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+%% Note: this SDF grammar is no longer used in the Nix expression
+%% parser and may not be up to date.
+
+definition
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% Top level syntax.
+
+module Main
+imports Nix-Exprs Nix-Layout
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% Expressions.
+
+module Nix-Exprs
+imports Nix-Lexicals
+exports
+  sorts Expr Formal Bind ExprList
+  context-free start-symbols Expr
+  context-free syntax
+
+    Id -> Expr {cons("Var")}
+    Int -> Expr {cons("Int")}
+    Str -> Expr {cons("Str")}
+    Uri -> Expr {cons("Uri")}
+    Path -> Expr {cons("Path")}
+
+    "(" Expr ")" -> Expr {bracket}
+
+    Expr Expr -> Expr {cons("Call"), left}
+
+    Id ":" Expr -> Expr {cons("Function1")}
+    "{" {Formal ","}* "}" ":" Expr -> Expr {cons("Function")}
+    Id -> Formal {cons("NoDefFormal")}
+    Id "?" Expr -> Formal {cons("DefFormal")}
+
+    "assert" Expr ";" Expr -> Expr {cons("Assert")}
+
+    "with" Expr ";" Expr -> Expr {cons("With")}
+
+    "rec" "{" Bind* "}" -> Expr {cons("Rec")}
+    "let" Bind* "in" Expr -> Expr {cons("Let")}
+    "let" "{" Bind* "}" -> Expr {cons("LetRec")}
+    "{" Bind* "}" -> Expr {cons("Attrs")}
+
+    Id "=" Expr ";" -> Bind {cons("Bind")}
+    "inherit" ("(" Expr ")")? Id* ";" -> Bind {cons("Inherit")}
+
+    "[" ExprList "]" -> Expr {cons("List")}
+    -> ExprList {cons("ExprNil")}
+    Expr ExprList -> ExprList {cons("ExprCons")}
+
+    Expr "." Id -> Expr {cons("Select")}
+
+    "if" Expr "then" Expr "else" Expr -> Expr {cons("If")}
+
+    Expr "==" Expr -> Expr {cons("OpEq"), non-assoc}
+    Expr "!=" Expr -> Expr {cons("OpNEq"), non-assoc}
+
+    "!" Expr -> Expr {cons("OpNot")}
+    Expr "&&" Expr -> Expr {cons("OpAnd"), right}
+    Expr "||" Expr -> Expr {cons("OpOr"), right}
+    Expr "->" Expr -> Expr {cons("OpImpl"), right}
+
+    Expr "//" Expr -> Expr {cons("OpUpdate"), right}
+    Expr "~" Expr -> Expr {cons("SubPath"), non-assoc}
+    Expr "?" Id -> Expr {cons("OpHasAttr")}
+    Expr "+" Expr -> Expr {cons("OpPlus"), left}
+    Expr "++" Expr -> Expr {cons("OpConcat"), right}
+
+  context-free priorities
+
+    Expr "." Id -> Expr
+  > Expr ExprList -> ExprList
+  > Expr Expr -> Expr
+  > Expr "~" Expr -> Expr
+  > Expr "?" Id -> Expr
+  > Expr "++" Expr -> Expr
+  > Expr "+" Expr -> Expr
+  > "!" Expr -> Expr
+  > Expr "//" Expr -> Expr
+  > { Expr "==" Expr -> Expr
+      Expr "!=" Expr -> Expr
+    }
+  > Expr "&&" Expr -> Expr
+  > Expr "||" Expr -> Expr
+  > Expr "->" Expr -> Expr
+  > "if" Expr "then" Expr "else" Expr -> Expr
+  > "assert" Expr ";" Expr -> Expr
+  > "with" Expr ";" Expr -> Expr
+  > Id ":" Expr -> Expr
+  > "{" {Formal ","}* "}" ":" Expr -> Expr
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% Lexical syntax.
+
+module Nix-Lexicals
+exports
+  sorts Id Int Str Path Uri
+  lexical syntax
+    [a-zA-Z\_][a-zA-Z0-9\_\']* -> Id
+    "rec" | "let" | "if" | "then" | "else" | "assert" | "with" | "inherit" -> Id {reject}
+
+    [0-9]+ -> Int
+
+    "\"" (~[\"\\] | ("\\" ~[]) )* "\"" -> Str
+    "''" (~[\"\\] | ("\\" ~[]) )* "''" -> Str
+
+    [a-zA-Z0-9\.\_\-\+]* ("/"[a-zA-Z0-9\.\_\-\+]+)+ -> Path
+
+    [a-zA-Z] [a-zA-Z0-9\+\-\.]* ":" [a-zA-Z0-9\%\/\?\:\@\&\=\+\$\,\-\_\.\!\~\*\']+ -> Uri
+
+  lexical restrictions
+    Id -/- [a-zA-Z0-9\_\']
+    Int -/- [0-9]
+    Path -/- [a-zA-Z0-9\.\_\-\+\/]
+    Uri -/- [a-zA-Z0-9\%\/\?\:\@\&\=\+\$\,\-\_\.\!\~\*\']
+    "rec" "let" "if" "then" "else" "assert" "with" "inherit" -/- [A-Za-z0-9\_\']
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% Layout.
+
+module Nix-Layout
+exports
+  sorts HashComment Asterisk Comment
+  lexical syntax
+    [\ \t\n] -> LAYOUT
+    HashComment -> LAYOUT
+    Comment -> LAYOUT
+    "#" ~[\n]* -> HashComment
+    "/*" ( ~[\*] | Asterisk )* "*/" -> Comment
+    [\*] ~[\/] -> Asterisk
+  lexical restrictions
+    HashComment -/- ~[\n]
+  context-free restrictions
+    LAYOUT? -/- [\ \t\n\#]
+    LAYOUT? -/- [\/].[\*]