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authorRichard Carlsson <[email protected]>2014-12-23 14:23:35 +0100
committerRichard Carlsson <[email protected]>2015-05-22 12:43:53 +0200
commite533ea29e80a641f247022f321a3bf1a1456c56e (patch)
tree2681e4a828e5393d1cc5c539efd5285b92419fa2 /lib/syntax_tools/src/merl_transform.erl
parent9a81b28598fadc44bf506354c9227e41aac786f6 (diff)
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Include Merl in Syntax Tools
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+%% ---------------------------------------------------------------------
+%% Licensed under the Apache License, Version 2.0 (the "License"); you may
+%% not use this file except in compliance with the License. You may obtain
+%% a copy of the License at <http://www.apache.org/licenses/LICENSE-2.0>
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%
+%% @author Richard Carlsson <[email protected]>
+%% @copyright 2012-2015 Richard Carlsson
+%% @doc Parse transform for merl. Enables the use of automatic metavariables
+%% and using quasi-quotes in matches and case switches. Also optimizes calls
+%% to functions in `merl' by partially evaluating them, turning strings to
+%% templates, etc., at compile-time.
+%%
+%% Using `-include_lib("syntax_tools/include/merl.hrl").' enables this
+%% transform, unless the macro `MERL_NO_TRANSFORM' is defined first.
+
+-module(merl_transform).
+
+-export([parse_transform/2]).
+
+%% NOTE: We cannot use inline metavariables or any other parse transform
+%% features in this module, because it must be possible to compile it with
+%% the parse transform disabled!
+-include("merl.hrl").
+
+%% TODO: unroll calls to switch? it will probably get messy
+
+%% TODO: use Igor to make resulting code independent of merl at runtime?
+
+parse_transform(Forms, _Options) ->
+ erl_syntax:revert_forms(expand(erl_syntax:form_list(Forms))).
+
+expand(Tree0) ->
+ Tree = pre(Tree0),
+ post(case erl_syntax:subtrees(Tree) of
+ [] ->
+ Tree;
+ Gs ->
+ erl_syntax:update_tree(Tree,
+ [[expand(T) || T <- G] || G <- Gs])
+ end).
+
+pre(T) ->
+ merl:switch(
+ T,
+ [{?Q("merl:quote(_@line, _@text) = _@expr"),
+ fun ([{expr,_}, {line,Line}, {text,Text}]) ->
+ erl_syntax:is_literal(Text) andalso erl_syntax:is_literal(Line)
+ end,
+ fun ([{expr,Expr}, {line,Line}, {text,Text}]) ->
+ pre_expand_match(Expr, erl_syntax:concrete(Line),
+ erl_syntax:concrete(Text))
+ end},
+ {?Q(["case _@expr of",
+ " merl:quote(_@_, _@text) when _@__@_ -> _@@_; _@_@_ -> 0",
+ "end"]),
+ fun case_guard/1,
+ fun (As) -> case_body(As, T) end},
+ fun () -> T end
+ ]).
+
+case_guard([{expr,_}, {text,Text}]) ->
+ erl_syntax:is_literal(Text).
+
+case_body([{expr,Expr}, {text,_Text}], T) ->
+ pre_expand_case(Expr, erl_syntax:case_expr_clauses(T),
+ erl_syntax:get_pos(T)).
+
+post(T) ->
+ merl:switch(
+ T,
+ [{?Q("merl:_@function(_@@args)"),
+ [{fun ([{args, As}, {function, F}]) ->
+ lists:all(fun erl_syntax:is_literal/1, [F|As])
+ end,
+ fun ([{args, As}, {function, F}]) ->
+ Line = erl_syntax:get_pos(F),
+ [F1|As1] = lists:map(fun erl_syntax:concrete/1, [F|As]),
+ eval_call(Line, F1, As1, T)
+ end},
+ fun ([{args, As}, {function, F}]) ->
+ merl:switch(
+ F,
+ [{?Q("qquote"), fun ([]) -> expand_qquote(As, T, 1) end},
+ {?Q("subst"), fun ([]) -> expand_template(F, As, T) end},
+ {?Q("match"), fun ([]) -> expand_template(F, As, T) end},
+ fun () -> T end
+ ])
+ end]},
+ fun () -> T end]).
+
+expand_qquote([Line, Text, Env], T, _) ->
+ case erl_syntax:is_literal(Line) of
+ true ->
+ expand_qquote([Text, Env], T, erl_syntax:concrete(Line));
+ false ->
+ T
+ end;
+expand_qquote([Text, Env], T, Line) ->
+ case erl_syntax:is_literal(Text) of
+ true ->
+ As = [Line, erl_syntax:concrete(Text)],
+ %% expand further if possible
+ expand(merl:qquote(Line, "merl:subst(_@tree, _@env)",
+ [{tree, eval_call(Line, quote, As, T)},
+ {env, Env}]));
+ false ->
+ T
+ end;
+expand_qquote(_As, T, _StartPos) ->
+ T.
+
+expand_template(F, [Pattern | Args], T) ->
+ case erl_syntax:is_literal(Pattern) of
+ true ->
+ Line = erl_syntax:get_pos(Pattern),
+ As = [erl_syntax:concrete(Pattern)],
+ merl:qquote(Line, "merl:_@function(_@pattern, _@args)",
+ [{function, F},
+ {pattern, eval_call(Line, template, As, T)},
+ {args, Args}]);
+ false ->
+ T
+ end;
+expand_template(_F, _As, T) ->
+ T.
