public static string Print(UntypedTerm term, bool complex = true)
{
switch (term.Tag)
{
case UntypedTerms.Variable:
{
var variable = (UntypedTerm.Variable)term;
return(variable.Identifier);
}
case UntypedTerms.Lambda:
{
var lambda = (UntypedTerm.Lambda)term;
var body = Print(lambda.Body, complex: false);
return(string.Format("(lambda {0} {1})", lambda.Parameter, body));
}
case UntypedTerms.Apply:
{
var apply = (UntypedTerm.Apply)term;
var @operator = Print(apply.Operator, complex: true);
var operand = Print(apply.Operand, complex: false);
return(string.Format(complex ? "{0} {1}" : "({0} {1})", @operator, operand));
}
default:
throw new ArgumentOutOfRangeException();
}
}
public static UntypedTerm Normalize(UntypedTerm term, Environment <UntypedTerm> environment, ref uint count)
{
switch (term.Tag)
{
case UntypedTerms.Variable:
{
var variable = (UntypedTerm.Variable)term;
return(environment.Lookup(variable.Identifier));
}
case UntypedTerms.Lambda:
{
var lambda = (UntypedTerm.Lambda)term;
var substitution = environment.Maps(lambda.Parameter) ? ("_" + count++) : lambda.Parameter;
environment = environment.Push(lambda.Parameter, new UntypedTerm.Variable(substitution));
var body = Normalize(lambda.Body, environment, ref count);
return(new UntypedTerm.Lambda(substitution, body));
}
case UntypedTerms.Apply:
{
var apply = (UntypedTerm.Apply)term;
var @operator = Normalize(apply.Operator, environment, ref count);
var operand = Normalize(apply.Operand, environment, ref count);
switch (@operator.Tag)
{
case UntypedTerms.Lambda:
var lambda = (UntypedTerm.Lambda)@operator;
environment = environment.Push(lambda.Parameter, operand);
return(Normalize(lambda.Body, environment, ref count));
case UntypedTerms.Variable:
case UntypedTerms.Apply:
return(new UntypedTerm.Apply(@operator, operand));
default:
throw new ArgumentOutOfRangeException();
}
}
default:
throw new ArgumentOutOfRangeException();
}
}
public Apply(UntypedTerm @operator, UntypedTerm operand)
: base(UntypedTerms.Apply)
{
Operator = @operator;
Operand = operand;
}
public Lambda(string parameter, UntypedTerm body)
: base(UntypedTerms.Lambda)
{
Parameter = parameter;
Body = body;
}
public static UntypedTerm Normalize(UntypedTerm term, out uint count)
{
count = 0;
return(Normalize(term, null, ref count));
}