GF shell: fix a parsing problem with the cc command

This patch fixes a problem introduced last year when the GF shell was
refactored to allow more commands to be treated uniformly and be part
of pipes. The cc command was one of those commands, but unfortunately this
introduced a parsing problem, e.g.

	> cc "last"
	constant not found: last

	> cc "last"++"year"
	command not parsed: cc "last"++"year"

This happened because the generic command line parser in
GF.Command.{Abstract,Parse} assumes that all commands have an argument of
type PGF.Expr. Commands that expect other types of arguments have to
use PGF.showExpr combined with other conversion to the argument type they
expect. The cc command excpets a GF.Grammar.Term, and unfortunately not 
all terms survice the roundtrip through PGF.Expr, in part because of
an additional hack to allow strings to be roundtripped through PGF.Expr
without adding superfluous double quotes.

To solve the problem, this patch

 + makes room for arguments of type Term in the Argument type in
   GF.Command.Abstract.
   
 + makes a special case for the cc command in GF.Command.Parse, by
   calling the partial parser 'runPartial pTerm' recently added in
   GF.Grammar.Lexer and GF.Grammar.Parser. Care was taken so that
   that "|" and ";" can be used both inside terms and as separators between
   commands in the shell, e.g. things like the following now work:

       > cc ("a"|"b") | ps -lexcode
       variants { "a" ; "b" }

 + introduces a type CommandArgument that replaces [Expr] as the
   type of values passed between commands in pipes. It has room for
   values of type [Expr], [String] and Term, thus eliminating the need
   to roundtrip through the Expr type all the time.
   The hack to avoid adding superfluous quotes when strings are
   roundtripped through Expr has been left in place for now,
   but can probably be removed.

