From 4f21c45748816c9e0cd4f93fa6f6d167e9757f81 Mon Sep 17 00:00:00 2001
From: Matej Kosik
Date: Tue, 30 Aug 2016 11:47:35 +0200
Subject: CLEANUP: switching from "right-to-left" to "left-to-right" function
 composition operator.

Short story:

    This pull-request:

    (1) removes the definition of the "right-to-left" function composition operator

    (2) adds the definition of the "left-to-right" function composition operator

    (3) rewrites the code relying on "right-to-left" function composition to rely on "left-to-right" function composition operator instead.

Long story:

    In mathematics, function composition is traditionally denoted with ∘ operator.

    Ocaml standard library does not provide analogous operator under any name.

    Batteries Included provides provides two alternatives:

    	_ % _

    and

    	_ %> _

    The first operator one corresponds to the classical ∘ operator routinely used in mathematics.
    I.e.:

    	(f4 % f3 % f2 % f1) x  ≜  (f4 ∘ f3 ∘ f2 ∘ f1) x

    We can call it "right-to-left" composition because:
    - the function we write as first (f4) will be called as last
    - and the function write as last (f1) will be called as first.

    The meaning of the second operator is this:

    	(f1 %> f2 %> f3 %> f4) x  ≜  (f4 ∘ f3 ∘ f2 ∘ f1) x

    We can call it "left-to-right" composition because:
    - the function we write as first (f1) will be called first
    - and the function we write as last (f4) will be called last
    That is, the functions are written in the same order in which we write and read them.

    I think that it makes sense to prefer the "left-to-right" variant because
    it enables us to write functions in the same order in which they will be actually called
    and it thus better fits our culture
    (we read/write from left to right).
---
 engine/evd.ml | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

(limited to 'engine')

diff --git a/engine/evd.ml b/engine/evd.ml
index 3aab39eda1..913856a8da 100644
--- a/engine/evd.ml
+++ b/engine/evd.ml
@@ -246,7 +246,7 @@ let evar_instance_array test_id info args =
     instrec filter (evar_context info) 0
 
 let make_evar_instance_array info args =
-  evar_instance_array (isVarId % NamedDecl.get_id) info args
+  evar_instance_array (NamedDecl.get_id %> isVarId) info args
 
 let instantiate_evar_array info c args =
   let inst = make_evar_instance_array info args in
@@ -684,7 +684,7 @@ let restrict evk filter ?candidates evd =
       evar_extra = Store.empty } in
   let evar_names = EvNames.reassign_name_defined evk evk' evd.evar_names in
   let ctxt = Filter.filter_list filter (evar_context evar_info) in
-  let id_inst = Array.map_of_list (mkVar % NamedDecl.get_id) ctxt in
+  let id_inst = Array.map_of_list (NamedDecl.get_id %> mkVar) ctxt in
   let body = mkEvar(evk',id_inst) in
   let (defn_evars, undf_evars) = define_aux evd.defn_evars evd.undf_evars evk body in
   { evd with undf_evars = EvMap.add evk' evar_info' undf_evars;
@@ -1403,7 +1403,7 @@ let print_env_short env =
     | RelDecl.LocalAssum (n,_) -> pr_name n
     | RelDecl.LocalDef (n,b,_) -> str "(" ++ pr_name n ++ str " := " ++ print_constr b ++ str ")"
   in
-  let pr_named_decl = pr_rel_decl % NamedDecl.to_rel_decl in
+  let pr_named_decl = NamedDecl.to_rel_decl %> pr_rel_decl in
   let nc = List.rev (named_context env) in
   let rc = List.rev (rel_context env) in
     str "[" ++ pr_sequence pr_named_decl nc ++ str "]" ++ spc () ++
-- 
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