String to commands

BlitzMax Forums/BlitzMax Programming/String to commands

Heliotrope

(Posted 2015) [#1]

Hi all, in Blitz is there a way to convert user inputed strings to commands? So that rather than typing

if string_in = stringcommand1 then command1
if string_in = stringcommand2 then command2
...

you can type

for a$ = eachin list_of_accepted_commands
if a$ = string_in then run string_in
next

so that after checking to see if it is valid the program will literally run the string.

xlsior

(Posted 2015) [#2]

No -- since Blitz code gets converted to machine language at compile time, the blitz commands cease to exist at that point.

If you want to run code, you'll probably have to work with a scripting language like LUA
(there's several LUA modules available for BlitzMax)

Yasha

(Posted 2015) [#3]

For simple cases you can do something like this:

Type Command Abstract
    Method Run:Object(args:Object[]) Abstract
End Type

Type Command1 Extends Command
    Method Run:Object(args:Object[])
        Print "we're in command 1"
    End Method
End Type

Type Command2 Extends Command
    Method Run:Object(args:Object[])
        Print "doing something else"
        Return args[2].ToString()
    End Method
End Type

Local commandMap:TMap = CreateMap()

For Local c:String = EachIn ["Command1", "Command2"]
    commandMap.Insert(c, TTypeId.ForName(c).NewObject())
Next

'...

Local cmd:String = Input(...etc
Local arg0:String = Input(...etc

Local result:Object = Command(commandMap.ValueForKey(cmd)).Run([arg0])

You can extend this idea with e.g. metadata declarations to easily and automatically verify the size of the argument arrays.

This will handle basic commands with simple arguments (no variable substitution). For something more complicated, like loops or custom function definitions, as xlsior says, a full scripting language is what you need.