src/compiler/GF/Command/Commands.hs

@@ -61,7 +61,8 @@ pgfCommands = Map.fromList [
        "by the view flag. The target format is png, unless overridden by the",
        "flag -format. Results from multiple trees are combined to pdf with convert (ImageMagick)."
        ],
-     exec = getEnv $ \ opts es (Env pgf mos) -> do
+     exec = getEnv $ \ opts arg (Env pgf mos) -> do
+         let es = toExprs arg
          let langs = optLangs pgf opts
          if isOpt "giza" opts
            then do
@@ -182,11 +183,11 @@ pgfCommands = Map.fromList [
        ("depth","the maximum generation depth"),
        ("probs", "file with biased probabilities (format 'f 0.4' one by line)")
        ],
-     exec = getEnv $ \ opts xs (Env pgf mos) -> do
+     exec = getEnv $ \ opts arg (Env pgf mos) -> do
        pgf <- optProbs opts (optRestricted opts pgf)
        gen <- newStdGen
        let dp = valIntOpts "depth" 4 opts
-       let ts  = case mexp xs of
+       let ts  = case mexp (toExprs arg) of
                    Just ex -> generateRandomFromDepth gen pgf ex (Just dp)
                    Nothing -> generateRandomDepth     gen pgf (optType pgf opts) (Just dp)
        returnFromExprs $ take (optNum opts) ts
@@ -212,10 +213,10 @@ pgfCommands = Map.fromList [
        mkEx "gt -cat=NP -depth=2    -- trees in the category NP to depth 2",
        mkEx "gt (AdjCN ? (UseN ?))  -- trees of form (AdjCN ? (UseN ?))"
        ],
-     exec = getEnv $ \ opts xs (Env pgf mos) -> do
+     exec = getEnv $ \ opts arg (Env pgf mos) -> do
        let pgfr = optRestricted opts pgf
        let dp = valIntOpts "depth" 4 opts
-       let ts = case mexp xs of
+       let ts = case mexp (toExprs arg) of
                   Just ex -> generateFromDepth pgfr ex (Just dp)
                   Nothing -> generateAllDepth pgfr (optType pgf opts) (Just dp)
        returnFromExprs $ take (optNumInf opts) ts
@@ -266,7 +267,7 @@ pgfCommands = Map.fromList [
        mkEx "gr -lang=LangHin -cat=Cl | l -table -to_devanagari -- hindi table",
        mkEx "l -unlexer=\"LangAra=to_arabic LangHin=to_devanagari\" -- different unlexers"
        ],
-     exec = getEnv $ \ opts ts (Env pgf mos) -> return . fromStrings $ optLins pgf opts ts,
+     exec = getEnv $ \ opts ts (Env pgf mos) -> return . fromStrings . optLins pgf opts $ toExprs ts,
      options = [
        ("all",    "show all forms and variants, one by line (cf. l -list)"),
        ("bracket","show tree structure with brackets and paths to nodes"),
@@ -291,7 +292,7 @@ pgfCommands = Map.fromList [
      examples = [
        mkEx "l -lang=LangSwe,LangNor -chunks ? a b (? c d)"
        ],
-     exec = getEnv $ \ opts ts (Env pgf mos) -> return . fromStrings $ optLins pgf (opts ++ [OOpt "chunks"]) ts,
+     exec = getEnv $ \ opts ts (Env pgf mos) -> return . fromStrings $ optLins pgf (opts ++ [OOpt "chunks"]) (toExprs ts),
      options = [
        ("treebank","show the tree and tag linearizations with language names")
        ] ++ stringOpOptions,
@@ -332,11 +333,11 @@ pgfCommands = Map.fromList [
      longname = "morpho_quiz",
      synopsis = "start a morphology quiz",
      syntax   = "mq (-cat=CAT)? (-probs=FILE)? TREE?",
-     exec = getEnv $ \ opts xs (Env pgf mos) -> do
+     exec = getEnv $ \ opts arg (Env pgf mos) -> do
          let lang = optLang pgf opts
          let typ  = optType pgf opts
          pgf <- optProbs opts pgf
-         let mt = mexp xs
+         let mt = mexp (toExprs arg)
          restricted $ morphologyQuiz mt pgf lang typ
          return void,
      flags = [
@@ -427,8 +428,8 @@ pgfCommands = Map.fromList [
        mkEx "pt -compute (plus one two)                               -- compute value",
        mkEx "p \"4 dogs love 5 cats\" | pt -transfer=digits2numeral | l -- four...five..."
        ],
-     exec = getEnv $ \ opts ts (Env pgf mos) ->
-            returnFromExprs . takeOptNum opts $ treeOps pgf opts ts,
+     exec = getEnv $ \ opts arg (Env pgf mos) ->
+            returnFromExprs . takeOptNum opts . treeOps pgf opts $ toExprs arg,
      options = treeOpOptions undefined{-pgf-},
      flags = [("number","take at most this many trees")] ++ treeOpFlags undefined{-pgf-}
      }),
@@ -481,7 +482,8 @@ pgfCommands = Map.fromList [
        "by the file given by flag -probs=FILE, where each line has the form",
        "'function probability', e.g. 'youPol_Pron  0.01'."
        ],
-     exec = getEnv $ \ opts ts (Env pgf mos) -> do
+     exec = getEnv $ \ opts arg (Env pgf mos) -> do
+         let ts = toExprs arg
          pgf <- optProbs opts pgf
          let tds = rankTreesByProbs pgf ts
          if isOpt "v" opts
@@ -503,11 +505,11 @@ pgfCommands = Map.fromList [
      longname = "translation_quiz",
      syntax   = "tq -from=LANG -to=LANG (-cat=CAT)? (-probs=FILE)? TREE?",
      synopsis = "start a translation quiz",
-     exec = getEnv $ \ opts xs (Env pgf mos) -> do
+     exec = getEnv $ \ opts arg (Env pgf mos) -> do
          let from = optLangFlag "from" pgf opts
          let to   = optLangFlag "to" pgf opts
          let typ  = optType pgf opts
-         let mt   = mexp xs
+         let mt   = mexp (toExprs arg)
          pgf <- optProbs opts pgf
          restricted $ translationQuiz mt pgf from to typ
          return void,
@@ -542,7 +544,8 @@ pgfCommands = Map.fromList [
        "flag -format. Results from multiple trees are combined to pdf with convert (ImageMagick).",
        "See also 'vp -showdep' for another visualization of dependencies." 
        ],
-     exec = getEnv $ \ opts es (Env pgf mos) -> do
+     exec = getEnv $ \ opts arg (Env pgf mos) -> do
+         let es = toExprs arg
          let debug = isOpt "v" opts
          let file = valStrOpts "file" "" opts
          let outp = valStrOpts "output" "dot" opts
@@ -552,7 +555,7 @@ pgfCommands = Map.fromList [
          let lang = optLang pgf opts
          let grphs = map (graphvizDependencyTree outp debug mlab Nothing pgf lang) es
          if isOpt "conll2latex" opts
-           then return $ fromString $ conlls2latexDoc $ stanzas $ unlines $ toStrings es
+           then return $ fromString $ conlls2latexDoc $ stanzas $ unlines $ toStrings arg
            else if isFlag "view" opts && valStrOpts "output" "" opts == "latex"
              then do
                let view = optViewGraph opts
@@ -596,7 +599,8 @@ pgfCommands = Map.fromList [
        "by the view flag. The target format is png, unless overridden by the",
        "flag -format. Results from multiple trees are combined to pdf with convert (ImageMagick)."
        ],
-     exec = getEnv $ \ opts es (Env pgf mos) -> do
+     exec = getEnv $ \ opts arg (Env pgf mos) -> do
+         let es = toExprs arg
          let lang = optLang pgf opts
          let gvOptions = GraphvizOptions {noLeaves = isOpt "noleaves" opts && not (isOpt "showleaves" opts),
                                           noFun = isOpt "nofun" opts || not (isOpt "showfun" opts),
@@ -661,7 +665,8 @@ pgfCommands = Map.fromList [
        "flag -format. Results from multiple trees are combined to pdf with convert (ImageMagick).",
        "With option -mk, use for showing library style function names of form 'mkC'."
        ],
-     exec = getEnv $ \ opts es (Env pgf mos) ->
+     exec = getEnv $ \ opts arg (Env pgf mos) ->
+      let es = toExprs arg in
        if isOpt "mk" opts
        then return $ fromString $ unlines $ map (tree2mk pgf) es
        else if isOpt "api" opts
@@ -707,7 +712,7 @@ pgfCommands = Map.fromList [
        "metavariables and the type of the expression."
        ],
      exec = getEnv $ \ opts arg (Env pgf mos) -> do
-       case arg of
+       case toExprs arg of
          [EFun id] -> case Map.lookup id (funs (abstract pgf)) of
                         Just fd -> do putStrLn $ render (ppFun id fd)
                                       let (_,_,_,prob) = fd
@@ -748,7 +753,10 @@ pgfCommands = Map.fromList [
 
    fromParse opts = foldr (joinPiped . fromParse1 opts) void
 
-   joinPiped (Piped (es1,ms1)) (Piped (es2,ms2)) = Piped (es1++es2,ms1+++-ms2)
+   joinPiped (Piped (es1,ms1)) (Piped (es2,ms2)) = Piped (jA es1 es2,ms1+++-ms2)
+     where
+       jA (Exprs es1) (Exprs es2) = Exprs (es1++es2)
+       -- ^ fromParse1 always output Exprs
 
    fromParse1 opts (s,(po,bs))
      | isOpt "bracket" opts = pipeMessage (showBracketedString bs)