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Nested foreach loop

T Opperman

In an attemt to make parametric simulation scripts a bit more readable, I wrote a macro that allows foreach loops to be nested. I have not tested it fully, but I would like the readers' input on my code. The code generates a string containing the foreach loop, before evaluating it. It feels a bit clumsy, but I was unable to think of an simpler way to do this. Any suggestions? 

TOForeachNestFunc=lambda( (Symbols Lists Commands)
let(((DeclareLoopVars nil) (DeclareLoopHead "") (DeclareLoopBody "") (DeclareLoopTail "")
	(MainLoop "foreach( (") (LetStringHead "let((") Result )
;We'll need to create a loop that declares the expanded sweep lists,
;before creating a main loop that runs through all the expanded sweep lists and
;executes the commands.

	foreach((List Symbol) Lists Symbols
	 DeclareLoopVars=cons(sprintf(nil "%sS" Symbol) DeclareLoopVars)
	 DeclareLoopBody=strcat(DeclareLoopBody sprintf(nil "%sS=cons(%s %sS) " Symbol Symbol Symbol))
	 DeclareLoopHead=strcat(DeclareLoopHead sprintf(nil "foreach(%s '%L " Symbol List ))
	 DeclareLoopTail=strcat(DeclareLoopTail ")")
	 MainLoop = strcat(MainLoop Symbol " ")
	)
	MainLoop = strcat(MainLoop ") ")

	foreach(Var reverse(DeclareLoopVars)
		LetStringHead=strcat(LetStringHead "(" Var " nil) ")
		MainLoop = strcat(MainLoop Var " ")
		)
	LetStringHead=strcat( LetStringHead ")")
	MainLoop = strcat(MainLoop "\n" Commands "\n) ")
	Result=strcat(LetStringHead "\n" DeclareLoopHead "\n" DeclareLoopBody "\n" DeclareLoopTail "\n" MainLoop "\n" ")")
	)
)



defmacro(TOForeachNest (Symbols Lists @rest Commands)
;Executes a nested foreach loop
;Symbols: A list of variables that are used in the commands.
;List:A list of lists that contain the values to be swept
;Example: 
;	TempL= '(-40.0 27.0 85.0)
;	VSupplyL= '(3.2 3.3 3.4)
;
;	TOForeachNest('(Temp VSupply) list(VSupplyL TempL)
;	printf("Temperature: %e, Supply Voltage: %e", Temp VSupply)
;	)
;expands to:
;	foreach(Temp TempL
;		foreach(VSupply VSupplyL
;			printf("Temperature: %e, Supply Voltage: %e\n", Temp VSupply)
;)
;)

	let((CommandString)
	CommandString=sprintf(nil "%L" ,Commands)
		CommandString=substring(CommandString 2 strlen(CommandString)-2)
		`let((Result)
			Result=funcall(,TOForeachNestFunc ,Symbols ,Lists ,CommandString)
			evalstring(Result)
		)
	)
)
Parents

  • Tjaart, Andrew,

    I couldn't resist coming up with a non-macro version for completeness (also at http://s.crosstwine.com/spb/8cda9957).

    I usually implement iteration constructs via higher-order functions, and sugar-coat them in a thin layer of macrology where/when it really improves readability.

    This one is a bit nasty because a function cannot know the number of nested loops at compile time; moreover, it reuses/mutates a single list of arguments across the whole iteration to mimimize consing.

    A "pure macro" implementation is arguably nicer in this case, even if less generic. Anyway, here you are:

    defun(MyMapnested1 (fn args argsTail lists)
  cond(
    (lists
     let( ((moreLists cdr(lists))
           (nextArgsTail cdr(argsTail)))
       foreach(item car(lists)
         rplaca(argsTail item)
         MyMapnested1(fn args nextArgsTail moreLists)
       )
     )
    )
    (t
     apply(fn args)
    )
  )
)

defun(MyMapnested (fn @rest lists)
  let( ((args mapcar(lambda( (_ignore) nil) lists)))
    MyMapnested1(fn args args lists)
  )
)

    Usage via higher-order functions:

    let( ((TempL '(-40 27 85))
      (VSupplyL '(3.2 3.3 3.4)))
  MyMapnested(
    lambda( (Temp VSupply)
      printf("Temperature: %L, Supply Voltage: %L\n" Temp VSupply)
    )
    TempL
    VSupplyL
  )
)

    And here is TOForeachNest implemented in terms of MyMapnested:

    defmacro(TOForeachNest (Symbols Lists @rest Commands)
  `MyMapnested(
     lambda( ,Symbols
       ,@Commands
     )
     ,@Lists
   )
)

    Cheers, -D

Reply

  • Tjaart, Andrew,

    I couldn't resist coming up with a non-macro version for completeness (also at http://s.crosstwine.com/spb/8cda9957).

    I usually implement iteration constructs via higher-order functions, and sugar-coat them in a thin layer of macrology where/when it really improves readability.

    This one is a bit nasty because a function cannot know the number of nested loops at compile time; moreover, it reuses/mutates a single list of arguments across the whole iteration to mimimize consing.

    A "pure macro" implementation is arguably nicer in this case, even if less generic. Anyway, here you are:

    defun(MyMapnested1 (fn args argsTail lists)
  cond(
    (lists
     let( ((moreLists cdr(lists))
           (nextArgsTail cdr(argsTail)))
       foreach(item car(lists)
         rplaca(argsTail item)
         MyMapnested1(fn args nextArgsTail moreLists)
       )
     )
    )
    (t
     apply(fn args)
    )
  )
)

defun(MyMapnested (fn @rest lists)
  let( ((args mapcar(lambda( (_ignore) nil) lists)))
    MyMapnested1(fn args args lists)
  )
)

    Usage via higher-order functions:

    let( ((TempL '(-40 27 85))
      (VSupplyL '(3.2 3.3 3.4)))
  MyMapnested(
    lambda( (Temp VSupply)
      printf("Temperature: %L, Supply Voltage: %L\n" Temp VSupply)
    )
    TempL
    VSupplyL
  )
)

    And here is TOForeachNest implemented in terms of MyMapnested:

    defmacro(TOForeachNest (Symbols Lists @rest Commands)
  `MyMapnested(
     lambda( ,Symbols
       ,@Commands
     )
     ,@Lists
   )
)

    Cheers, -D

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