/-
Copyright (c) 2018 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Author: Sebastian Ullrich

Term-level parsers
-/
prelude
import init.lean.parser.level init.lean.parser.notation
import init.lean.expr

namespace lean
namespace parser
open combinators parser.has_view monad_parsec

local postfix `?`:10000 := optional
local postfix *:10000 := combinators.many
local postfix +:10000 := combinators.many1

set_option class.instance_max_depth 200

@[derive parser.has_tokens parser.has_view]
def ident_univ_spec.parser : basic_parser :=
node! ident_univ_spec [".{", levels: level.parser+, "}"]

@[derive parser.has_tokens parser.has_view]
def ident_univs.parser : term_parser :=
node! ident_univs [id: ident.parser, univs: (monad_lift ident_univ_spec.parser)?]

namespace term
/-- Access leading term -/
def get_leading : trailing_term_parser := read
instance : has_tokens get_leading := default _
instance : has_view syntax get_leading := default _

@[derive parser.has_tokens parser.has_view]
def paren.parser : term_parser :=
node! «paren» ["(":max_prec,
  content: node! paren_content [
    term: term.parser,
    special: node_choice! paren_special {
      /- Do not allow trailing comma. Looks a bit weird and would clash with
      adding support for tuple sections (https://downloads.haskell.org/~ghc/8.2.1/docs/html/users_guide/glasgow_exts.html#tuple-sections). -/
      tuple: node! tuple [", ", tail: sep_by (term.parser 0) (symbol ", ") ff],
      typed: node! typed [" : ", type: term.parser],
    }?,
  ]?,
  ")"
]

@[derive parser.has_tokens parser.has_view]
def hole.parser : term_parser :=
node! hole [hole: symbol "_" max_prec]

@[derive parser.has_tokens parser.has_view]
def sort.parser : term_parser :=
node_choice! sort {"Sort":max_prec, "Type":max_prec}

@[derive has_tokens has_view]
def type_spec.parser : term_parser :=
node! type_spec [" : ", type: term.parser 0]

@[derive has_tokens has_view]
def opt_type.parser : term_parser :=
type_spec.parser?

instance opt_type.view_default : has_view_default opt_type.parser _ none := ⟨⟩

section binder
@[derive has_tokens has_view]
def binder_ident.parser : term_parser :=
node_choice! binder_ident {id: ident.parser, hole: hole.parser}

@[derive has_tokens has_view]
def binder_default.parser : term_parser :=
node_choice! binder_default {
  val: node! binder_default_val [":=", term: term.parser 0],
  tac: node! binder_default_tac [".", term: term.parser 0],
}

@[derive has_tokens has_view]
def binder_content.parser : term_parser :=
node! binder_content [
  ids: binder_ident.parser+,
  type: opt_type.parser,
  default: binder_default.parser?
]

@[derive has_tokens has_view]
def simple_binder.parser : term_parser :=
node_choice! simple_binder {
  explicit: node! simple_explicit_binder ["(", id: ident.parser, " : ", type: term.parser 0, right: symbol ")"],
  implicit: node! simple_implicit_binder ["{", id: ident.parser, " : ", type: term.parser 0, right: symbol "}"],
  strict_implicit: node! simple_strict_implicit_binder ["⦃", id: ident.parser, " : ", type: term.parser 0, right: symbol "⦄"],
  inst_implicit: node! simple_inst_implicit_binder ["[", id: ident.parser, " : ", type: term.parser 0, right: symbol "]"],
}

def simple_binder.view.to_binder_info : simple_binder.view → (binder_info × syntax_ident × syntax)
| (simple_binder.view.explicit {id := id, type := type})        := (binder_info.default, id, type)
| (simple_binder.view.implicit {id := id, type := type})        := (binder_info.implicit, id, type)
| (simple_binder.view.strict_implicit {id := id, type := type}) := (binder_info.strict_implicit, id, type)
| (simple_binder.view.inst_implicit {id := id, type := type})   := (binder_info.inst_implicit, id, type)

