the delegator pragma becomes a set of dot operators

compiler/ast.nim

@@ -409,7 +409,9 @@ type
                 # efficiency
     nfTransf,   # node has been transformed
     nfSem       # node has been checked for semantics
-    nfDelegate  # the call can use a delegator
+    nfDotField  # the call can use a dot operator
+    nfDotSetter # the call can use a setter dot operarator
+    nfExplicitCall # x.y() was used instead of x.y
     nfExprCall  # this is an attempt to call a regular expression
     nfIsRef     # this node is a 'ref' node; used for the VM
 
@@ -843,7 +845,8 @@ const
   ExportableSymKinds* = {skVar, skConst, skProc, skMethod, skType, skIterator, 
     skMacro, skTemplate, skConverter, skEnumField, skLet, skStub}
   PersistentNodeFlags*: TNodeFlags = {nfBase2, nfBase8, nfBase16,
-                                      nfAllConst, nfDelegate, nfIsRef}
+                                      nfDotSetter, nfDotField,
+                                      nfAllConst,nfIsRef}
   namePos* = 0
   patternPos* = 1    # empty except for term rewriting macros
   genericParamsPos* = 2
@@ -1044,6 +1047,10 @@ proc newStrNode(kind: TNodeKind, strVal: string): PNode =
   result = newNode(kind)
   result.strVal = strVal
 
+proc withInfo*(n: PNode, info: TLineInfo): PNode =
+  n.info = info
+  return n
+
 proc newIdentNode(ident: PIdent, info: TLineInfo): PNode = 
   result = newNode(nkIdent)
   result.ident = ident

compiler/parser.nim

@@ -281,7 +281,7 @@ proc parseSymbol(p: var TParser): PNode =
         add(result, newIdentNodeP(getIdent"{}", p))
         getTok(p)
         eat(p, tkCurlyRi)
-      of tokKeywordLow..tokKeywordHigh, tkSymbol, tkOpr, tkDotDot:
+      of tokKeywordLow..tokKeywordHigh, tkSymbol, tkOpr, tkDot, tkDotDot:
         add(result, newIdentNodeP(p.tok.ident, p))
         getTok(p)
       of tkIntLit..tkCharLit:

compiler/semcall.nim

@@ -82,7 +82,7 @@ proc notFoundError*(c: PContext, n: PNode, errors: seq[string]) =
     # fail fast:
     globalError(n.info, errTypeMismatch, "")
   var result = msgKindToString(errTypeMismatch)
-  add(result, describeArgs(c, n, 1 + ord(nfDelegate in n.flags)))
+  add(result, describeArgs(c, n, 1 + ord(nfDotField in n.flags)))
   add(result, ')')
   
   var candidates = ""
@@ -138,15 +138,33 @@ proc resolveOverloads(c: PContext, n, orig: PNode,
 
   let overloadsState = result.state
   if overloadsState != csMatch:
-    if nfDelegate in n.flags:
+    if nfDotField in n.flags:
-      internalAssert f.kind == nkIdent
+      internalAssert f.kind == nkIdent and n.sonsLen >= 2
-      let calleeName = newStrNode(nkStrLit, f.ident.s)
+      let calleeName = newStrNode(nkStrLit, f.ident.s).withInfo(n.info)
-      calleeName.info = n.info
 
-      let callOp = newIdentNode(idDelegator, n.info)
+      # leave the op head symbol empty,
-      n.sons[0..0] = [callOp, calleeName]
+      # we are going to try multiple variants
-      orig.sons[0..0] = [callOp, calleeName]
+      n.sons[0..1] = [nil, n[1], calleeName]
+      orig.sons[0..1] = [nil, orig[1], calleeName]
       
+      template tryOp(x) =
+        let op = newIdentNode(getIdent(x), n.info)
+        n.sons[0] = op
+        orig.sons[0] = op
+        pickBest(op)
+
+      if nfExplicitCall in n.flags:
+        tryOp ".()"
+   
+      if result.state in {csEmpty, csNoMatch}:
+        tryOp "."
+
+    elif nfDotSetter in n.flags:
+      internalAssert f.kind == nkIdent and n.sonsLen == 3
+      let calleeName = newStrNode(nkStrLit, f.ident.s[0.. -2]).withInfo(n.info)
+      let callOp = newIdentNode(getIdent".=", n.info)
+      n.sons[0..1] = [callOp, n[1], calleeName]
+      orig.sons[0..1] = [callOp, orig[1], calleeName]
       pickBest(callOp)
     
     if overloadsState == csEmpty and result.state == csEmpty:

