public IExpression Parse(string value)
{
ParserContext ctx = new ParserContext(value, 0);
return(GetExpression(ctx));
}
private bool skipASymbol(ParserContext context)
{
return(skipIf((c) => true, context));
}
private bool skipWhiteSpace(ParserContext context)
{
return(skipWhile((c) => char.IsWhiteSpace(c), context));
}
private bool skipCharacter(char toSkip, ParserContext context)
{
return(skipIf((c) => c == toSkip, context));
}
private IExpression GetUnary(ParserContext ctx)
{
skipWhiteSpace(ctx);
if (ctx.CurrentPosition == ctx.Text.Length)
{
//throw exception
}
if (skipCharacter('!', ctx))
{
skipWhiteSpace(ctx);
return(new Negation(GetUnary(ctx)));
}
if (skipCharacter('(', ctx))
{
var saveCtx = ctx.Clone();
try
{
var expr = GetExpression(ctx);
if (expr is IMath)
{
ctx = saveCtx;
ctx.CurrentPosition--;
return(GetPredicate(ctx));
}
else
{
skipASymbol(ctx);
return(expr);
}
}
catch
{
}
ctx.CurrentPosition = saveCtx.CurrentPosition - 1;
return(GetPredicate(ctx));
}
var prevChar = ctx.Text[ctx.CurrentPosition];
if (skipCharacter('@', ctx) || skipCharacter('?', ctx))
{
var value = "";
while (ctx.CurrentPosition != ctx.Text.Length && (char.IsLower(ctx.Text[ctx.CurrentPosition]) ||
char.IsDigit(ctx.Text[ctx.CurrentPosition])))
{
value += ctx.Text[ctx.CurrentPosition];
skipASymbol(ctx);
}
var constant = new Variable(value);
if (prevChar == '@')
{
skipWhiteSpace(ctx);
return(new Universal(constant, GetUnary(ctx)));
}
else
{
skipWhiteSpace(ctx);
return(new Existence(constant, GetUnary(ctx)));
}
}
skipWhiteSpace(ctx);
return(GetPredicate(ctx));
}