(* Title: HOL/ex/Computations.thy
Author: Florian Haftmann, TU Muenchen
*)
section \<open>Simple example for computations generated by the code generator\<close>
theory Computations
imports "../Nat" "../Fun_Def" "../Num" "../Code_Numeral"
begin
fun even :: "nat \<Rightarrow> bool"
where "even 0 \<longleftrightarrow> True"
| "even (Suc 0) \<longleftrightarrow> False"
| "even (Suc (Suc n)) \<longleftrightarrow> even n"
fun fib :: "nat \<Rightarrow> nat"
where "fib 0 = 0"
| "fib (Suc 0) = Suc 0"
| "fib (Suc (Suc n)) = fib (Suc n) + fib n"
declare [[ML_source_trace]]
ML \<open>
local
fun int_of_nat @{code "0 :: nat"} = 0
| int_of_nat (@{code Suc} n) = int_of_nat n + 1;
in
val comp_nat = @{computation "0 :: nat" Suc
"plus :: nat \<Rightarrow>_" "times :: nat \<Rightarrow> _" fib :: nat}
(fn post => post o HOLogic.mk_nat o int_of_nat);
val comp_numeral = @{computation "0 :: nat" "1 :: nat" "2 :: nat" "3 :: nat" :: nat}
(fn post => post o HOLogic.mk_nat o int_of_nat);
val comp_bool = @{computation True False HOL.conj HOL.disj HOL.implies
HOL.iff even "less_eq :: nat \<Rightarrow> _" "less :: nat \<Rightarrow> _" "HOL.eq :: nat \<Rightarrow> _" :: bool }
(K I);
end
\<close>
declare [[ML_source_trace = false]]
ML_val \<open>
comp_nat @{context} @{term "fib (Suc (Suc (Suc 0)) * Suc (Suc (Suc 0))) + Suc 0"}
|> Syntax.string_of_term @{context}
|> writeln
\<close>
ML_val \<open>
comp_bool @{context} @{term "fib (Suc (Suc (Suc 0)) * Suc (Suc (Suc 0))) + Suc 0 < fib (Suc (Suc 0))"}
\<close>
ML_val \<open>
comp_numeral @{context} @{term "Suc 42 + 7"}
|> Syntax.string_of_term @{context}
|> writeln
\<close>
end