compiler/semexprs.nim

@@ -694,6 +694,7 @@ proc semIndirectOp(c: PContext, n: PNode, flags: TExprFlags): PNode =
       # it is a static call!
       result = n.sons[0]
       result.kind = nkCall
+      result.flags.incl nfExplicitCall
       for i in countup(1, sonsLen(n) - 1): addSon(result, n.sons[i])
       return semExpr(c, result, flags)
   else:
@@ -999,7 +1000,7 @@ proc dotTransformation(c: PContext, n: PNode): PNode =
   else:
     var i = considerAcc(n.sons[1])
     result = newNodeI(nkDotCall, n.info)
-    result.flags.incl nfDelegate
+    result.flags.incl nfDotField
     addSon(result, newIdentNode(i, n[1].info))
     addSon(result, copyTree(n[0]))
   
@@ -1082,12 +1083,13 @@ proc semArrayAccess(c: PContext, n: PNode, flags: TExprFlags): PNode =
 
 proc propertyWriteAccess(c: PContext, n, nOrig, a: PNode): PNode =
   var id = considerAcc(a[1])
-  let setterId = newIdentNode(getIdent(id.s & '='), n.info)
+  var setterId = newIdentNode(getIdent(id.s & '='), n.info)
   # a[0] is already checked for semantics, that does ``builtinFieldAccess``
   # this is ugly. XXX Semantic checking should use the ``nfSem`` flag for
   # nodes?
   let aOrig = nOrig[0]
   result = newNode(nkCall, n.info, sons = @[setterId, a[0], semExpr(c, n[1])])
+  result.flags.incl nfDotSetter
   let orig = newNode(nkCall, n.info, sons = @[setterId, aOrig[0], nOrig[1]])
   result = semOverloadedCallAnalyseEffects(c, result, orig, {})
   
@@ -1777,22 +1779,6 @@ proc semBlock(c: PContext, n: PNode): PNode =
   closeScope(c)
   dec(c.p.nestedBlockCounter)
 
-proc buildCall(n: PNode): PNode =
-  if n.kind == nkDotExpr and n.len == 2:
-    # x.y --> y(x)
-    result = newNodeI(nkCall, n.info, 2)
-    result.sons[0] = n.sons[1]
-    result.sons[1] = n.sons[0]
-  elif n.kind in nkCallKinds and n.sons[0].kind == nkDotExpr:
-    # x.y(a) -> y(x, a)
-    let a = n.sons[0]
-    result = newNodeI(nkCall, n.info, n.len+1)
-    result.sons[0] = a.sons[1]
-    result.sons[1] = a.sons[0]
-    for i in 1 .. <n.len: result.sons[i+1] = n.sons[i]
-  else:
-    result = n
-
 proc doBlockIsStmtList(n: PNode): bool =
   result = n.kind == nkDo and
            n[paramsPos].sonsLen == 1 and
@@ -1901,7 +1887,7 @@ proc semExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
   of nkCall, nkInfix, nkPrefix, nkPostfix, nkCommand, nkCallStrLit: 
     # check if it is an expression macro:
     checkMinSonsLen(n, 1)
-    let mode = if nfDelegate in n.flags: {} else: {checkUndeclared}
+    let mode = if nfDotField in n.flags: {} else: {checkUndeclared}
     var s = qualifiedLookUp(c, n.sons[0], mode)
     if s != nil: 
       if gCmd == cmdPretty and n.sons[0].kind == nkDotExpr:
@@ -1940,7 +1926,7 @@ proc semExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
       # the 'newSeq[T](x)' bug
       setGenericParams(c, n.sons[0])
       result = semDirectOp(c, n, flags)
-    elif isSymChoice(n.sons[0]) or nfDelegate in n.flags:
+    elif isSymChoice(n.sons[0]) or nfDotField in n.flags:
       result = semDirectOp(c, n, flags)
     else:
       result = semIndirectOp(c, n, flags)

doc/manual.txt

@@ -4106,6 +4106,59 @@ types that will match the typedesc param:
 
 The constraint can be a concrete type or a type class.
 
