How to compile/eval a Scala expression at runtime? -

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new scala , looking pointers idiomatic solution, if there one.

i'd have arbitrary user-supplied scala functions (which allowed reference functions/classes have defined in code) applied data.

for example: have foo(s: string): string , bar(s: string): string functions defined in myprog.scala. user runs program this:

$ scala myprog data.txt --func='(s: str) => foo(bar(s)).reverse'

this run line line through data file , emit result of applying user-specified function line.

for points, can ensure there no side-effects in user-defined function? if not, can restrict function use only restricted subset of functions (which can assure safe)?

@kenjiyoshida has nice gist shows how eval scala code. note when using eval gist, not specifying return value result in runtime failure when scala defaults inferring nothing.

scala> eval("println(\"hello\")") hello java.lang.classcastexception: scala.runtime.boxedunit cannot cast scala.runtime.nothing$   ... 42 elided

vs

scala> eval[unit]("println(\"hello\")") hello

it nicely handles whatever's in scope well.

 object thing {    val thing: int = 5  }   object eval {     def apply[a](string: string): = {      val toolbox = currentmirror.mktoolbox()      val tree = toolbox.parse(string)      toolbox.eval(tree).asinstanceof[a]    }     def fromfile[a](file: file): =      apply(scala.io.source.fromfile(file).mkstring(""))     def fromfilename[a](file: string): =      fromfile(new file(file))   }   object thing2 {    val thing2 = eval[int]("thing.thing") // 5  }

twitter's util package used have util-eval, seems have been deprecated (and triggers compiler bug when compiled).

as second part of question, answer seems no. if disable default predef , imports yourself, user can functions qualified package name. perhaps use scala's scala.tools.reflect.toolbox first parse string , compare against whitelist, before passing eval, @ point things pretty hairy since you'll manually writing code sanitize scala ast (or @ least reject dangerous input). doesn't seem "idiomatic solution."


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