[sml] regex match using cps

coq/README.org

@@ -1,8 +1,8 @@
 #+TITLE: Coq
 
- - [[./sumn.v]]: Sum of first n natural numbers, their squares and cubes.
- - [[./de-morgan.v]]: de-Morgan's laws
- - [[./eqns.v]]: A 'hello world' using the 'equations' plugin
- - [[./cpdt/]]: stuff from the book CPDT
- - [[./sf/]]: stuff from /Software foundations/
+ - [[./sumn.v][sumn.v]]: Sum of first n natural numbers, their squares and cubes.
+ - [[./de-morgan.v][de-morgan.v]]: de-Morgan's laws
+ - [[./eqns.v][eqns.v]]: A 'hello world' using the 'equations' plugin
+ - [[./cpdt/][cpdt/]]: stuff from the book CPDT
+ - [[./sf/][sf]]: stuff from /Software foundations/
 

lua/README.org

@@ -1,14 +1,14 @@
 #+TITLE: Lua
 Most code snippets are from 2018..
 
- - [[./calc.lua]]: Basic calculator
- - [[./gambler_ruin.lua]]: Gambler's ruin problem
- - [[./quadraticEqn.lua]]: Solving a quadratic equation
- - [[./co-routine.lua]]: Coroutines
- - [[./lua]]-dice.lua: Random number generation
- - [[./producer_consumer.lua]]: Producer consumer problem
- - [[./tables.lua]]: Using tables
- - [[./rev_table.lua]]: Reverse a table
+ - [[./calc.lua][calc.lua]]: Basic calculator
+ - [[./gambler_ruin.lua][gambler_ruin.lua]]: Gambler's ruin problem
+ - [[./quadraticEqn.lua][quadraticEqn.lua]]: Solving a quadratic equation
+ - [[./co-routine.lua][co-routine.lua]]: Coroutines
+ - [[./lua][lua]]-dice.lua: Random number generation
+ - [[./producer_consumer.lua][producer_consumer.lua]]: Producer consumer problem
+ - [[./tables.lua][tables.lua]]: Using tables
+ - [[./rev_table.lua][rev_table.lua]]: Reverse a table
 
  #- [[./tail_call_debate.lua]]
  #- [[./sinlua]].lua

sml/re-cps.sml

@@ -0,0 +1,54 @@
+(* Starting with int regex *)
+datatype re
+  = Null
+  | Eps
+  | Chr of int
+  | Cat of re * re
+  | Alt of re * re
+  | Star of re
+
+fun op /\ (x, y) = Cat (x, y)
+fun op \/ (x, y) = Alt (x, y)
+infixr 8 /\
+infixr 9 \/
+       
+(* checker : re -> (int list -> bool) -> (int list -> bool) *)
+fun compile r k l =
+  case r of
+    Null => false
+  | Eps => k l
+  | Chr c =>
+      (case l of
+        [] => false
+      | x::xs => if x=c then k xs
+		 else k (x::xs))
+  | Cat (r1, r2) => compile r1
+      (fn xs => compile r2 k xs) l
+  | Alt (r1, r2) => compile r1 k l orelse compile r2 k l
+  | Star rr => (compile Eps k l) orelse compile (Cat (r, Star rr)) k l
+(*
+- compile (Chr 3) (fn l => fn b => if l=nil then b else false) [3];
+val it = true : bool
+- compile (Chr 3) (fn l => fn b => if l=nil then b else false) [2];
+val it = false : bool
+*)
+	     
+(* matcher : re -> (int list -> bool) *)
+fun matcher r l = compile r
+  (fn l => if l=nil then true else false) l
+(*
+- matcher ((Chr 1) /\ (Chr 2)) [1];
+val it = false : bool
+- matcher ((Chr 1) /\ (Chr 2)) [1,2];
+val it = true : bool
+- matcher ((Chr 1) /\ (Chr 2)) [1,2,3];
+val it = false : bool
+*)
+
+(*
+Goes into an infinite loop when [Star] is involved.
+
+Puzzles me..
+
+See: https://www.cs.cmu.edu/~rwh/papers/regexp/jfp.pdf
+*)