From b232963cba61e3f6bcf2d69c431baaf7c7cd8a20 Mon Sep 17 00:00:00 2001
From: Magnus Klaar <klaar@ninenines.fr>
Date: Tue, 1 May 2012 21:34:35 +0200
Subject: [PATCH] Add glc_ops module for built in operators

---
 rebar.config    |   4 ++
 src/glc_ops.erl | 111 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 115 insertions(+)
 create mode 100644 src/glc_ops.erl

diff --git a/rebar.config b/rebar.config
index 55fe764..ef5b0d8 100644
--- a/rebar.config
+++ b/rebar.config
@@ -6,3 +6,7 @@
 	warnings_as_errors,
 	warn_export_all
 ]}.
+{deps, [
+    {proper, ".*",
+        {git, "git://github.com/manopapad/proper.git", "master"}}
+]}.
diff --git a/src/glc_ops.erl b/src/glc_ops.erl
new file mode 100644
index 0000000..4be831e
--- /dev/null
+++ b/src/glc_ops.erl
@@ -0,0 +1,111 @@
+%% @doc Built in operators.
+-module(glc_ops).
+
+-export([
+    lt/2,
+    eq/2,
+    gt/2
+]).
+
+-export([
+    all/1,
+    any/1,
+    null/1,
+    with/2
+]).
+
+-export([
+    union/1
+]).
+
+-type op() ::
+    {atom(), '<', term()} |
+    {atom(), '=', term()} |
+    {atom(), '>', term()} |
+    {any, [op(), ...]} |
+    {all, [op(), ...]} |
+    {null, true|false}.
+
+-export_type([op/0]).
+
+%% @doc Test that a field value is less than a term.
+-spec lt(atom(), term()) -> op().
+lt(Key, Term) when is_atom(Key) ->
+    {Key, '<', Term};
+lt(Key, Term) ->
+    erlang:error(badarg, [Key, Term]).
+
+%% @doc Test that a field value is equal to a term.
+-spec eq(atom(), term()) -> op().
+eq(Key, Term) when is_atom(Key) ->
+    {Key, '=', Term};
+eq(Key, Term) ->
+    erlang:error(badarg, [Key, Term]).
+
+%% @doc Test that a field value is greater than a term.
+-spec gt(atom(), term()) -> op().
+gt(Key, Term) when is_atom(Key) ->
+    {Key, '>', Term};
+gt(Key, Term) ->
+    erlang:error(badarg, [Key, Term]).
+
+
+%% @doc Filter the input using multiple filters.
+%%
+%% For an input to be considered valid output the all filters specified
+%% in the list must hold for the input event. The list is expected to
+%% be a non-empty list. If the list of filters is an empty list a `badarg'
+%% error will be thrown.
+-spec all([op()]) -> op().
+all([_|_]=Conds) ->
+    {all, Conds};
+all(Other) ->
+    erlang:error(badarg, [Other]).
+
+%% @doc Filter the input using one of multiple filters.
+%%
+%% For an input to be considered valid output on of the filters specified
+%% in the list must hold for the input event. The list is expected to be
+%% a non-empty list. If the list of filters is an empty list a `badarg'
+%% error will be thrown.
+-spec any([op()]) -> op().
+any([_|_]=Conds) ->
+    {any, Conds};
+any(Other) ->
+    erlang:error(badarg, [Other]).
+
+
+%% @doc Always return `true' or `false'.
+-spec null(boolean()) -> op().
+null(Result) when is_boolean(Result) ->
+    {null, Result};
+null(Result) ->
+    erlang:error(badarg, [Result]).
+
+%% @doc Apply a function to each output of a query.
+%%
+%% Updating the output action of a query finalizes it. Attempting
+%% to use a finalized query to construct a new query will result
+%% in a `badarg' error.
+-spec with(op(), fun((gre:event()) -> term())) -> op().
+with(Query, Fun) when is_function(Fun, 1) ->
+    {with, Query, Fun};
+with(Query, Fun) ->
+    erlang:error(badarg, [Query, Fun]).
+
+%% @doc Return a union of multiple queries.
+%%
+%% The union of multiple queries is the equivalent of executing multiple
+%% queries separately on the same input event. The advantage is that filter
+%% conditions that are common to all or some of the queries only need to
+%% be tested once.
+%%
+%% All queries are expected to be valid and have an output action other
+%% than the default which is `output'. If these expectations don't hold
+%% a `badarg' error will be thrown.
+-spec union([op()]) -> op().
+union(Queries) ->
+    case [Query || Query <- Queries, glc_lib:onoutput(Query) =:= output] of
+        [] -> {union, Queries};
+        [_|_] -> erlang:error(badarg, [Queries])
+    end.