Theoretical physicist turned software engineer, passionate for functional programming, functional type theory, and declarative domain-specific languages - winitzki

private[ch] def leftUnify(src: TypeExpr, dst: TypeExpr, fullSrc: TypeExpr): UnifyResult = {
   // Check whether some type variables are not mapped but used in other variables' maps.
   // In this case, we need to auto-rename them.
   leftUnifyRec(src, dst, Map()).right.map { substitutions =>
     val usedVars = substitutions.values.map(allTypeParams).foldLeft(Set[TP]())(_ ++ _)
     val unmappedVars = (usedVars intersect allTypeParams(fullSrc)) -- substitutions.keySet
     val alphaConversions: Map[TP, TypeExpr] = unmappedVars.toSeq.map {
       _ → TP(freshTypeVarIdents())
     }(scala.collection.breakOut)
     substitutions ++ alphaConversions
   }
 }