added a functional parser

1 files changed, 36 insertions, 0 deletions

diff --git a/lib/lexing/utils.ml b/lib/lexing/utils.ml
new file mode 100644
index 0000000..aa218f5
--- /dev/null
+++ b/lib/lexing/utils.ml
@@ -0,0 +1,36 @@
+open Types
+open Headers
+
+(* Function for stepping through a TDFA computation *)
+let step (automaton : tdfa) (state : tdfa_state) : tdfa_state =
+  match state.to_parse with
+  | [] -> state
+  | c :: cs ->
+    try
+      let next_state_id, f = automaton.delta (state.state_id, c) in
+      let next_tok = f state.register in
+      {
+        state_id = next_state_id;
+        register = next_tok;
+        tokens = state.tokens;
+        to_parse = cs
+      }
+    with (No_Transition (_, c)) ->
+      let token_to_add = state.register in
+      let next_state_id, f = automaton.delta (0, c) in
+      let next_tok = f SKIP in
+      {
+        state_id = next_state_id;
+        register = next_tok;
+        tokens = if token_to_add <> SKIP then token_to_add :: state.tokens else state.tokens;
+        to_parse = cs
+      }
+
+(* Driver to perform a TDFA computation *)
+let rec driver (automaton : tdfa) (state: tdfa_state) : tok list =
+  if
+    state.to_parse = []
+  then
+    List.rev (state.register :: state.tokens) (* ensure that final tag is emitted *)
+  else
+    driver automaton (step automaton state)