public T Visit <A>(IRecExpression <A> rec) where A : Expression
{
rec.Input.Accept(this);
rec.Start.Accept(this);
rec.Step.Accept(this);
return(default(T));
}
public Expression Visit <A>(IRecExpression <A> rec) where A : Expression
{
var input = (NumExpression)rec.Input.Accept(this);
var start = (A)rec.Start.Accept(this);
if (rec.NumVariableName != VariableName && rec.AccVariableName != VariableName)
{
var step = (A)rec.Step.Accept(this);
return(rec.Construct(input, start, rec.NumVariableName, rec.AccVariableName, step));
}
else // our variable is shadowed by one of the two binders in rec
{
return(rec.Construct(input, start, rec.NumVariableName, rec.AccVariableName, rec.Step));
}
}
public SortedSet <string> Visit <A>(IRecExpression <A> rec) where A : Expression
{
// First find free variables in the step
var vars = Run(rec.Step);
// Then remove binders
vars.Remove(rec.NumVariableName);
vars.Remove(rec.AccVariableName);
// Now add free variables from input and step
vars.UnionWith(Run(rec.Input));
vars.UnionWith(Run(rec.Start));
return(vars);
}
public async Task <Value> Visit <A>(IRecExpression <A> rec) where A : Expression
{
// A rec has an input, a start, and a step, which itself has two free vars
// The idea is to find out what value the input is.
// if it is zero we return the start
// otherwise we evaluate the rec with an input one less, then put this through the step
Value input = await Run(rec.Input); // we need this
if (input is NumValue)
{
NumValue num = input as NumValue;
if (num.Value == 0)
{
return(await Run(rec.Start));
}
else
{
// this looks bad. Fix it
int predecessor = num.Value - 1;
NumValue newNum = new NumValue(predecessor);
VariableSubstituter substNum = new VariableSubstituter(rec.NumVariableName, new NumConstant(predecessor));
Expression newRec = rec.Construct(new NumConstant(predecessor), rec.Start, rec.NumVariableName,
rec.AccVariableName, rec.Step);
VariableSubstituter substAcc = new VariableSubstituter(rec.AccVariableName, newRec);
Expression temp = substNum.Substitute(rec.Step);
Expression temp2 = substAcc.Substitute(temp);
return(await Run(temp2));
}
}
else
{
throw new ArgumentException("In rec the input should evaluate to a Num");
}
throw new NotImplementedException();
}