+
+eval_call(Line, F, As, T) ->
+ try apply(merl, F, As) of
+ T1 when F =:= quote ->
+ %% lift metavariables in a template to Erlang variables
+ Template = merl:template(T1),
+ Vars = merl:template_vars(Template),
+ case lists:any(fun is_inline_metavar/1, Vars) of
+ true when is_list(T1) ->
+ merl:qquote(Line, "merl:tree([_@template])",
+ [{template, merl:meta_template(Template)}]);
+ true ->
+ merl:qquote(Line, "merl:tree(_@template)",
+ [{template, merl:meta_template(Template)}]);
+ false ->
+ merl:term(T1)
+ end;
+ T1 ->
+ merl:term(T1)
+ catch
+ throw:_Reason -> T
+ end.
+
+pre_expand_match(Expr, Line, Text) ->
+ {Template, Out, _Vars} = rewrite_pattern(Line, Text),
+ merl:qquote(Line, "{ok, _@out} = merl:match(_@template, _@expr)",
+ [{expr, Expr},
+ {out, Out},
+ {template, erl_syntax:abstract(Template)}]).
+
+rewrite_pattern(Line, Text) ->
+ %% we must rewrite the metavariables in the pattern to use lowercase,
+ %% and then use real matching to bind the Erlang-level variables
+ T0 = merl:template(merl:quote(Line, Text)),
+ Vars = [V || V <- merl:template_vars(T0), is_inline_metavar(V)],
+ {merl:alpha(T0, [{V, var_to_tag(V)} || V <- Vars]),
+ erl_syntax:list([erl_syntax:tuple([erl_syntax:abstract(var_to_tag(V)),
+ erl_syntax:variable(var_name(V))])
+ || V <- Vars]),
+ Vars}.
+
+var_name(V) when is_integer(V) ->
+ V1 = if V > 99, (V rem 100) =:= 99 ->
+ V div 100;
+ V > 9, (V rem 10) =:= 9 ->
+ V div 10;
+ true -> V
+ end,
+ list_to_atom("Q" ++ integer_to_list(V1));
+var_name(V) -> V.
+
+var_to_tag(V) when is_integer(V) -> V;
+var_to_tag(V) ->
+ list_to_atom(string:to_lower(atom_to_list(V))).
+
+pre_expand_case(Expr, Clauses, Line) ->
+ merl:qquote(Line, "merl:switch(_@expr, _@clauses)",
+ [{clauses, erl_syntax:list([pre_expand_case_clause(C)
+ || C <- Clauses])},
+ {expr, Expr}]).
+
+pre_expand_case_clause(T) ->
+ %% note that the only allowed non ``?Q(...) -> ...'' clause is ``_ -> ...''
+ merl:switch(
+ T,
+ [{?Q("(merl:quote(_@line, _@text)) when _@__@guard -> _@@body"),
+ fun ([{body,_}, {guard,_}, {line,Line}, {text,Text}]) ->
+ erl_syntax:is_literal(Text) andalso erl_syntax:is_literal(Line)
+ end,
+ fun ([{body,Body}, {guard,Guard}, {line,Line}, {text,Text}]) ->
+ pre_expand_case_clause(Body, Guard, erl_syntax:concrete(Line),
+ erl_syntax:concrete(Text))
+ end},
+ {?Q("_ -> _@@body"),
+ fun (Env) -> merl:qquote("fun () -> _@body end", Env) end}
+ ]).
+
+pre_expand_case_clause(Body, Guard, Line, Text) ->
+ %% this is similar to a meta-match ``?Q("...") = Term''
+ %% (note that the guards may in fact be arbitrary expressions)
+ {Template, Out, Vars} = rewrite_pattern(Line, Text),
+ GuardExprs = rewrite_guard(Guard),
+ Param = [{body, Body},
+ {guard,GuardExprs},
+ {out, Out},
+ {template, erl_syntax:abstract(Template)},
+ {unused, dummy_uses(Vars)}],
+ case GuardExprs of
+ [] ->
+ merl:qquote(Line, ["{_@template, ",
+ " fun (_@out) -> _@unused, _@body end}"],
+ Param);
+ _ ->
+ merl:qquote(Line, ["{_@template, ",
+ " fun (_@out) -> _@unused, _@guard end, ",
+ " fun (_@out) -> _@unused, _@body end}"],
+ Param)
+ end.
+
+%% We have to insert dummy variable uses at the beginning of the "guard" and
+%% "body" function bodies to avoid warnings for unused variables in the
+%% generated code. (Expansions at the Erlang level can't be marked up as
+%% compiler generated to allow later compiler stages to ignore them.)
+dummy_uses(Vars) ->
+ [?Q("_ = _@var", [{var, erl_syntax:variable(var_name(V))}])
+ || V <- Vars].
+
+rewrite_guard([]) -> [];
+rewrite_guard([D]) -> [make_orelse(erl_syntax:disjunction_body(D))].
+
+make_orelse([]) -> [];
+make_orelse([C]) -> make_andalso(erl_syntax:conjunction_body(C));
+make_orelse([C | Cs]) ->
+ ?Q("_@expr orelse _@rest",
+ [{expr, make_andalso(erl_syntax:conjunction_body(C))},
+ {rest, make_orelse(Cs)}]).
+
+make_andalso([E]) -> E;
+make_andalso([E | Es]) ->
+ ?Q("_@expr andalso _@rest", [{expr, E}, {rest, make_andalso(Es)}]).
+
+is_inline_metavar(Var) when is_atom(Var) ->
+ is_erlang_var(atom_to_list(Var));
+is_inline_metavar(Var) when is_integer(Var) ->
+ Var > 9 andalso (Var rem 10) =:= 9;
+is_inline_metavar(_) -> false.
+
+is_erlang_var([C|_]) when C >= $A, C =< $Z ; C >= $À, C =< $Þ, C /= $× ->
+ true;
+is_erlang_var(_) ->
+ false.