first commit

eval.cpp

@@ -0,0 +1,129 @@
+#include "expr.hpp"
+
+struct EvalVisitor : Visitor {
+
+    static const uint32_t max_depth = 32;
+
+    bool fail;
+    uint32_t depth;
+    double stack[max_depth];
+
+    EvalVisitor()
+    {
+        depth = 0;
+        fail = false;
+    }
+
+    void visit_int(IntValue *node)
+    {
+        if (fail) return;
+
+        if (depth == max_depth) {
+            fail = true;
+            return;
+        }
+
+        stack[depth++] = node->val;
+    }
+
+    void visit_float(FloatValue *node)
+    {
+        if (fail) return;
+
+        if (depth == max_depth) {
+            fail = true;
+            return;
+        }
+
+        stack[depth++] = node->val;
+    }
+
+    void visit_neg(NegOperation *node)
+    {
+        node->op->visit(*this);
+        
+        if (fail) return;
+
+        if (depth < 1) {
+            fail = true;
+            return;
+        }
+        
+        stack[depth-1] = -stack[depth-1];
+    }
+
+    void visit_add(AddOperation *node)
+    {
+        node->lhs->visit(*this);
+        node->rhs->visit(*this);
+
+        if (fail) return;
+
+        if (depth < 2) {
+            fail = true;
+            return;
+        }
+        
+        double rhs = stack[--depth];
+        double lhs = stack[--depth];
+        stack[depth++] = lhs + rhs;
+    }
+
+    void visit_sub(SubOperation *node)
+    {
+        node->lhs->visit(*this);
+        node->rhs->visit(*this);
+
+        if (fail) return;
+
+        if (depth < 2) {
+            fail = true;
+            return;
+        }
+        
+        double rhs = stack[--depth];
+        double lhs = stack[--depth];
+        stack[depth++] = lhs - rhs;
+    }
+
+    void visit_mul(MulOperation *node)
+    {
+        node->lhs->visit(*this);
+        node->rhs->visit(*this);
+
+        if (fail) return;
+
+        if (depth < 2) {
+            fail = true;
+            return;
+        }
+        
+        double rhs = stack[--depth];
+        double lhs = stack[--depth];
+        stack[depth++] = lhs * rhs;
+    }
+
+    void visit_div(DivOperation *node)
+    {
+        node->lhs->visit(*this);
+        node->rhs->visit(*this);
+
+        if (fail) return;
+
+        if (depth < 2) {
+            fail = true;
+            return;
+        }
+        
+        double rhs = stack[--depth];
+        double lhs = stack[--depth];
+        stack[depth++] = lhs / rhs;
+    }
+};
+
+double eval(Expr *e)
+{
+    EvalVisitor visitor;
+    e->visit(visitor);
+    return visitor.stack[visitor.depth-1];
+}