1 files changed, 97 insertions, 0 deletions
diff --git a/lib/lexing/lexer.ml b/lib/lexing/lexer.ml
new file mode 100644
index 0000000..af24e49
--- /dev/null
+++ b/lib/lexing/lexer.ml
@@ -0,0 +1,97 @@
+(* Lexer for transforming an input string into a list of tokens *)
+
+open Types
+open Headers
+open Utils
+
+(*
+  Ordered lexer rules:
+
+  true            => TRUE         [1,2,3,4]
+  false           => FALSE        [5,6,7,8,9]
+  [a-zA-Z]+ as s  => LIT s        [10]
+  ¬               => NOT          [11]
+  ∧               => AND          [12]
+  ∨               => OR           [13]
+  →               => IMPLIES      [14]
+  ↔               => IFF          [15]
+  (               => LEFT_PAREN   [16]
+  )               => RIGHT_PAREN  [17]
+  [ \t\n]         => SKIP         [18]
+*)
+
+(* Define a TDFA *)
+let my_tdfa : tdfa =
+  let my_alphabet =
+    let lowercase = List.init 26 (fun i -> Char.chr (Char.code 'a' + i)) in
+    let uppercase = List.init 26 (fun i -> Char.chr (Char.code 'A' + i)) in
+    ['!'; '&'; '|'; '>'; '='; '('; ')'; ' '; '\t'; '\n'] @ lowercase @ uppercase
+  in
+
+  let my_delta (i, c) =
+    if
+      not (List.mem c my_alphabet)
+    then
+      raise (Not_In_Alphabet c)
+    else
+      let append_lit = function
+          | LIT s -> LIT (s ^ Char.escaped c)
+          | _ -> LIT (Char.escaped c)
+      in
+
+      let is_ltr c =
+        let ascii = Char.code c in
+        (65 <= ascii && ascii <= 90) || (97 <= ascii && ascii <= 122)
+      in
+
+      match i, c with
+      | 0, '!'                  -> 11, (fun _ -> NOT)
+      | 0, '&'                  -> 12, (fun _ -> AND)
+      | 0, '|'                  -> 13, (fun _ -> OR)
+      | 0, '>'                  -> 14, (fun _ -> IMPLIES)
+      | 0, '='                  -> 15, (fun _ -> IFF)
+      | 0, '('                  -> 16, (fun _ -> LEFT_PAREN)
+      | 0, ')'                  -> 17, (fun _ -> RIGHT_PAREN)
+      | 0, ' '                  -> 18, (fun _ -> SKIP)
+      | 0, '\t'                 -> 18, (fun _ -> SKIP)
+      | 0, '\n'                 -> 18, (fun _ -> SKIP)
+      | 0, 't'                  -> 1, append_lit
+      | 0, 'f'                  -> 5, append_lit
+      | 0, c when is_ltr c      -> 10, append_lit
+      | 1, 'r'                  -> 2, append_lit
+      | 1, c when is_ltr c      -> 10, append_lit
+      | 2, 'u'                  -> 3, append_lit
+      | 2, c when is_ltr c      -> 10, append_lit
+      | 3, 'e'                  -> 4, (fun _ -> TRUE)
+      | 3, c when is_ltr c      -> 10, append_lit
+      | 4, c when is_ltr c      -> 10, (fun _ -> (LIT ("true" ^ Char.escaped c)))
+      | 5, 'a'                  -> 6, append_lit
+      | 5, c when is_ltr c      -> 10, append_lit
+      | 6, 'l'                  -> 7, append_lit
+      | 6, c when is_ltr c      -> 10, append_lit
+      | 7, 's'                  -> 8, append_lit
+      | 7, c when is_ltr c      -> 10, append_lit
+      | 8, 'e'                  -> 9, (fun _ -> FALSE)
+      | 8, c when is_ltr c      -> 10, append_lit
+      | 9, c when is_ltr c      -> 10, (fun _ -> (LIT ("false" ^ Char.escaped c)))
+      | 10, c when is_ltr c     -> 10, append_lit
+      | _                       -> raise (No_Transition (i, c))
+  in
+
+  {
+    alphabet = my_alphabet;
+    start_state = 0;
+    register_init = SKIP;
+    delta = my_delta
+  }
+
+
+let lex (s : string) : tok list =
+  let to_parse = s |> String.to_seq |> List.of_seq in
+  let initial_tdfa_state = {
+    state_id = my_tdfa.start_state;
+    register = my_tdfa.register_init;
+    tokens = [];
+    to_parse = to_parse
+  } in
+  driver my_tdfa initial_tdfa_state