prompt: support nested json data in #format

Close: #745

lib/langchain/prompt/prompt_template.rb

@@ -58,8 +58,9 @@ def initialize(template:, input_variables:, validate_template: true)
     #
     def format(**kwargs)
       result = @template
-      kwargs.each { |key, value| result = result.gsub(/\{#{key}\}/, value.to_s) }
       result.gsub(/{{/, "{").gsub(/}}/, "}")
+      kwargs.each { |key, value| result = result.gsub(/\{#{key}\}/, value.to_s) }
+      result
     end
 
     #

spec/langchain/prompts/prompt_template_spec.rb

@@ -64,6 +64,17 @@
 
       expect(prompt.format(adjective: "funny", content: "chickens")).to eq("Tell me a funny joke about chickens.")
     end
+
+    it "handles nested JSON data correctly" do
+      schema = '{"nested":{"foo":"bar"}}'
+
+      prompt = described_class.new(
+        template: "This is a JSON schema: {schema}",
+        input_variables: ["schema"]
+      )
+
+      expect(prompt.format(schema: schema)).to eq("This is a JSON schema: #{schema}")
+    end
   end
 
   describe "#from_template" do