public static bool ContainsBoundSymbol(Expression expression, SymbolRef symbol)
{
if (expression is BoundSymbolExpression)
{
var boundSymbol = (BoundSymbolExpression)expression;
if (boundSymbol.Symbol == symbol)
return true;
else
return false;
}
else if (expression is AbstractionExpression)
{
var abstraction = (AbstractionExpression)expression;
if (abstraction.Left != symbol)
return ContainsBoundSymbol(abstraction.Right, symbol);
else
return false;
}
else if (expression is ApplicationExpression)
{
var application = (ApplicationExpression)expression;
if (ContainsBoundSymbol(application.Left, symbol))
return true;
return ContainsBoundSymbol(application.Right, symbol);
}
else if (expression is BuiltinExpression)
{
var builtin = (BuiltinExpression)expression;
if (ContainsBoundSymbol(builtin.Left, symbol))
return true;
return ContainsBoundSymbol(builtin.Right, symbol);
}
else
{
return false;
}
}
public static Expression Substitute(Expression expression, SymbolRef symbol, Expression replacement)
{
if (expression is BoundSymbolExpression)
{
var boundSymbol = (BoundSymbolExpression)expression;
if (boundSymbol.Symbol == symbol)
return replacement;
else
return expression;
}
else if (expression is AbstractionExpression)
{
var abstraction = (AbstractionExpression)expression;
if (abstraction.Left != symbol)
return new AbstractionExpression { Left = abstraction.Left, Right = Substitute(abstraction.Right, symbol, replacement) };
else
return expression;
}
else if (expression is ApplicationExpression)
{
var application = (ApplicationExpression)expression;
return new ApplicationExpression { Left = Substitute(application.Left, symbol, replacement), Right = Substitute(application.Right, symbol, replacement) };
}
else if (expression is BuiltinExpression)
{
var builtin = (BuiltinExpression)expression;
return new BuiltinExpression { Left = Substitute(builtin.Left, symbol, replacement), Right = Substitute(builtin.Right, symbol, replacement), Display = builtin.Display, Evaluate = builtin.Evaluate };
}
else
{
return expression;
}
}