feat: add conditionals

1 files changed, 54 insertions, 4 deletions

diff --git a/eval.c b/eval.c
index 8c92cd8..eddeb6b 100644
--- a/eval.c
+++ b/eval.c
@@ -1,11 +1,13 @@
 #include <assert.h>
 #include <inttypes.h>
+#include <stdbool.h>
 #include <stdio.h>
 
 #include "eval.h"
 
 static int evaluate_type(const struct Node* node, struct Type* out);
 static int evaluate_value(const struct Node* node, int64_t* out);
+static int evaluate_condition(const struct Node* node, bool* out);
 
 static int complain(const struct Node* node, const char* message)
 {
@@ -26,6 +28,7 @@ static int evaluate_value(const struct Node* node, int64_t* out)
     int64_t left = 0;
     int64_t right = 0;
     struct Type type;
+    bool truth = false;
     switch (node->kind)
     {
         case VALUE_DIFFERENCE:
@@ -56,11 +59,14 @@ static int evaluate_value(const struct Node* node, int64_t* out)
         case VALUE_TUPLE_SIZE:
             if (evaluate_type(node->first, &type))
                 return 1;
-
-            // a non-array has no extent, so it gets zero, exactly like the real thing
             *out = type.kind == KIND_ARRAY ? type.number : 0;
             return 0;
         case VALUE_INTEGRAL_CONSTANT: return evaluate_value(node->first, out);
+        case VALUE_CONDITIONAL:
+            if (evaluate_condition(node->first, &truth))
+                return 1;
+
+            return evaluate_value(truth ? node->second : node->third, out);
         default: break;
     }
 
@@ -73,6 +79,7 @@ static int evaluate_type(const struct Node* node, struct Type* out)
     out->kind = KIND_VOID;
     out->number = 0;
     struct Type element;
+    bool truth = false;
     switch (node->kind)
     {
         case TYPE_VOID: return 0;
@@ -81,12 +88,14 @@ static int evaluate_type(const struct Node* node, struct Type* out)
         case TYPE_SIZE: out->kind = KIND_SIZE; return 0;
         case TYPE_REMOVE_CV: return evaluate_type(node->first, out);
         case TYPE_ARRAY:
-            // the element type is evaluated for its side of the bargain, then forgotten
             if (evaluate_type(node->first, &element) || evaluate_value(node->second, &out->number))
                 return 1;
-
             out->kind = KIND_ARRAY;
             return 0;
+        case TYPE_CONDITIONAL:
+            if (evaluate_condition(node->first, &truth))
+                return 1;
+            return evaluate_type(truth ? node->second : node->third, out);
         case TYPE_DECLTYPE:
             if (evaluate_value(node->first, &out->number))
                 return 1;
@@ -99,6 +108,47 @@ static int evaluate_type(const struct Node* node, struct Type* out)
     return 1;
 }
 
+static bool same_type(const struct Type* left, const struct Type* right)
+{
+    return left->kind == right->kind && left->number == right->number;
+}
+
+static int evaluate_condition(const struct Node* node, bool* out)
+{
+    int64_t left = 0;
+    int64_t right = 0;
+    struct Type left_type;
+    struct Type right_type;
+    *out = false;
+    switch (node->kind)
+    {
+        case COND_TRUE: *out = true; return 0;
+        case COND_FALSE: return 0;
+        case COND_IS_SAME:
+            if (evaluate_type(node->first, &left_type) || evaluate_type(node->second, &right_type))
+                return 1;
+
+            *out = same_type(&left_type, &right_type);
+            return 0;
+        case COND_EQUAL:
+            if (evaluate_operands(node, &left, &right))
+                return 1;
+
+            *out = left == right;
+            return 0;
+        case COND_LESS:
+            if (evaluate_operands(node, &left, &right))
+                return 1;
+
+            *out = left < right;
+            return 0;
+        default: break;
+    }
+
+    assert(!"the parser handed a non-condition where a condition goes");
+    return 1;
+}
+
 static enum RunStatus emit(const struct Node* node)
 {
     struct Type type;