(* Title: HOL/Examples/ML.thy
Author: Makarius
*)
section \<open>Isabelle/ML basics\<close>
theory "ML"
imports Main
begin
subsection \<open>ML expressions\<close>
text \<open>
The Isabelle command \<^theory_text>\<open>ML\<close> allows to embed Isabelle/ML source into the
formal text. It is type-checked, compiled, and run within that environment.
Note that side-effects should be avoided, unless the intention is to change
global parameters of the run-time environment (rare).
ML top-level bindings are managed within the theory context.
\<close>
ML \<open>1 + 1\<close>
ML \<open>val a = 1\<close>
ML \<open>val b = 1\<close>
ML \<open>val c = a + b\<close>
subsection \<open>Antiquotations\<close>
text \<open>
There are some language extensions (via antiquotations), as explained in the
``Isabelle/Isar implementation manual'', chapter 0.
\<close>
ML \<open>length []\<close>
ML \<open>\<^assert> (length [] = 0)\<close>
text \<open>Formal entities from the surrounding context may be referenced as
follows:\<close>
term "1 + 1" \<comment> \<open>term within theory source\<close>
ML \<open>\<^term>\<open>1 + 1\<close> (* term as symbolic ML datatype value *)\<close>
ML \<open>\<^term>\<open>1 + (1::int)\<close>\<close>
ML \<open>
(* formal source with position information *)
val s = \<open>1 + 1\<close>;
(* read term via old-style string interface *)
val t = Syntax.read_term \<^context> (Syntax.implode_input s);
\<close>
subsection \<open>Recursive ML evaluation\<close>
ML \<open>
ML \<open>ML \<open>val a = @{thm refl}\<close>\<close>;
ML \<open>val b = @{thm sym}\<close>;
val c = @{thm trans}
val thms = [a, b, c];
\<close>
subsection \<open>IDE support\<close>
text \<open>
ML embedded into the Isabelle environment is connected to the Prover IDE.
Poly/ML provides:
\<^item> precise positions for warnings / errors
\<^item> markup for defining positions of identifiers
\<^item> markup for inferred types of sub-expressions
\<^item> pretty-printing of ML values with markup
\<^item> completion of ML names
\<^item> source-level debugger
\<close>
ML \<open>fn i => fn list => length list + i\<close>
subsection \<open>Example: factorial and ackermann function in Isabelle/ML\<close>
ML \<open>
fun factorial 0 = 1
| factorial n = n * factorial (n - 1)
\<close>
ML \<open>factorial 42\<close>
ML \<open>factorial 10000 div factorial 9999\<close>
text \<open>See \<^url>\<open>http://mathworld.wolfram.com/AckermannFunction.html\<close>.\<close>
ML \<open>
fun ackermann 0 n = n + 1
| ackermann m 0 = ackermann (m - 1) 1
| ackermann m n = ackermann (m - 1) (ackermann m (n - 1))
\<close>
ML \<open>timeit (fn () => ackermann 3 10)\<close>
subsection \<open>Parallel Isabelle/ML\<close>
text \<open>
Future.fork/join/cancel manage parallel evaluation.
Note that within Isabelle theory documents, the top-level command boundary
may not be transgressed without special precautions. This is normally
managed by the system when performing parallel proof checking.
\<close>
ML \<open>
val x = Future.fork (fn () => ackermann 3 10);
val y = Future.fork (fn () => ackermann 3 10);
val z = Future.join x + Future.join y
\<close>
text \<open>
The \<^ML_structure>\<open>Par_List\<close> module provides high-level combinators for
parallel list operations.
\<close>
ML \<open>timeit (fn () => map (fn n => ackermann 3 n) (1 upto 10))\<close>
ML \<open>timeit (fn () => Par_List.map (fn n => ackermann 3 n) (1 upto 10))\<close>
subsection \<open>Function specifications in Isabelle/HOL\<close>
fun factorial :: "nat \ nat"
where
"factorial 0 = 1"
| "factorial (Suc n) = Suc n * factorial n"
term "factorial 4" \<comment> \<open>symbolic term\<close>
value "factorial 4" \<comment> \<open>evaluation via ML code generation in the background\<close>
declare [[ML_source_trace]]
ML \<open>\<^term>\<open>factorial 4\<close>\<close> \<comment> \<open>symbolic term in ML\<close>
ML \<open>@{code "factorial"}\<close> \<comment> \<open>ML code from function specification\<close>
fun ackermann :: "nat \ nat \ nat"
where
"ackermann 0 n = n + 1"
| "ackermann (Suc m) 0 = ackermann m 1"
| "ackermann (Suc m) (Suc n) = ackermann m (ackermann (Suc m) n)"
value "ackermann 3 5"
end
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