbOKOnly "OK"
vbNullString empty
vbBlack "black"
vbWhite "white"
vbRed "red"
vbBlue "blue"
vbGreen "green"
vbYellow "yellow"
vbMagenta "magenta"
vbCyan "cyan"
more direct mapping:
BASIC LiveCode
' (comment indicator) "--" or "#" or "//"
DIM X AS INTEGER local x or global x
PROCEDURE SomeProc function SomeProc
DO repeat
WHILE repeat while
WEND end while
LOOP end while
SELECT CASE switch (use break statement between cases)
END SELECT end switch
CASE ELSE default
OPEN fileName as "x" open file fileName
CLOSE "x" close file fileName
OPTION EXPLICIT explicitVars
TRIM(SomeString) word 1 to -1 of SomeString
No mapping
The following VB keywords have no mapping:
ON ERROR (use try/catch construct)
The following constructs have no direct equivalent:
WITH
END WITH
label:
GOTO label
dot notation:
instead of "lblMyLabel.Height" use "the height of field "MyLabel"
Timer controls
possibly use invisible buttons with "send 'Timer' to me in (the interval of me) milliseconds"
System and ActiveX controls in external libraries
Screen coordinates
VB screen coordinates are in Twips rather than in pixels. There are usually 15 twips per pixel, although this can vary depending on display characteristics.
Switch statements
SELECT CASE/CASE/CASE ELSE/END SELECT constructs are represented by the switch construct in LiveCode. The biggest difference is that individual case statements need "break" statements to separate them (as in C or java) and to keep the code from falling through into the next case. In VB different case items that should execute the same code are placed on the same line; in LiveCode they are placed on separate lines.
BASIC LiveCode
SELECT CASE tValue switch tValue
CASE 1 case 1
routine1 routine1
break
CASE 2, CASE 3 case 2
case 3
routine2 routine2
break
CASE ELSE default
routine3 routine3
END SELECT end switch
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