Ancient Haskell version of jq. Might be useful someday. Maybe.

Parser.y

@@ -7,13 +7,21 @@ import Debug.Trace
 import Data.List
 import Control.Monad.Error
 import Control.Monad.Reader
+
+instance Error (Maybe a) where
+  noMsg = Nothing
+  strMsg = const Nothing
+
+instance (Error a, Error b) => Error (a, b) where
+  noMsg = (noMsg, noMsg)
+  strMsg s = (strMsg s, strMsg s)
 }
 
-%name runParser Exp
+%name runParser TopLevel
 %tokentype { Token }
 
 %monad { Either String }
-%error { \t -> fail $ "parse error: unexpected " ++ if null t then [] else (show $ head t) }
+%error { \t -> throwError $ "parse error: unexpected " ++ if null t then [] else (show $ t) }
 
 %token
   '|' { TRes "|" }
@@ -24,28 +32,61 @@ import Control.Monad.Reader
   '}' { TRes "}" }
   '(' { TRes "(" }
   ')' { TRes ")" }
+  '$' { TRes "$" }
+  'as' { TRes "as" }
   ',' { TRes "," }
   ':' { TRes ":" }
   '==' { TRes "==" }
+  '=' { TRes "=" }
   '+' { TRes "+" }
+  'def' { TRes "def" }
+  ';' { TRes ";" }
+  'else' { TRes "else" }
+  'and' { TRes "and" }
+  'or' { TRes "or" }
   Ident { TIdent $$ }
   String { TString $$ }
   Int { TInt $$ }
 
-%left '|'
+
+%left 'else'
+%right '|'
+%left '='
 %left ','
+%left 'and' 'or'
 %nonassoc '=='
 %left '+'
 
 %%
 
+TopLevel
+  : Defn TopLevel	{ withDefn $1 $2 }
+  | Exp			{ $1 }
+
 Exp 
-  : Exp '|' Exp         { $1 >| $3 }
+  : Exp 'else' Exp      { $1 `elsep` $3 }
+  | Assign '|' Exp	{ do { v <- snd $1; setvar (fst $1) v $3 } }
+  | Exp '|' Exp         { $1 >| $3 }
   | Exp ',' Exp         { $1 `mplus` $3 }
-  | Exp '==' Exp        { liftM2 eqj $1 $3 }
-  | Exp '+' Exp         { liftM2 plusj $1 $3 }
+  | Exp 'and' Exp	{ liftM2 andj $1 $3 }
+  | Exp 'or' Exp	{ liftM2 orj $1 $3 }
+  | Exp '=' Exp         { assignp $1 $3 }
+  | Exp '==' Exp        { liftM2 eqj (subexp $1) (subexp $3) }
+  | Exp '+' Exp         { liftM2 plusj (subexp $1) (subexp $3) }
   | Term                { $1 }
 
+Assign
+  : Term 'as' '$' Ident { ($4, $1) }
+
+Defn
+  : 'def' Ident '=' Exp ';' { ($2, [], $4) }
+  | 'def' Ident '(' ParamList ')' '=' Exp ';' { ($2, $4, $7) }
+
+ParamList
+  :			{ [] }
+  | Ident		{ [$1] }
+  | Ident ';' ParamList { $1:$3 }
+  
 ExpD
   : ExpD '|' ExpD       { $1 >| $3 }
   | ExpD '==' ExpD      { liftM2 eqj $1 $3 }
@@ -53,24 +94,26 @@ ExpD
 
 
 Term 
-  : '.'                 { ask }
+  : '.'                 { input }
   | Term '.' Ident      { $1 >| index $3 }
   | '.' Ident           { index $2 }
   | String              { constStr $1 }
-  | Term '[' Exp ']'    { do {t <- $1; i <- $3; lookupj t i} }
+  | Term '[' Exp ']'    { do {t <- $1; i <- subexp $3; lookupj t i} }
   | Term '[' ']'        { $1 >| childp }
   | '(' Exp ')'         { $2 }
   | '[' Exp ']'         { arrayp $2 }
+  | '[' ']' 		{ arrayp (callp "empty" []) }
   | Int                 { constInt $1 }
   | '{' MkDict '}'      { dictp $2 }
   | Ident '(' Exp ')'   { callp $1 [$3] }
   | Ident               { callp $1 [] }
+  | '$' Ident		{ getvar $2 }
 
 MkDict
   :                     { [] }
   | MkDictPair          { [$1] }
   | MkDictPair ',' MkDict { $1:$3 }
- 
+
 MkDictPair
   : Ident ':' ExpD      { (constStr $1, $3) }
   | Ident               { (constStr $1, index $1) }