Complete 1.01.p.1

[tiger.ml.git] / exercises / ch01 / straight_line_program_interpreter.ml

diff --git a/exercises/ch01/straight_line_program_interpreter.ml b/exercises/ch01/straight_line_program_interpreter.ml
index e69de29..de4b921 100644 (file)
--- a/exercises/ch01/straight_line_program_interpreter.ml
+++ b/exercises/ch01/straight_line_program_interpreter.ml
@@ -0,0 +1,95 @@
+module List = ListLabels
+
+module Spl : sig
+  type id = string
+
+  type binop =
+    | Plus
+    | Minus
+    | Times
+    | Div
+
+  type stm =
+    | CompoundStm of stm * stm
+    | AssignStm of id * exp
+    | PrintStm of exp list
+  and exp =
+    | IdExp of id
+    | NumExp of int
+    | OpExp of exp * binop * exp
+    | EseqExp of stm * exp
+
+  val maxargs : stm -> int
+end = struct
+  type id = string
+
+  type binop =
+    | Plus
+    | Minus
+    | Times
+    | Div
+
+  type stm =
+    | CompoundStm of stm * stm
+    | AssignStm of id * exp
+    | PrintStm of exp list
+  and exp =
+    | IdExp of id
+    | NumExp of int
+    | OpExp of exp * binop * exp
+    | EseqExp of stm * exp
+
+    (* 01.p.1: Write ML function (maxargs : stm -> int) that tells the
+     * maximum number of arguments of any print statement within any
+     * subexpression of a given statement. For example, maxargs(prog)
+     * is 2.
+     *)
+    let maxargs stm =
+      let max = ref 0 in
+      let rec check_stm = function
+        | PrintStm exps ->
+            let exps_length = List.length exps in
+            if exps_length > !max then max := exps_length else ();
+            List.iter exps ~f:check_exp
+        | AssignStm (_, e) ->
+            check_exp e
+        | CompoundStm (s1, s2) ->
+            check_stm s1;
+            check_stm s2
+      and check_exp = function
+        | IdExp _ | NumExp _ -> ()
+        | OpExp (e1, _, e2) ->
+            check_exp e1;
+            check_exp e2
+        | EseqExp (s, e) ->
+            check_stm s;
+            check_exp e
+      in
+      check_stm stm;
+      !max
+end
+
+let spl_prog =
+  (*  a := 5 + 3;
+   *  b := (print(a, a - 1), 10 * a);
+   *  print(b)
+   *)
+  Spl.CompoundStm
+    ( Spl.AssignStm ("a", Spl.OpExp (Spl.NumExp 5, Spl.Plus, Spl.NumExp 3))
+    , Spl.CompoundStm
+        ( Spl.AssignStm
+          ( "b"
+          , Spl.EseqExp
+              ( Spl.PrintStm
+                  [ Spl.IdExp "a"
+                  ; Spl.OpExp (Spl.IdExp "a", Spl.Minus, Spl.NumExp 1)
+                  ]
+              , Spl.OpExp (Spl.NumExp 10, Spl.Times, Spl.IdExp "a")
+              )
+          )
+        , Spl.PrintStm [Spl.IdExp "b"]
+        )
+    )
+
+let () =
+  Printf.printf "maxargs: %d\n" (Spl.maxargs spl_prog)