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diff --git a/sorsyl/lib/feature.ml b/sorsyl/lib/feature.ml
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+(** Module for handling phonological features and segments *)
+
+(* module Feature = struct *)
+
+(** Type representing a phonological feature value *)
+type feature_value = Plus | Minus | Zero
+
+(** Type representing a phonological feature *)
+type feature =
+  | Syllabic
+  | Sonorant
+  | Consonantal
+  | Continuant
+  | DelayedRelease
+  | Lateral
+  | Nasal
+  | Strident
+  | Voiced
+  | SpreadGlottis
+  | ConstrictedGlottis
+  | Anterior
+  | Coronal
+  | Distributed
+  | Labial
+  | High
+  | Low
+  | Back
+  | Rounded
+  | Velaric
+  | Tense
+  | Long
+  | HighTone
+  | HighReg (*high registry?*)
+
+type feature_spec = feature * feature_value
+(** Type representing a feature specification as a (value, feature) pair *)
+
+type segment = feature_spec list
+
+(** Convert a string feature value to the feature_value type *)
+let value_of_string = function
+  | "+" -> Plus
+  | "-" -> Minus
+  | "0" -> Zero
+  | s -> failwith (Printf.sprintf "Invalid feature value: %s" s)
+
+let string_of_feature = function
+  | "syl" -> Syllabic
+  | "son" -> Sonorant
+  | "cons" -> Consonantal
+  | "cont" -> Continuant
+  | "delrel" -> DelayedRelease
+  | "lat" -> Lateral
+  | "nas" -> Nasal
+  | "strid" -> Strident
+  | "voi" -> Voiced
+  | "sg" -> SpreadGlottis
+  | "cg" -> ConstrictedGlottis
+  | "ant" -> Anterior
+  | "cor" -> Coronal
+  | "distr" -> Distributed
+  | "lab" -> Labial
+  | "hi" -> High
+  | "lo" -> Low
+  | "back" -> Back
+  | "round" -> Rounded
+  | "velaric" -> Velaric
+  | "tense" -> Tense
+  | "long" -> Long
+  | "hitone" -> HighTone
+  | "hireg" -> HighReg
+  | _ -> failwith "not a valid feature"
+
+(** Check if a segment has a specific feature with a given value *)
+let has_feature (value, feature_name) segment =
+  List.exists (fun (v, f) -> v = value && f = feature_name) segment
+
+(** Create a feature test function for use in the decision tree *)
+let test feature_spec segment = has_feature feature_spec segment
+(* end *)