// Flatten out all expressions with a given head.
void Expression::Flatten(const string head)
{
ExprVector newLeaves;
newLeaves.reserve(leaves.size());
for(ExprVector::const_iterator leaf = leaves.begin(); leaf != leaves.end(); ++leaf)
if((*leaf)->FunctionName() == head)
{
for(ExprVector::const_iterator subLeaf = (*leaf)->Leaves().begin(); subLeaf != (*leaf)->Leaves().end(); ++subLeaf)
newLeaves.push_back(*subLeaf);
(*leaf)->Leaves().clear();
delete *leaf;
}
else
newLeaves.push_back(*leaf);
leaves = newLeaves;
}
// Evaluates an expression. Considers all rules etc. In some cases there are simply
// no changes possible and the expression remains unchanged (e.g. a+b).
void Expression::Evaluate(Calculator *calculator, int32 recursions)
{
// Since the expression is expected to be already structured, it must have a head.
if(!head)
throw DefinitionException("Expression::Evaluate: Expression has no head.");
if(recursions > Max_Evaluate_Recursions)
throw LimitationException("Maximum number of recursive definitions reached.");
head->Evaluate(calculator, recursions);
// If Expression is a symbol
Definition *symbolDef = SymbolDefinition(calculator);
if(symbolDef)
{
// Look if value is defined
if(symbolDef->Value())
{
bool changed = !SameExpression(symbolDef->Value());
AssignCloned(symbolDef->Value());
if(changed)
Evaluate(calculator, recursions + 1);
}
}
// If head is a pure function
if(head->FunctionName() == "Function" && head->LeafCount() == 1)
{
ExprPtr body(head->leaves.at(0));
body->SubstituteSlots(leaves);
body->Evaluate(calculator, recursions);
head->leaves.clear();
MoveNotCloned(body);
}
// If Expression is Function call
Definition *def = FunctionDefinition(calculator);
if(def)
{
AttributeSet attributes = def->Attributes();
// Evaluate child leaves if no Hold attribute
if(!attributes.Contains(atHoldAll) && !attributes.Contains(atHoldAllComplete))
{
if(!attributes.Contains(atHoldFirst))
if(!leaves.empty())
leaves.at(0)->Evaluate(calculator, recursions);
if(!attributes.Contains(atHoldRest))
if(leaves.size() > 1)
for(ExprVector::const_iterator leaf = leaves.begin()+1; leaf != leaves.end(); ++leaf)
(*leaf)->Evaluate(calculator, recursions);
}
// Flatten out sequences
if(!attributes.Contains(atSequenceHold))
{
Flatten("Sequence");
}
// Apply down values
for(ExprVector::const_iterator leaf = leaves.begin(); leaf != leaves.end(); ++leaf)
{
Definition *def(0);
if((*leaf)->SymbolHead())
def = (*leaf)->SymbolDefinition(calculator);
else if((*leaf)->IsFunctionCall())
def = (*leaf)->FrontFunctionDefinition(calculator);
if(def)
{
bool changed(false);
if(def->ApplyUpValues(this, calculator, &changed) && changed)
{
Evaluate(calculator, recursions + 1);
return;
}
}
}
// Apply Flat attribute
if(attributes.Contains(atFlat))
{
Flatten(FunctionName());
}
// Apply OneIdentity attribute
if(attributes.Contains(atOneIdentity))
{
if(ApplyOneIdentity())
return;
}
// Apply Listable attribute
if(attributes.Contains(atListable))
{
// Determine resulting list length, check if there are lists with different lengths
bool listFound(false);
ExprVector::size_type listSize(0);
for(ExprVector::const_iterator leaf = leaves.begin(); leaf != leaves.end(); ++leaf)
if((*leaf)->FunctionName() == "List")
if(!listFound)
{
listSize = (*leaf)->LeafCount();
listFound = true;
}
else
if(listSize != (*leaf)->LeafCount())
throw EvaluateException("Listable operation requires lists of the same length.");
// Construct resulting list
if(listFound)
{
ExprVector items;
// Number of resulting list items = items in operand list
items.reserve(listSize);
// Loop through list items
for(ExprVector::size_type position = 0; position < listSize; ++position)
{
// List item = function call, number of operands = number of original operands
Expression *item = new Expression(FunctionName(), leaves.size());
for(ExprVector::iterator itemLeaf = leaves.begin(); itemLeaf != leaves.end(); ++itemLeaf)
{
if((*itemLeaf)->FunctionName() == "List")
{
// Add corresponding list item
item->AppendLeaf(*((*itemLeaf)->leaves.begin() + position));
}
else
{
// Add "whole" item (clone if necessary)
if(position == 0)
item->AppendLeaf(*itemLeaf);
else
item->AppendLeaf((*itemLeaf)->Clone());
}
}
items.push_back(item);
}
// Delete lists (elements are now in resulting list)
for(ExprVector::iterator itemLeaf = leaves.begin(); itemLeaf != leaves.end(); ++itemLeaf)
if((*itemLeaf)->FunctionName() == "List")
{
(*itemLeaf)->leaves.clear();
delete *itemLeaf;
}
delete head;
head = new Expression("List");
leaves = items;
// Evaluate the list for itself
Evaluate(calculator, recursions);
return;
}
}
// Apply Orderless attribute
if(attributes.Contains(atOrderless))
{
std::sort(leaves.begin(), leaves.end(), &Compare);
}
// Apply down value rules
bool changed(false);
if(def->ApplyDownValues(this, calculator, &changed))
{
if(changed)
Evaluate(calculator, recursions + 1);
return;
}
// Execute linked operator, if specified
if(def->Predef())
def->Predef()->Apply(this, calculator, recursions);
}
else
{
// Otherwise simply evaluate the leaves
for(ExprVector::const_iterator leaf = leaves.begin(); leaf != leaves.end(); ++leaf)
(*leaf)->Evaluate(calculator, recursions);
}
}