Scala Reflection: How to list all variables in scope?

Question

How can I list the names and/or values of all "variables" (not just vars) in a scope/environment/binding?

To clarify, in the middle of a program/script or at some point in a REPL, I need to either (1) generate a list or (2) print a list of all entities that can be accessed by a Scala statement.

Answer 1

The question can be construed broadly, but for example the REPL has some support for javax.script with scoped bindings:

$ scala
Welcome to Scala version 2.11.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_11).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val e = $intp.asInstanceOf[javax.script.ScriptEngine]
e: javax.script.ScriptEngine = scala.tools.nsc.interpreter.ILoop$ILoopInterpreter@2b71fc7e

scala> e.getContext
res0: javax.script.ScriptContext = javax.script.SimpleScriptContext@63c12fb0

scala> e.getContext.getScopes
res1: java.util.List[Integer] = [100, 200]

scala> e.getContext.getBindings(100)
res2: javax.script.Bindings = {}

And the REPL itself keeps a scope that can be queried, representing the history of the current session that is automatically imported into the current line of script:

scala> $intp.replScope
res3: $intp.global.Scope = Scopes(value $intp, value e, value res0, value res1, value res2)

It's also possible to exercise REPL's completion mechanism:

scala> :power
** Power User mode enabled - BEEP WHIR GYVE **
** :phase has been set to 'typer'.          **
** scala.tools.nsc._ has been imported      **
** global._, definitions._ also imported    **
** Try  :help, :vals, power.<tab>           **

scala> reader.completion
res4: scala.tools.nsc.interpreter.Completion = scala.tools.nsc.interpreter.JLineCompletion@68b7bdcb

scala> res4.completer.complete("",0)
res6: scala.tools.nsc.interpreter.Completion.Candidates = Candidates(0,List($intp, $ires0, $ires1, $ires10, $ires11, $ires12, $ires13, $ires14, $ires15, $ires16, $ires17, $ires18, $ires2, $ires3, $ires4, $ires5, $ires6, $ires7, $ires8, $ires9, $r, AND, BLOCK, CASE, DEFAULT, FALSE, IF, LIT, NEW, NOT, NULL, REF, SOME, SelectStart, TRUE, TRY, UNIT, ZERO, analyzer, classOf, completion, e, fn, global, history, intp, isettings, lastRequest, mkTreeFromSelectStart, mkTreeMethods, mkTreeMethodsFromSelectStart, mkTreeMethodsFromSymbol, nullSafe, phased, power, r, reader, repl, replImplicits, res0, res1, res2, res3, res4, returning, scala$tools$nsc$ast$TreeDSL$CODE$$$outer, treedsl, typed, typer, vals))

scala> 

A single tab in the REPL console offers the autocomplete feature, which here shows all the junk in my current dir, which is on the class path by default:

$ scala
Welcome to Scala version 2.11.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_11).
Type in expressions to have them evaluated.
Type :help for more information.

scala> 
$intp          broken           enumtest       inheritthewind   maker           oracle        sbtbomb             thingy         
P              bumper           erased         inlined          mangled         orelse        scala               throwgen       
Q              butwhen          exh            inliner          mapeach         org           scallop             thrownull      
SO22581163     bytype           eyeshadow      inner            maqicode        othercase     scrap               tiles          
_root_         callbacks        fany           inputcheck       matchprim       out           scripts             timezone       
a              capture          featureless    intcake          maybeamb        overdone      searchme            tmp            
abjectfuture   cce              ff             interp           maykov          overnullary   selfpub             toString       
absval         cdtest           fielding       interpat         metamac         pathmaker     seqto               tops           
adaptation     charmatch        filloval       intpbind         mkarray         peasy         serialmigration     trial          
akka           choosy           filrdr         intupolated      mksym           pet           serious             tribool        
algedu         classOf          findwidgets    invokeFrom       modtest         petconfig     shapelessed         tricks         
angeldance     classmatch       finf           isInstanceOf     myanno          phyl          simple-swing        trivial        
annee          classy           fixedimp       isanon           mydays          pickit        singleton           tryxform       
annie          cmpprs           fixes          isfun            myintp          pimpin        slider              tstest         
annoconst      coltfred         fixme          isscala          mypkg           pkginvoke     slow                typeref        
annot          com              flib           java             mypriv          plugincp      smtest              tztest         
anymember      compilit         foodir         javafx           nestedmain      plugs         sobral              unapplynull    
anything       convprs          fooplus        javax            netscape        pointers      somatch             unavail        
applied        copier           for29          jbyte            newfrom         pointopt      some_package        unensured      
arrow          corner           formac         jdk              nextcompleted   pos           sortitout           unused         
asInstanceOf   counted          ftw            jex              niolock         poster        sounds              updater        
atrait         countints        funk           jext             noany           pow           specbug             valdef         
autoenum       cr               funkstr        jline            noapp           preferthunk   speck               vec            
auxctor        ctag             futfilter      jmap             nodep           prettycase    splitat             version        
bad-scales     curtest          futuremap      jover            nofeature       primover      stale               vowelshift     
badXlint       cyclic           fval           jperms           nofuture        printer       statik              w              
badaccess      dbadd            gline          junk             noimp           privctor      str2int             warnadapt      
badbob         default-tparam   global         k                noinline        privover      strtyp              weakerr        
badgeneric     delayed          goodbye        kcharex          nointerp        procked       structural-return   welper         
badimp         delayedsignal    gr             keptstar         nonl            protcase      stupid              whose          
badinherit     delineate        grapher        kmap             norec           protval       succinctly          widgets        
badmap         demoapi          groupby        lazyparadox      nosehorn        publicity     sun                 wrappedarray   
badmatch       dep              guiced         lazyside         nothingannot    q             superduper          wtf            
badover        doc              guy            lazysplit        ns              qqparms       sxema               x              
badoverride    dockable         halfinterval   lib              nts             quickly       syncd               xmladd         
badpath        dosth            here           liner            nullgroup       quoterep      syshook             xmlex          
badpkg         doublearrow      hidden         linetest         nullpair        rawj          t1                  xmlregex       
badseal        dummyonly        hiddenimport   linted           nulltype        raws          t1807               xmlreplace     
badstrimp      dynospec         id             linty            nummaker        reader        t5148               xmlsub         
badvargs       earlier          imparted       lit              off             reflectenum   t5589               xmlt           
badvol         eatery           imparter       littlecake       oiler5          replslow      t7121               xxx            
bigmethod      email            impctx         looker           old-and-blue    repro         t7775               zed            
binder         empty            impless        lookit           oldname         required      t8433                              
biterpolator   emptypackage     impmag         lookup           om              sample-foo    tabpane                            
blocking       enclosing        imptest        loopy            oneq            samplewarn    taggedparam                        
blownfuture    enclosingcls     imptrait       macinfer         oops            saver         target                             
bounded        enpatch          include        macvar           optdate         sbt-test      teachers                           

scala>