/// Parses an ExprTree into Tru abstract syntax.
public static new TruExpr Parse(ExprTree expr)
{
if (expr is ExprLiteral exprLit)
{
if (ExprTree.Match("true", exprLit))
{
return(new TruBool(true));
}
else if (ExprTree.Match("false", exprLit))
{
return(new TruBool(false));
}
else
{
return(TruId.Parse(exprLit));
}
}
else if (expr is ExprList exprList && exprList.list.Length > 0) // cast expr into exprList
{
if (ExprTree.Match("{lambda {LITERAL ...} ANY}", exprList))
{
ExprTree[] parameters = ((ExprList)exprList.list[1]).list;
return(new TruLambda(
Helpers.ArrayMap(parameters, (p) => TruId.Parse(p).name), // Will throw error if contains an invalid id.
TruExpr.Parse(exprList.list[2])
));
}
else if (ExprTree.Match("{let {[LITERAL ANY] ...} ANY}", exprList))
{
ExprList[] localExpr = Helpers.ArrayMap(((ExprList)exprList.list[1]).list, (x) => (ExprList)x);
(string, TruExpr)[] locals = Helpers.ArrayMap(localExpr, // Convert into name, expr tuples.
/// Parses an ExprTree into Tru abstract syntax that can be Executed.
public static TruStatement Parse(ExprTree expr)
{
if (expr is ExprList exprList && exprList.list.Length > 0) // cast expr into exprList
{
if (ExprTree.Match("{define LITERAL ANY}", exprList))
{
return(new TruDef(TruId.Parse(exprList.list[1]).name, TruExpr.Parse(exprList.list[2])));
}
else if (ExprTree.Match("{define {LITERAL LITERAL ...} ANY}", exprList))
{
ExprTree[] signature = ((ExprList)exprList.list[1]).list;
string[] paramaters = new string[signature.Length - 1]; // put all but first element into parameters as strings
for (int i = 0; i < paramaters.Length; i++)
{
paramaters[i] = TruId.Parse(signature[i + 1]).name;
}
return(new TruDef(TruId.Parse(signature[0]).name,
new TruLambda(paramaters, TruExpr.Parse(exprList.list[2]))
));
}
}
// If not a define statement, its an expression.
return(TruExpr.Parse(expr));
}
private static bool MatchHelper(ExprTree pattern, ExprTree expr)
{
if (pattern is ExprLiteral patternLit)
{
return(patternLit.val == "ANY" ||
(patternLit.val == "LITERAL" && expr is ExprLiteral) ||
(patternLit.val == "LIST" && expr is ExprList) ||
pattern.Equals(expr));
}
else if (pattern is ExprList patList && expr is ExprList exprList)
{
int patI = patList.list.Length - 1, exprI = exprList.list.Length - 1;
while (patI >= 0) // Loop through the lists backwards so that ... is visited before what it affects.
// If a ... has nothing before it just match it like a normal symbol
{
if (patList.list[patI].Equals(new ExprLiteral("...")) && patI >= 1)
{
ExprTree repPattern = patList.list[patI - 1];
int matchCount = 0;
for (/*exprI current value*/; exprI >= 0 && MatchHelper(repPattern, exprList.list[exprI]); exprI--)
{
matchCount++;
}
patI -= 2;
// to prevent ... from eating the first a in {a a ...}, we count repetitions of the pattern in pattern
// and make sure we found at least that many.
int expectedCount = 0;
for (/*patI current value*/; patI >= 0 && patList.list[patI].Equals(repPattern); patI--)
{
expectedCount++;
}
if (expectedCount > matchCount)
{
return(false);
}
}
else
{
if (exprI < 0 || !MatchHelper(patList.list[patI], exprList.list[exprI]))
{
return(false);
}
patI--; exprI--;
}
}
return(patI < 0 && exprI < 0);
}
/// Parses a string into a list of TruStatements.
public static TruStatement[] ParseAll(string code)
{
return(Helpers.ArrayMap(ExprTree.ParseAll(code), TruStatement.Parse));
}
/// Parses a string into Tru abstract syntax that can be Executed.
public static TruStatement Parse(string code)
{
return(TruStatement.Parse(ExprTree.Parse(code)));
}
/// Parses a string into Tru abstract syntax that can be interpreted.
public static new TruExpr Parse(string code)
{
return(TruExpr.Parse(ExprTree.Parse(code)));
}
/// Checks if expr matches pattern, meaning it has the same structure,
/// Special tags can be used in the pattern as wildcards:
/// ANY : matches any ExprTree
/// LITERAL : matches any ExprLiteral
/// LIST : matches any ExrList
/// ... : Modifies the previous item to match 0 or more repetitions of the previous pattern in a list.
public static bool Match(string pattern, ExprTree expr)
{
return(MatchHelper(Parse(pattern), expr));
}
