public static IUnboundExpr Match(BindingContext context, MatchExpr expr, IBoundExpr boundValue)
{
// validate the patterns
ShapeChecker.Validate(expr, boundValue.Type);
Coverage.Validate(expr, boundValue.Type);
// convert the cases to vanilla if/then blocks
var valueName = context.NameGenerator.Generate();
var defineValueExpr = new DefineExpr(expr.Value.Position, valueName, expr.Value, false);
var valueExpr = new NameExpr(expr.Value.Position, valueName);
var conditions = new List <DesugaredMatchCase>();
foreach (var matchCase in expr.Cases)
{
var result = new DesugaredMatchCase();
result.Condition = Match(context, boundValue.Type,
matchCase.Pattern, valueExpr, result.Variables);
conditions.Add(result);
}
// build a single compound "if" expression
var ifExpr = (IUnboundExpr)null;
if (expr.Cases.Count == 0)
{
throw new CompileException(expr.Position, "Match expression has no cases.");
}
else if (expr.Cases.Count == 1)
{
// if there is only a since case, and we've ensured exhaustivity already,
// then it must match all values, so just use the body directly
ifExpr = CreateCaseBody(conditions[0].Variables, expr.Cases[0].Body);
}
else
{
// go in reverse order so that we start with the trailing else and build
// forward
for (int i = expr.Cases.Count - 1; i >= 0; i--)
{
if (ifExpr == null)
{
// for the first popped (i.e. last appearing) case, we know it must
// match because the match expression is exhaustive, so just use its
// body directly
ifExpr = CreateCaseBody(conditions[i].Variables, expr.Cases[i].Body);
}
else
{
var body = CreateCaseBody(conditions[i].Variables, expr.Cases[i].Body);
ifExpr = new IfExpr(expr.Cases[i].Position, conditions[i].Condition,
body, ifExpr);
}
}
}
return(new BlockExpr(new IUnboundExpr[] { defineValueExpr, ifExpr }));
}
public static void Validate(MatchExpr expr, IBoundDecl valueType)
{
foreach (var matchCase in expr.Cases)
{
var usedVariables = new Dictionary <string, bool>();
matchCase.Pattern.Accept(new ShapeChecker(valueType, usedVariables));
}
}
IBoundExpr IUnboundExprVisitor<IBoundExpr>.Visit(MatchExpr expr)
{
// bind the value expression
var boundValue = expr.Value.Accept(this);
// convert the patterns to desugared conditional expressions
var desugaredMatch = PatternMatcher.Match(mContext, expr, boundValue);
// bind the desugared form
return desugaredMatch.Accept(this);
}
public static void Validate(MatchExpr expr, IBoundDecl valueType)
{
var coverage = new Coverage(valueType);
foreach (var matchCase in expr.Cases)
{
if (coverage.CoverPattern(matchCase.Pattern))
{
throw new CompileException(matchCase.Position,
"This pattern will never be matched because previous patterns cover it.");
}
}
// make sure the cases are exhaustive
if (!coverage.FullyCovered)
{
throw new CompileException(expr.Position, "Not all possible values will be matched.");
}
}
public virtual IUnboundExpr Transform(MatchExpr expr)
{
return(expr);
}
IUnboundExpr IUnboundExprVisitor <IUnboundExpr> .Visit(MatchExpr expr)
{
throw new NotImplementedException();
}