Fix prompt generation

evoprompt/task/base_prompts_mixin.py

@@ -37,7 +37,7 @@ class BasePromptsFromGeneration:
         self.validation_dataset: Dataset
         samples = self.validation_dataset._select_contiguous(0, 5)
         prompt = "I gave a friend an instruction and five inputs. The friend read the instruction and wrote an output for every one of the inputs. Here are the input-output pairs:\n"
-        prompt += self.build_demonstration_prompt(samples, prompt=prompt)
+        prompt = self.build_demonstration_prompt(samples, prompt=prompt)
         prompt += "\nThe instruction was "
 
         generated_prompts = []