@[derive parser.has_tokens parser.has_view]
def anonymous_constructor.parser : term_parser :=
node! anonymous_constructor ["⟨":max_prec, args: sep_by (term.parser 0) (symbol ","), "⟩"]

/- All binders must be surrounded with some kind of bracket. (e.g., '()', '{}', '[]').
   We use this feature when parsing examples/definitions/theorems. The goal is to avoid counter-intuitive
   declarations such as:

     example p : false := trivial
     def main proof : false := trivial

   which would be parsed as

     example (p : false) : _ := trivial

     def main (proof : false) : _ := trivial

   where `_` in both cases is elaborated into `true`. This issue was raised by @gebner in the slack channel.


   Remark: we still want implicit delimiters for lambda/pi expressions. That is, we want to
   write

       fun x : t, s
   or
       fun x, s

   instead of

       fun (x : t), s -/
@[derive has_tokens has_view]
def bracketed_binder.parser : term_parser :=
node_choice! bracketed_binder {
  explicit: node! explicit_binder ["(", content: node_choice! explicit_binder_content {
    «notation»: command.notation_like.parser,
    other: binder_content.parser
  }, right: symbol ")"],
  implicit: node! implicit_binder ["{", content: binder_content.parser, "}"],
  strict_implicit: node! strict_implicit_binder ["⦃", content: binder_content.parser, "⦄"],
  inst_implicit: node! inst_implicit_binder ["[", content: node_longest_choice! inst_implicit_binder_content {
    named: node! inst_implicit_named_binder [id: ident.parser, " : ", type: term.parser 0],
    anonymous: node! inst_implicit_anonymous_binder [type: term.parser 0]
  }, "]"],
  anonymous_constructor: anonymous_constructor.parser,
}

@[derive has_tokens has_view]
def binder.parser : term_parser :=
node_choice! binder {
  bracketed: bracketed_binder.parser,
  unbracketed: binder_content.parser,
}

@[derive has_tokens has_view]
def binders_ext.parser : term_parser :=
node! binders_ext [
  leading_ids: binder_ident.parser*,
  remainder: node_choice! binders_remainder {
    type: node! binders_types [":", type: term.parser 0],
    -- we allow mixing like in `a (b : β) c`, but not `a : α (b : β) c : γ`
    mixed: node_choice! mixed_binder {
      bracketed: bracketed_binder.parser,
      id: binder_ident.parser,
    }+,
  }?
]

/-- We normalize binders to simpler singleton ones during expansion. -/
@[derive has_tokens has_view]
def binders.parser : term_parser :=
node_choice! binders {
  extended: binders_ext.parser,
  -- a strict subset of `extended`, so only useful after parsing
  simple: simple_binder.parser,
}

/-- We normalize binders to simpler ones during expansion. These always-bracketed
    binders are used in declarations and cannot be reduced to nested singleton binders. -/
@[derive has_tokens has_view]
def bracketed_binders.parser : term_parser :=
node_choice! bracketed_binders {
  extended: bracketed_binder.parser*,
  -- a strict subset of `extended`, so only useful after parsing
  simple: simple_binder.parser*,
}
end binder

@[derive parser.has_tokens parser.has_view]
def lambda.parser : term_parser :=
node! lambda [
  op: unicode_symbol "λ" "fun" max_prec,
  binders: binders.parser,
  ",",
  body: term.parser 0
]

@[derive parser.has_tokens parser.has_view]
def assume.parser : term_parser :=
node! «assume» [
  "assume ":max_prec,
  binders: node_choice! assume_binders {
    anonymous: node! assume_anonymous [": ", type: term.parser],
    binders: binders.parser
  },
  ", ",
  body: term.parser 0
]

