Synopsis Find unitialized variables in a Pico program.
Examples Uninitialized variables are variables that are used without being initialized. This means that there is a path in the control flow graph from the entry point of the program to a specific use of a variable, where that path does not contain a definition of that variable.

This can be computed as follows:
module demo::lang::Pico::Uninit

import Prelude;
import demo::lang::Pico::Abstract;
import demo::lang::Pico::Load;

import demo::lang::Pico::UseDef;
import demo::lang::Pico::ControlFlow;

import Relation;
import analysis::graphs::Graph;

public set[CFNode] defNodes(PicoId Id, set[Occurrence] Defs) =
   {statement(occ.stat@location, occ.stat) | Occurrence occ <- Defs, == Id};

public set[Occurrence] uninitProgram(PROGRAM P) {
   D = defs(P);                     
   CFG = cflowProgram(P);           
   return { occ | occ <- uses(P),   
                  any(CFNode N <- reachX(CFG.graph, CFG.entry, defNodes(, D)),
                      N has location && occ.location <= N.location) 

public set[Occurrence] uninitProgram(str txt) = uninitProgram(load(txt)); 
First, we determine the variable definitions of the program () and its control flow graph (). Next we ask for every use () of a variable the question: can it be reached from the entries of the program without encountering a definition? This determined as follows:
  • rangeR(D, {occ.item}) is the set of definition for the variable were are looking at. See Rascal:Relation/rangeR.
  • reachX determines the reachability in a graph while excluding certain nodes, see Rascal:Graph/reachX. Here reachX(CFG.graph, CFG.entry, rangeR(D, {occ.item})) determines the nodes in the graph that can be reached from the entry point of the program without passing a definition of the current variable.
  • any(CFNode N <- reachX( ... ), N has location && occ.location <= N.location) yields true if there is such a reachable node that covers the location of the current variable.
  • The complete comprehension () returns the set of occurrences of uninitialized variables.
The function uninitProgram performs this analysis on the source text of a Pico program.

Here is a simple example, where variable p is used without intialization:
rascal>import demo::lang::Pico::Uninit;
rascal>uninitProgram("begin declare n : natural, m : natural, p : natural; n := 10; m := n + p end");
rel[loc location,PicoId name,STATEMENT stat]: {<|file://-|(71,1,<1,71>,<1,72>),"p",asgStat(
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