Ticket 248: Kranc: EDL if/else blocks: Basic functionality.

 - Modify grammar to recognize if/else. (Code by Steve Brandt)
 - Use IfThen operators for equations guarded by if/else.

Auxiliary/Grammars/kranc2.peg

@@ -43,7 +43,8 @@ ifexpr = if {cexpr} then {mexpr} else {mexpr}
 eqn = ({dtensor}|{tensor}) \= {expr}{-end}
 doper = {dname}{indices}
 deqn = {doper} {barename} \= {expr}{-end}
-eqns = {eqn}( {eqn})*
+ifblock = if \( {cexpr} \) \{ {eqns} \}( else \{ {eqns} \}|)|{eqn}
+eqns = {ifblock}( {ifblock})*
 deqns = {deqn}( {deqn})*
 at_or_in = (at|in)
 on_clause = on {uname}

Tools/CodeGen/KrancScript.m

@@ -142,7 +142,7 @@
 
 process[calc:"calculation"[content___]] :=
   Module[
-    {name,eqs,joinWord,where},
+    {name,eqs,joinWord,where,dbeq},
     name = Cases[calc, "uname"[n_]:>n][[1]];
     eqs = Cases[calc, "eqns"[es___]:>{es}][[1]];
 
@@ -160,11 +160,51 @@
                   StringMatchQ[schedule,"analysis",IgnoreCase->True],
                   "at","in"];
 
+    dbeq = process["eqns"[eqs]];
+
+    (*  Use IfThen operator for assignments in if/else blocks.  *)
+    Module[{ condstack = {True}, currPred = True, varsCondAs = {} },
+
+      (* Replace assignments delineated by ChemoraIfBlock markers with Kranc
+         IfThen things. *)
+      dbeq = 
+         ( # /. 
+           { ( v_ -> ChemoraIfBlockStart[e_] ) :> 
+                ( condstack = Join[condstack,{currPred,v}];
+                  currPred = ChemoraOpAnd[currPred, v];
+                  v -> e ),
+             ( _ -> ChemoraIfBlockElseMarker[] ) :>
+                ( currPred = ChemoraOpAnd[condstack[[-2]], ! condstack[[-1]]];
+                  {} ),
+             ( _ -> ChemoraIfBlockEnd[] ) :>
+                ( currPred = condstack[[-2]];
+                  condstack = Drop[condstack,-2];
+                  {} ),
+             ( v_ -> e_ ) :>
+                If[ currPred === True,
+                    v -> e,
+                    AppendTo[varsCondAs,v];
+                       v -> IfThen[currPred,e,v] ]
+             } )& /@ dbeq // Flatten;
+
+      (* Initialize variables assigned in if/else blocks to avoid
+         the use of an uninitialized variable in the first IfThen construct
+         for a variable. *)
+      dbeq = Join[ # -> 0 & /@ Union[varsCondAs], dbeq ];
+
+      dbeq = dbeq  //. ChemoraOpAnd[True,v_] -> v;
+      ];
+
     {Name -> name,
-     Equations -> Map[process,eqs],
+     Equations -> dbeq,
      Schedule -> {joinWord<>" "<>schedule},
      Where -> where}];
 
+process["eqns"[]] := {}
+process["eqns"[ifbl:"ifblock"[___],more___]] :=
+   { process[ifbl],process["eqns"[more]] }
+process["eqns"[eqs_List]] := Flatten[ process /@ eqs ];
+
 process["eqn"[lhs_,rhs_]] := Module[{name,eqs}, process[lhs] -> process[rhs]];
 (*
 process["tensor"["name"["Opast"],"indices"[ind___],follow___]] := Print["ind=",InputForm[ind]," follow=",InputForm[follow]];
@@ -261,6 +301,24 @@
 process["ifexpr"[cond_, opt1_, opt2_]] :=
    IfThen[ process[cond], process[opt1], process[opt2] ];
 
+chemoraIntermediateCount = 0;
+chemoraMakeIntermediate[]:=
+     "chemoraIntermediate" <> ToString[chemoraIntermediateCount++];
+
+process["ifblock"[cexpr:"cexpr"[_],eqif:"eqns"[___],eqelse:"eqns"[___]]] :=
+   { chemoraMakeIntermediate[] -> ChemoraIfBlockStart[process[cexpr]],
+     process[eqif],
+     chemoraMakeIntermediate[] -> ChemoraIfBlockElseMarker[],
+     process[eqelse],
+     chemoraMakeIntermediate[] -> ChemoraIfBlockEnd[] }
+
+process["ifblock"[cexpr:"cexpr"[_],eqif:"eqns"[___]]] :=
+     { chemoraMakeIntermediate[] -> ChemoraIfBlockStart[process[cexpr]],
+       process[eqif],
+       chemoraMakeIntermediate[] -> ChemoraIfBlockEnd[] }
+
+process["ifblock"[eqn_]] := process[eqn];
+
 process["coexpr"["cexpr"[cexpr__]]] := process["cexpr"[cexpr]];
 
 process["cexpr"[Longest[v1__], "logop"["or"], v2__]] :=