@[derive parser.has_tokens parser.has_view]
def pi.parser : term_parser :=
node! pi [
  op: any_of [unicode_symbol "Π" "Pi" max_prec, unicode_symbol "∀" "forall" max_prec],
  binders: binders.parser,
  ",",
  range: term.parser 0
]

@[derive parser.has_tokens parser.has_view]
def explicit.parser : term_parser :=
node! explicit [
  mod: node_choice! explicit_modifier {
    explicit: symbol "@" max_prec,
    partial_explicit: symbol "@@" max_prec
  },
  id: ident_univs.parser
]

@[derive parser.has_tokens parser.has_view]
def from.parser : term_parser :=
node! «from» ["from ", proof: term.parser]

@[derive parser.has_tokens parser.has_view]
def let.parser : term_parser :=
node! «let» [
  "let ",
  lhs: node_choice! let_lhs {
    id: node! let_lhs_id [
      id: ident.parser,
      -- NOTE: after expansion, binders are empty
      binders: bracketed_binder.parser*,
      type: opt_type.parser,
    ],
    pattern: term.parser
  },
  " := ",
  value: term.parser,
  " in ",
  body: term.parser,
]

@[derive parser.has_tokens parser.has_view]
def opt_ident.parser : term_parser :=
(try node! opt_ident [id: ident.parser, " : "])?

@[derive parser.has_tokens parser.has_view]
def have.parser : term_parser :=
node! «have» [
  "have ",
  id: opt_ident.parser,
  prop: term.parser,
  proof: node_choice! have_proof {
    term: node! have_term [" := ", term: term.parser],
    «from»: node! have_from [", ", «from»: from.parser],
  },
  ", ",
  body: term.parser,
]

@[derive parser.has_tokens parser.has_view]
def show.parser : term_parser :=
node! «show» [
  "show ",
  prop: term.parser,
  ", ",
  «from»: from.parser,
]

@[derive parser.has_tokens parser.has_view]
def match.parser : term_parser :=
node! «match» [
  "match ",
  scrutinees: sep_by1 term.parser (symbol ", ") ff,
  type: opt_type.parser,
  " with ",
  opt_bar: (symbol " | ")?,
  equations: sep_by1
    node! «match_equation» [
      lhs: sep_by1 term.parser (symbol ", ") ff, ":=", rhs: term.parser]
    (symbol " | ") ff,
]

@[derive parser.has_tokens parser.has_view]
def if.parser : term_parser :=
node! «if» [
  "if ",
  id: opt_ident.parser,
  prop: term.parser,
  " then ",
  then_branch: term.parser,
  " else ",
  else_branch: term.parser,
]

@[derive parser.has_tokens parser.has_view]
def struct_inst.parser : term_parser :=
node! struct_inst [
  "{":max_prec,
  type: (try node! struct_inst_type [id: ident.parser, " . "])?,
  «with»: (try node! struct_inst_with [source: term.parser, " with "])?,
  items: sep_by node_choice! struct_inst_item {
    field: node! struct_inst_field [id: ident.parser, " := ", val: term.parser],
    source: node! struct_inst_source ["..", source: term.parser?],
  } (symbol ", "),
  "}",
]

@[derive parser.has_tokens parser.has_view]
def subtype.parser : term_parser :=
node! subtype [
  "{":max_prec,
  id: ident.parser,
  type: opt_type.parser,
  "//",
  prop: term.parser,
  "}"
]

@[derive parser.has_tokens parser.has_view]
def inaccessible.parser : term_parser :=
node! inaccessible [".(":max_prec, term: term.parser, ")"]

@[derive parser.has_tokens parser.has_view]
def anonymous_inaccessible.parser : term_parser :=
node! anonymous_inaccessible ["._":max_prec]

@[derive parser.has_tokens parser.has_view]
def sorry.parser : term_parser :=
node! «sorry» ["sorry":max_prec]

