1 files changed, 23 insertions, 4 deletions
diff --git a/lib/coq/Sail2_string.v b/lib/coq/Sail2_string.v
index 8bd7f0a6..9ca9cb67 100644
--- a/lib/coq/Sail2_string.v
+++ b/lib/coq/Sail2_string.v
@@ -7,10 +7,29 @@ Definition string_startswith s expected :=
   let prefix := String.substring 0 (String.length expected) s in
   generic_eq prefix expected.
 
-Definition string_drop s n :=
-  let n := Z.to_nat n in
+Definition string_drop s (n : {n : Z & ArithFact (n >= 0)}) :=
+  let n := Z.to_nat (projT1 n) in
   String.substring n (String.length s - n) s.
 
-Definition string_length s := Z.of_nat (String.length s).
+Definition string_length s : {n : Z & ArithFact (n >= 0)} :=
+ build_ex (Z.of_nat (String.length s)).
 
-Definition string_append := String.append.
-\ No newline at end of file
+Definition string_append := String.append.
+
+(* TODO: maybe_int_of_prefix, maybe_int_of_string *)
+
+Fixpoint n_leading_spaces (s:string) : nat :=
+  match s with
+  | EmptyString => 0
+  | String " " t => S (n_leading_spaces t)
+  | _ => 0
+  end.
+
+Definition opt_spc_matches_prefix s : option (unit * {n : Z & ArithFact (n >= 0)}) :=
+  Some (tt, build_ex (Z.of_nat (n_leading_spaces s))).
+
+Definition spc_matches_prefix s : option (unit * {n : Z & ArithFact (n >= 0)}) :=
+  match n_leading_spaces s with
+  | O => None
+  | S n => Some (tt, build_ex (Z.of_nat (S n)))
+  end.
+\ No newline at end of file