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 }));
}
IBoundExpr IUnboundExprVisitor<IBoundExpr>.Visit(IfExpr expr)
{
var bound = new BoundIfExpr(
expr.Condition.Accept(this),
expr.ThenBody.Accept(this),
(expr.ElseBody == null) ? null : expr.ElseBody.Accept(this));
if (bound.Condition.Type != Decl.Bool)
{
throw new CompileException(expr.Position, String.Format(
"Condition of if/then/else is returning type {0} but should be Bool.",
bound.Condition.Type));
}
if (bound.ElseBody != null)
{
// has an else, so make sure both arms match
if (!DeclComparer.TypesMatch(bound.ThenBody.Type, bound.ElseBody.Type))
{
throw new CompileException(expr.Position, String.Format(
"Branches of if/then/else do not return the same type. Then arm returns {0} while else arm returns {1}.",
bound.ThenBody.Type, bound.ElseBody.Type));
}
}
else
{
// no else, so make the then body doesn't return a value
if ((bound.ThenBody.Type != Decl.Unit) && (bound.ThenBody.Type != Decl.EarlyReturn))
{
throw new CompileException(expr.Position, String.Format(
"Body of if/then is returning type {0} but must be Unit (or a return) if there is no else branch.",
bound.ThenBody.Type));
}
}
return bound;
}
public virtual IUnboundExpr Transform(IfExpr expr)
{
return(expr);
}
IUnboundExpr IUnboundExprVisitor <IUnboundExpr> .Visit(IfExpr expr)
{
return(Call("IfExpr", Tuple(expr.Condition.Accept(this),
expr.ThenBody.Accept(this),
(expr.ElseBody != null) ? expr.ElseBody.Accept(this) : Call("UnitExpr", Unit()))));
}