Starting with the lexer, i'm starting to comprehend better what pratt parsing is and how to apply it. For now just declaring basic structure and functions

src/lexer.c

@@ -141,7 +141,7 @@ LexerErr tokenize(const char *input, ASTNodeArray *out) {
             }
             ASTNode new_node = {
                 .type = NODE_BINARY_OP,
-                .data.binary.op = current,
+                .data.binary.op = char_to_operator(current),
                 .data.binary.right = NULL,
                 .data.binary.left = NULL,
             };
@@ -158,6 +158,10 @@ LexerErr tokenize(const char *input, ASTNodeArray *out) {
         offset++;
     }
 
+    if (arr.len < 1) {
+        return LEXER_EMPTY_INPUT;
+    }
+
     *out = arr;
     return LEXER_OK;
 }
@@ -225,3 +229,22 @@ bool isoperator(int c) {
             return false;
     }
 }
+
+Operator char_to_operator(int c) {
+    switch (c) {
+        case '+':
+            return OP_ADD;
+            break;
+        case '-':
+            return OP_SUB;
+            break;
+        case '*':
+            return OP_MUL;
+            break;
+        case '/':
+            return OP_DIV;
+            break;
+        default: // I mean shouldn't be used, we assume
+            return -1;
+    }
+}