wyil.checks

Class CoercionCheck

java.lang.Object

wyil.checks.CoercionCheck

All Implemented Interfaces:

wybs.lang.Build.Stage<WyilFile>, wycc.lang.Feature

public class CoercionCheck
extends Object
implements wybs.lang.Build.Stage<WyilFile>

The point of the coercion check is to check that all convert bytecodes make sense, and are not ambiguous. For example, consider the following code:

 define Rec1 as { real x, int y }
 define Rec2 as { int x, real y }
 define uRec1Rec2 as Rec1 | Rec2

 int f(uRec1Rec2 r):
  if r is Rec1:
      return r.y
  else:
      return r.x

 int g():
  rec = { x: 1, y: 1}
  return f(rec)
 

An implicit coercion will be inserted just before the last statement in g(). This will be:

 convert {int x,int y} => {real x,int y}|{int x,real y}
 

However, this conversion is ambiguous because we could convert the left-hand side to either of the two options in the right-hand side.

Author:

David J. Pearce

Nested Class Summary

Nested classes/interfaces inherited from interface wycc.lang.Feature

wycc.lang.Feature.Configurable, wycc.lang.Feature.ConfigurationError

Constructor Summary

Constructors

Constructor and Description
CoercionCheck(wybs.lang.Build.Task builder)

Method Summary

Modifier and Type	Method and Description
void	apply(WyilFile module)
protected void	check(SyntaxTree tree)
protected void	check(Type from, Type to, HashSet<wycc.util.Pair<Type,Type>> visited, wybs.lang.SyntacticElement element) Recursively check that there is no ambiguity in coercing type from into type to.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CoercionCheck

public CoercionCheck(wybs.lang.Build.Task builder)

Method Detail

apply

public void apply(WyilFile module)

Specified by:

apply in interface wybs.lang.Build.Stage<WyilFile>

check

protected void check(SyntaxTree tree)

check

protected void check(Type from,
                     Type to,
                     HashSet<wycc.util.Pair<Type,Type>> visited,
                     wybs.lang.SyntacticElement element)
              throws wybs.util.ResolveError

Recursively check that there is no ambiguity in coercing type from into type to. The visited set is necessary to ensure this process terminates in the presence of recursive types.

Parameters:

from -

to -

visited - - the set of pairs already checked.

location - - source location attribute (if applicable).

Throws:

wybs.util.ResolveError - If a named type within this condition cannot be resolved within the enclosing project.