internal Expression Parse(string function)
{
var z = new ParserResult { Input = function.Replace(" ", ""), Output = null };
/*
* number = {"0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"}
* factor = number | "(" expression ")"
* component = factor [{("*" | "/") factor}]
* expression = component [{("+" | "-") component}]
*/
ParserFunction expression = null;
ParserFunction number = null;
ParserFunction factor = null;
ParserFunction component = null;
number = input => digit(input);
factor = input => from i in number(input)
select i;
component = input => (from i in factor(input)
from k in mul(i)
from o in factor(k)
select k.ExpressionType == ExpressionType.Multiply || k.ExpressionType == ExpressionType.Divide
? new ParserResult
{
ExpressionType = k.ExpressionType,
Input = o.Input,
Output = o.Output != null && i.Output != null
?
Expression.MakeBinary(k.ExpressionType,
i.Output,
o.Output)
: null
}
: new ParserResult
{
Input = input.Input,
Output = null,
ExpressionType = ExpressionType.Quote
}
)
.OR
(
from k in mul(input)
from o in factor(k)
select k.ExpressionType == ExpressionType.Multiply || k.ExpressionType== ExpressionType.Divide
?
new ParserResult
{
ExpressionType = k.ExpressionType,
Input = o.Input,
Output = o.Output != null && input.Output != null
?
Expression.MakeBinary(k.ExpressionType,
input.Output,
o.Output)
: null
}
: new ParserResult
{
Input = input.Input,
Output = null,
ExpressionType = ExpressionType.Quote
}
)
.OR
(
from u in factor(input)
select u
)
.OR
(
from u in input
select u
);
expression = input => (from i in component(input)
from k in add(i)
from o in component(k)
select new ParserResult
{
ExpressionType = k.ExpressionType,
Input = o.Input,
Output = o.Output != null && i.Output != null
? Expression.MakeBinary(k.ExpressionType, i.Output,
o.Output)
: null
})
.OR
(
from i in component(input)
select i
)
.OR
(
from i in input
select i
);
ParserResult all = from o in Repeat(expression, z)
select o;
return all.Output;
}
public static ParserResult Repeat(ParserFunction function, ParserResult parser)
{
ParserResult result = function(parser);
if (!String.IsNullOrEmpty(result.Input))
return Repeat(function, result);
return result;
}