Escape double curly braces in prompt template strings

lib/prompt/base.rb

@@ -66,6 +66,8 @@ def save(file_path:)
     # contained within the template. Input variables are defined as text enclosed in
     # curly braces (e.g. "{variable_name}").
     #
+    # Content within two consecutive curly braces (e.g. "{{ignore_me}}) are ignored.
+    #
     # @param template [String] The template string to extract variables from.
     #
     # @return [Array<String>] An array of input variable names.
@@ -74,9 +76,9 @@ def self.extract_variables_from_template(template)
       input_variables = []
       scanner = StringScanner.new(template)
 
-      while scanner.scan_until(/\{([^{}]*)\}/)
+      while scanner.scan_until(/\{([^}]*)\}/)
         variable = scanner[1].strip
-        input_variables << variable unless variable.empty?
+        input_variables << variable unless variable.empty? || variable[0] == "{"
       end
 
       input_variables

lib/prompt/prompt_template.rb

@@ -20,15 +20,15 @@ def initialize(template:, input_variables:, validate_template: true)
     end
 
     #
-    # Format the prompt with the inputs.
+    # Format the prompt with the inputs. Double {{}} replaced with single {} to adhere to f-string spec.
     #
     # @param kwargs [Hash] Any arguments to be passed to the prompt template.
     # @return [String] A formatted string.
     #
     def format(**kwargs)
       result = @template
       kwargs.each { |key, value| result = result.gsub(/\{#{key}\}/, value.to_s) }
-      result
+      result.gsub(/{{/, "{").gsub(/}}/, "}")
     end
 
     #

spec/prompts/base_spec.rb

@@ -34,4 +34,19 @@
       expect(File.directory?(non_existent_dir)).to be_truthy
     end
   end
+
+  describe "#extract_variables_from_template" do
+    let(:basic_template) { "Tell me a {adjective} joke." }
+    let(:escaped_template) { "Tell me a {adjective} joke. Return in JSON in the format {{joke: 'The joke'}}" }
+
+    it "extracts variables" do
+      input_variables = Prompt::Base.extract_variables_from_template(basic_template)
+      expect(input_variables).to eq(%w[adjective])
+    end
+
+    it "excludes double curly brace variables" do
+      input_variables = Prompt::Base.extract_variables_from_template(escaped_template)
+      expect(input_variables).to eq(%w[adjective])
+    end
+  end
 end