Adding some sample code for a LL1-Parser to build an abstract syntax tree.

1 files changed, 61 insertions, 0 deletions

diff --git a/other/parser.cpp b/other/parser.cpp
new file mode 100644
index 0000000..94b7829
--- /dev/null
+++ b/other/parser.cpp
@@ -0,0 +1,61 @@
+struct Token { // In globalem Vektor, Zugriff über globale Variable.
+  int type; // Definiere Konstanten.
+  double value;
+  Token(int type) : type(type) {}
+  Token(int type, int value) : type(type), value(value) {}
+};
+
+struct Expression { // Die folgenden Klassen nur für den AST.
+  virtual ~Expression() {};
+  virtual double getValue() = 0;
+};
+
+struct Atom : public Expression {
+  double value;
+  Atom(int value) : value(value) {};
+  double getValue() { return value; }
+};
+
+struct BinaryExpression : public Expression {
+  Expression *lhs, *rhs;
+  BinaryExpression(Expression *lhs, Expression *rhs) : lhs(lhs), rhs(rhs) {}
+  ~BinaryExpression() { delete lhs; delete rhs; }
+};
+
+struct Addition : public BinaryExpression {
+  Addition(Expression *lhs, Expression *rhs) : BinaryExpression(lhs, rhs) {}
+  double getValue() { return lhs->getValue() + rhs->getValue(); }
+};
+
+Expression* parseF() {
+  Expression *lhs;
+  switch(tokens[token].type) {
+    case NUMBER: return new Atom(tokens[token++].value);
+    case LEFT_PAR:
+      token++;
+      lhs = parseA();
+      token++;
+      return lhs;
+    default:
+      return NULL;
+}}
+
+Expression* parseA_(Expression *lhs) {
+  Expression *plus, *minus;
+  if (token >= (int)tokens.size()) return lhs;
+  switch(tokens[token].type) {
+    case ADDITION:
+      token++;
+      plus = new Addition(lhs, parseS());
+      return parseA_(plus);
+    case SUBTRACTION:
+      token++;
+      minus = new Subtraction(lhs, parseS());
+      return parseA_(minus);
+    default:
+      return lhs;
+}}
+
+Expression* parseA() {
+  Expression *lhs = parseS(); return parseA_(lhs);
+}