@[derive parser.has_tokens parser.has_view]
def borrowed.parser : term_parser :=
node! borrowed ["@&":max_prec, term: term.parser]

-- TODO(Sebastian): replace with attribute
@[derive has_tokens]
def builtin_leading_parsers : token_map term_parser := token_map.of_list [
  (`ident, ident_univs.parser),
  (number.name, number.parser),
  (string_lit.name, string_lit.parser),
  ("(", paren.parser),
  ("_", hole.parser),
  ("Sort", sort.parser),
  ("Type", sort.parser),
  ("λ", lambda.parser),
  ("fun", lambda.parser),
  ("Π", pi.parser),
  ("Pi", pi.parser),
  ("∀", pi.parser),
  ("forall", pi.parser),
  ("⟨", anonymous_constructor.parser),
  ("@", explicit.parser),
  ("@@", explicit.parser),
  ("let", let.parser),
  ("have", have.parser),
  ("show", show.parser),
  ("assume", assume.parser),
  ("match", match.parser),
  ("if", if.parser),
  ("{", struct_inst.parser),
  ("{", subtype.parser),
  (".(", inaccessible.parser),
  ("._", anonymous_inaccessible.parser),
  ("sorry", sorry.parser),
  ("@&", borrowed.parser)
]

@[derive parser.has_tokens parser.has_view]
def sort_app.parser : trailing_term_parser :=
do { l ← get_leading, guard $ l.is_of_kind sort } *>
node! sort_app [fn: get_leading, arg: monad_lift (level.parser max_prec).run]

@[derive parser.has_tokens parser.has_view]
def app.parser : trailing_term_parser :=
node! app [fn: get_leading, arg: term.parser max_prec]

def mk_app (fn : syntax) (args : list syntax) : syntax :=
args.foldl (λ fn arg, syntax.mk_node app [fn, arg]) fn

@[derive parser.has_tokens parser.has_view]
def arrow.parser : trailing_term_parser :=
node! arrow [dom: get_leading, op: unicode_symbol "→" "->" 25, range: term.parser 24]

@[derive parser.has_view]
def projection.parser : trailing_term_parser :=
try $ node! projection [
  term: get_leading,
  -- do not consume trailing whitespace
  «.»: raw_str ".",
  proj: node_choice! projection_spec {
    id: parser.ident.parser,
    num: number.parser,
  },
]

-- register '.' manually because of `raw_str`
instance projection.tokens : has_tokens projection.parser :=
/- Use max_prec + 1 so that it bind more tightly than application:
   `a (b).c` should be parsed as `a ((b).c)`. -/
⟨[{«prefix» := ".", lbp := max_prec.succ}]⟩

@[derive has_tokens]
def builtin_trailing_parsers : token_map trailing_term_parser := token_map.of_list [
  ("→", arrow.parser),
  ("->", arrow.parser),
  (".", projection.parser)
]

end term

private def trailing (cfg : command_parser_config) : trailing_term_parser :=
-- try local parsers first, starting with the newest one
(do ps ← indexed cfg.local_trailing_term_parsers, ps.foldr (<|>) (error ""))
<|>
-- next try all non-local parsers
(do ps ← indexed cfg.trailing_term_parsers, longest_match ps)
<|>
-- The application parsers should only be tried as a fall-back;
-- e.g. `a + b` should not be parsed as `a (+ b)`.
-- TODO(Sebastian): We should be able to remove this workaround using
-- the proposed more robust precedence handling
any_of [term.sort_app.parser, term.app.parser]

private def leading (cfg : command_parser_config) : term_parser :=
(do ps ← indexed cfg.local_leading_term_parsers, ps.foldr (<|>) (error ""))
<|>
(do ps ← indexed cfg.leading_term_parsers, longest_match ps)

def term_parser.run (p : term_parser) : command_parser :=
do cfg ← read,
   adapt_reader coe $ pratt_parser (leading cfg) (trailing cfg) p

end parser
end lean