work in progress: new implementation for 'a[^1]'

compiler/ast.nim

@@ -1017,16 +1017,11 @@ proc add*(father, son: PNode) =
 
 type Indexable = PNode | PType
 
-template `[]`*(n: Indexable, i: int): Indexable =
-  n.sons[i]
+template `[]`*(n: Indexable, i: int): Indexable = n.sons[i]
+template `[]=`*(n: Indexable, i: int; x: Indexable) = n.sons[i] = x
 
-template `-|`*(b, s: untyped): untyped =
-  (if b >= 0: b else: s.len + b)
-
-# son access operators with support for negative indices
-template `{}`*(n: Indexable, i: int): untyped = n[i -| n]
-template `{}=`*(n: Indexable, i: int, s: Indexable) =
-  n.sons[i -| n] = s
+template `[]`*(n: Indexable, i: BackwardsIndex): Indexable = n[n.len - i.int]
+template `[]=`*(n: Indexable, i: BackwardsIndex; x: Indexable) = n[n.len - i.int] = x
 
 when defined(useNodeIds):
   const nodeIdToDebug* = -1 # 299750 # 300761 #300863 # 300879

compiler/cgendata.nim

@@ -154,7 +154,7 @@ proc includeHeader*(this: BModule; header: string) =
 
 proc s*(p: BProc, s: TCProcSection): var Rope {.inline.} =
   # section in the current block
-  result = p.blocks[^1].sections[s]
+  result = p.blocks[p.blocks.len-1].sections[s]
 
 proc procSec*(p: BProc, s: TCProcSection): var Rope {.inline.} =
   # top level proc sections

compiler/parser.nim

@@ -1905,7 +1905,7 @@ proc parseVariable(p: var TParser): PNode =
   #| variable = (varTuple / identColonEquals) colonBody? indAndComment
   if p.tok.tokType == tkParLe: result = parseVarTuple(p)
   else: result = parseIdentColonEquals(p, {withPragma, withDot})
-  result{-1} = postExprBlocks(p, result{-1})
+  result[^1] = postExprBlocks(p, result[^1])
   indAndComment(p, result)
 
 proc parseBind(p: var TParser, k: TNodeKind): PNode =

compiler/semexprs.nim

@@ -1665,7 +1665,7 @@ proc semQuoteAst(c: PContext, n: PNode): PNode =
   # We transform the do block into a template with a param for
   # each interpolation. We'll pass this template to getAst.
   var
-    quotedBlock = n{-1}
+    quotedBlock = n[^1]
     op = if n.len == 3: expectString(c, n[1]) else: "``"
     quotes = newSeq[PNode](1)
       # the quotes will be added to a nkCall statement

compiler/semobjconstr.nim

@@ -78,13 +78,13 @@ proc caseBranchMatchesExpr(branch, matched: PNode): bool =
 
 proc pickCaseBranch(caseExpr, matched: PNode): PNode =
   # XXX: Perhaps this proc already exists somewhere
-  let endsWithElse = caseExpr{-1}.kind == nkElse
+  let endsWithElse = caseExpr[^1].kind == nkElse
   for i in 1 .. caseExpr.len - 1 - int(endsWithElse):
     if caseExpr[i].caseBranchMatchesExpr(matched):
       return caseExpr[i]
 
   if endsWithElse:
-    return caseExpr{-1}
+    return caseExpr[^1]
 
 iterator directFieldsInRecList(recList: PNode): PNode =
   # XXX: We can remove this case by making all nkOfBranch nodes
@@ -136,17 +136,20 @@ proc semConstructFields(c: PContext, recNode: PNode,
 
   of nkRecCase:
     template fieldsPresentInBranch(branchIdx: int): string =
-      fieldsPresentInInitExpr(recNode[branchIdx]{-1}, initExpr)
+      let branch = recNode[branchIdx]
+      let fields = branch[branch.len - 1]
+      fieldsPresentInInitExpr(fields, initExpr)
 
     template checkMissingFields(branchNode: PNode) =
-      checkForMissingFields(branchNode{-1}, initExpr)
+      let fields = branchNode[branchNode.len - 1]
+      checkForMissingFields(fields, initExpr)
 
     let discriminator = recNode.sons[0];
     internalAssert discriminator.kind == nkSym
     var selectedBranch = -1
 
     for i in 1 ..< recNode.len:
-      let innerRecords = recNode[i]{-1}
+      let innerRecords = recNode[i][^1]
       let status = semConstructFields(c, innerRecords, initExpr, flags)
       if status notin {initNone, initUnknown}:
         mergeInitStatus(result, status)
@@ -250,7 +253,7 @@ proc semObjConstr(c: PContext, n: PNode, flags: TExprFlags): PNode =
   var t = semTypeNode(c, n.sons[0], nil)
   result = newNodeIT(nkObjConstr, n.info, t)
   for child in n: result.add child
-  
+
   t = skipTypes(t, {tyGenericInst, tyAlias})
   if t.kind == tyRef: t = skipTypes(t.sons[0], {tyGenericInst, tyAlias})
   if t.kind != tyObject:

compiler/semstmts.nim

@@ -823,7 +823,7 @@ proc typeSectionLeftSidePass(c: PContext, n: PNode) =
     a.sons[0] = newSymNode(s)
 
 proc checkCovariantParamsUsages(genericType: PType) =
-  var body = genericType{-1}
+  var body = genericType[^1]
 
   proc traverseSubTypes(t: PType): bool =
     template error(msg) = localError(genericType.sym.info, msg)

compiler/semtypes.nim

@@ -1618,8 +1618,8 @@ proc semGenericParamList(c: PContext, n: PNode, father: PType = nil): PNode =
     var a = n.sons[i]
     if a.kind != nkIdentDefs: illFormedAst(n)
     let L = a.len
-    var def = a{-1}
-    let constraint = a{-2}
+    var def = a[^1]
+    let constraint = a[^2]
     var typ: PType
 
     if constraint.kind != nkEmpty: