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).
---
 library/impargs.ml | 2 +-
 library/lib.ml     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

(limited to 'library')

diff --git a/library/impargs.ml b/library/impargs.ml
index 2997f94ed2..07b6b2bae3 100644
--- a/library/impargs.ml
+++ b/library/impargs.ml
@@ -520,7 +520,7 @@ let impls_of_context ctx =
   | Implicit -> Some (NamedDecl.get_id decl, Manual, (true, true))
   | _ -> None
   in
-  List.rev_map map (List.filter (is_local_assum % fst) ctx)
+  List.rev_map map (List.filter (fst %> is_local_assum) ctx)
 
 let adjust_side_condition p = function
   | LessArgsThan n -> LessArgsThan (n+p)
diff --git a/library/lib.ml b/library/lib.ml
index 412772e8af..a5a9a01942 100644
--- a/library/lib.ml
+++ b/library/lib.ml
@@ -445,7 +445,7 @@ let extract_hyps (secs,ohyps) =
   in aux (secs,ohyps)
 
 let instance_from_variable_context =
-  Array.of_list % List.map NamedDecl.get_id % List.filter is_local_assum % List.map fst
+  List.map fst %> List.filter is_local_assum %> List.map NamedDecl.get_id %> Array.of_list
 
 let named_of_variable_context =
   List.map fst
-- 
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