+Special Operators
+=================
+
+dot operators
+-------------
+
+Nimrod offers a special family of dot operators that can be used to
+intercept and rewrite proc call and field access attempts, referring
+to previously undeclared symbol names. They can be used to provide a
+fluent interface to objects lying outside the static confines of the
+Nimrod's type system such as values from dynamic scripting languages
+or dynamic file formats such as JSON or XML.
+
+When Nimrod encounters an expression that cannot be resolved by the
+standard overload resolution rules, the current scope will be searched
+for a dot operator that can be matched against a re-written form of
+the expression, where the unknown field or proc name is converted to
+an additional static string parameter:
+
+.. code-block:: nimrod
+  a.b # becomes `.`(a, "b")
+  a.b(c, d) # becomes `.`(a, "b", c, d)
+
+The matched dot operators can be symbols of any callable kind (procs,
+templates and macros), depending on the desired effect:
+
+.. code-block:: nimrod
+  proc `.` (js: PJsonNode, field: string): JSON = js[field]
+
+  var js = parseJson("{ x: 1, y: 2}")
+  echo js.x # outputs 1
+  echo js.y # outputs 2
+
+The following dot operators are available:
+
+operator `.`
+------------ 
+This operator will be matched against both field accesses and method calls.
+
+operator `.()`
+---------------
+This operator will be matched exclusively against method calls. It has higher
+precedence than the `.` operator and this allows you to handle expressions like
+`x.y` and `x.y()` differently if you are interfacing with a scripting language
+for example.
+
+operator `.=`
+-------------
+This operator will be matched against assignments to missing fields.
+
+.. code-block:: nimrod
+  a.b = c # becomes `.=`(a, "b", c)
+
 
 Term rewriting macros
 =====================
@@ -4758,42 +4811,6 @@ This may change in future versions of language, but for now use
 the ``finalizer`` parameter to ``new``.
 
 
-delegator pragma
-----------------
-
-**Note**: The design of the delegator feature is subject to change.
-
-The delegator pragma can be used to intercept and rewrite proc call and field
-access attempts referring to previously undeclared symbol names. It can be used
-to provide a fluent interface to objects lying outside the static confines of
-the Nimrod's type system such as values from dynamic scripting languages or
-dynamic file formats such as JSON or XML.
-
-A delegator is a special form of the `()` operator marked with the delagator
-pragma. When Nimrod encounters an expression that cannot be resolved by the
-standard overload resolution, any delegators in the current scope will be
-matched against a rewritten form of the expression following the standard
-signature matching rules. In the rewritten expression, the name of the unknown
-proc or field name is inserted as an additional static string parameter always
-appearing in the leading position:
-
-.. code-block:: nimrod
-  a.b => delegator("b", a)
-  a.b(c, d) => delegator("b", a, c)
-  a b, c, d => delegator("a", b, c, d)
-
-
-The delegators can be any callable symbol type (procs, templates, macros)
-depending on the desired effect:
-
-.. code-block:: nimrod
-  proc `()` (field: string, js: PJsonNode): JSON {.delegator.} = js[field]
-
-  var js = parseJson("{ x: 1, y: 2}")
-  echo js.x # outputs 1
-  echo js.y # outputs 2
-
-
 procvar pragma
 --------------
 The `procvar`:idx: pragma is used to mark a proc that it can be passed to a

tests/specialops/tdotops.nim

@@ -0,0 +1,66 @@
+discard """
+  output: '''
+10
+assigning z = 20
+reading field y
+20
+call to y
+dot call
+no params call to a
+100
+no params call to b
+100
+one param call to c with 10
+100'''
+"""
+
+type
+  T1 = object
+    x*: int
+
+  TD = distinct T1
+
+  T2 = object
+    x: int
+
+proc `.`*(v: T1, f: string): int =
+  echo "reading field ", f
+  return v.x
+
+proc `.=`(x: var T1, f: string{lit}, v: int) =
+  echo "assigning ", f, " = ", v
+  x.x = v
+
+template `.()`(x: T1, f: string, args: varargs[expr]): string =
+  echo "call to ", f
+  "dot call"
+
+echo ""
+
+var t = T1(x: 10)
+
+echo t.x
+t.z = 20
+echo t.y
+echo t.y()
+
+var d = TD(t)
+assert(not compiles(d.y))
+
+proc `.`(v: T2, f: string): int =
+  echo "no params call to ", f
+  return v.x
+
+proc `.`*(v: T2, f: string, a: int): int =
+  echo "one param call to ", f, " with ", a
+  return v.x
+
+var tt = T2(x: 100)
+
+echo tt.a
+echo tt.b()
+echo tt.c(10)
+
+assert(not compiles(tt.d("x")))
+assert(not compiles(tt.d(1, 2)))
+

web/news.txt

@@ -68,8 +68,8 @@ Language Additions
 - Exported templates are allowed to access hidden fields.
 - The ``using statement`` enables you to more easily author domain-specific
   languages and libraries providing OOP-like syntactic sugar.
-- Added a new ``delegator pragma`` for handling calls to missing procs and
+- Added the possibility to override various dot operators in order to handle
-  fields at compile-time.
+  calls to missing procs and reads from undeclared fields at compile-time.
 - The overload resolution now supports ``static[T]`` params that must be
   evaluable at compile-time.
 - Support for user-defined type classes has been added.