syndicate-nim/src/syndicate/patterns.nim

# SPDX-FileCopyrightText: ☭ 2021 Emery Hemingway
# SPDX-License-Identifier: Unlicense

import std/[macros, tables]

import preserves
import ./protocols/dataspacePatterns
from ./actors import Ref

export dataspacePatterns.`$`

type
  CRec = dataspacePatterns.CRec[Ref]
  DCompoundRec = dataspacePatterns.DCompoundRec[Ref]
  DBind* = dataspacePatterns.DBind[Ref]
  DLit* = dataspacePatterns.DLit[Ref]
  DCompound* = dataspacePatterns.DCompound[Ref]
  Pattern* = dataspacePatterns.Pattern[Ref]

proc `?`*(d: DBind): Pattern =
  Pattern(orKind: PatternKind.DBind, dbind: d)

proc `?`*(d: DLit): Pattern =
  Pattern(orKind: PatternKind.DLit, dlit: d)

proc `?`*(d: DCompound): Pattern =
  Pattern(orKind: PatternKind.DCompound, dcompound: d)

proc `?`*(s: string): Pattern =
  ?DLit(value: toPreserve(s, Ref))

proc arity(T: typedesc): int =
  var t: T # a hack to iterate the fields of a non-existent instance
  for _ in fields(t): inc result

proc `?_`*(): Pattern = Pattern(orKind: PatternKind.DDiscard)

proc `?*`*(): Pattern = ?DBind(pattern: `?_`())

proc `?`*(T: typedesc; bindings: openArray[(int, Pattern)]): Pattern =
  ## Pattern constructor operator.
  when T.hasCustomPragma(preservesRecord):
    var label = tosymbol(T.getCustomPragmaVal(preservesRecord), Ref)
    result = ?DCompound(
      orKind: DCompoundKind.rec,
      rec: DCompoundRec(
        ctor: CRec(label: label, arity: T.arity),
        members: toTable bindings))
  else:
    {.error: "no custom pragma on " & $T.}

proc observe*(pat: Pattern): Pattern =
  # TODO: why doesn't Observe from ./protocols/dataspace.nim work?
  ?DCompound(
    orKind: DCompoundKind.rec,
    rec: DCompoundRec(
      ctor: CRec(label: toSymbol("Observe", Ref), arity: 2),
      members: toTable {0 : pat, 1: `?_`()}))