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String expression evaluation

lordosGouv

Hello,

I use the following functions to calculate the result of an expression that is saved in string format:

(lambda( (a b) evalstring( "a+2*b" ) ) 1 2)

is there any way to do the same thing when the parameters and their values are saved in lists whose length is not constant in runtime and variable names are saved as strings e.g.:

parameters = list("a" "b" "c" ...)

param_values = list(1 2 3 ...)

expression = "a+2*b+3*c+...."

Thank you in advance

Parents

  • Generally it's not the most efficient to do this kind of run-time evaluation, but if you can't avoid it (i.e. the expressions have to be in strings), you could could achieve it this way:

    procedure(CCFevalExprWithParameters(expr paramNames paramValues)
  eval(
    `let(,foreach(mapcar (name value) paramNames paramValues 
	list(concat(name) value))
      evalstring(expr)
    )
  )
)

    Then you'd use:

    CCFevalExprWithParameters(expression parameters param_values)

    The idea is that it builds a let statement with name-value pairs according to the lists you provided, and evaluates the string within that context.

    Regards,

    Andrew

  • in reply to Andrew Beckett

    In fact, here's a small improvement which means it only does a single evaluation - instead of an eval with an evalstring inside, it uses the SKILL parser (using linereadstring) to parse the expression, but only calls the evaluator once.

    procedure(CCFevalExprWithParameters(expr paramNames paramValues)
  eval(
    `let(,foreach(mapcar (name value) paramNames paramValues 
	list(concat(name) value))
      ,@linereadstring(evalstring(expr))
    )
  )
)

    Andrew

Reply
  • in reply to Andrew Beckett

    In fact, here's a small improvement which means it only does a single evaluation - instead of an eval with an evalstring inside, it uses the SKILL parser (using linereadstring) to parse the expression, but only calls the evaluator once.

    procedure(CCFevalExprWithParameters(expr paramNames paramValues)
  eval(
    `let(,foreach(mapcar (name value) paramNames paramValues 
	list(concat(name) value))
      ,@linereadstring(evalstring(expr))
    )
  )
)

    Andrew

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