Nim/lib/pure/sugar.nim

#
#
#            Nim's Runtime Library
#        (c) Copyright 2015 Dominik Picheta
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

## This module implements nice syntactic sugar based on Nim's
## macro system.

import macros

proc createProcType(p, b: NimNode): NimNode {.compileTime.} =
  #echo treeRepr(p)
  #echo treeRepr(b)
  result = newNimNode(nnkProcTy)
  var formalParams = newNimNode(nnkFormalParams)

  formalParams.add b

  case p.kind
  of nnkPar, nnkTupleConstr:
    for i in 0 ..< p.len:
      let ident = p[i]
      var identDefs = newNimNode(nnkIdentDefs)
      case ident.kind
      of nnkExprColonExpr:
        identDefs.add ident[0]
        identDefs.add ident[1]
      else:
        identDefs.add newIdentNode("i" & $i)
        identDefs.add(ident)
      identDefs.add newEmptyNode()
      formalParams.add identDefs
  else:
    var identDefs = newNimNode(nnkIdentDefs)
    identDefs.add newIdentNode("i0")
    identDefs.add(p)
    identDefs.add newEmptyNode()
    formalParams.add identDefs

  result.add formalParams
  result.add newEmptyNode()
  #echo(treeRepr(result))
  #echo(result.toStrLit())

macro `=>`*(p, b: untyped): untyped =
  ## Syntax sugar for anonymous procedures.
  ##
  ## .. code-block:: nim
  ##
  ##   proc passTwoAndTwo(f: (int, int) -> int): int =
  ##     f(2, 2)
  ##
  ##   passTwoAndTwo((x, y) => x + y) # 4

  #echo treeRepr(p)
  #echo(treeRepr(b))
  var params: seq[NimNode] = @[newIdentNode("auto")]

  case p.kind
  of nnkPar, nnkTupleConstr:
    for c in children(p):
      var identDefs = newNimNode(nnkIdentDefs)
      case c.kind
      of nnkExprColonExpr:
        identDefs.add(c[0])
        identDefs.add(c[1])
        identDefs.add(newEmptyNode())
      of nnkIdent:
        identDefs.add(c)
        identDefs.add(newIdentNode("auto"))
        identDefs.add(newEmptyNode())
      of nnkInfix:
        if c[0].kind == nnkIdent and c[0].ident == !"->":
          var procTy = createProcType(c[1], c[2])
          params[0] = procTy[0][0]
          for i in 1 ..< procTy[0].len:
            params.add(procTy[0][i])
        else:
          error("Expected proc type (->) got (" & $c[0].ident & ").")
        break
      else:
        echo treeRepr c
        error("Incorrect procedure parameter list.")
      params.add(identDefs)
  of nnkIdent:
    var identDefs = newNimNode(nnkIdentDefs)
    identDefs.add(p)
    identDefs.add(newIdentNode("auto"))
    identDefs.add(newEmptyNode())
    params.add(identDefs)
  of nnkInfix:
    if p[0].kind == nnkIdent and p[0].ident == !"->":
      var procTy = createProcType(p[1], p[2])
      params[0] = procTy[0][0]
      for i in 1 ..< procTy[0].len:
        params.add(procTy[0][i])
    else:
      error("Expected proc type (->) got (" & $p[0].ident & ").")
  else:
    error("Incorrect procedure parameter list.")
  result = newProc(params = params, body = b, procType = nnkLambda)
  #echo(result.treeRepr)
  #echo(result.toStrLit())
  #return result # TODO: Bug?

macro `->`*(p, b: untyped): untyped =
  ## Syntax sugar for procedure types.
  ##
  ## .. code-block:: nim
  ##
  ##   proc pass2(f: (float, float) -> float): float =
  ##     f(2, 2)
  ##
  ##   # is the same as:
  ##
  ##   proc pass2(f: proc (x, y: float): float): float =
  ##     f(2, 2)

  result = createProcType(p, b)

type ListComprehension = object
var lc*: ListComprehension

template `|`*(lc: ListComprehension, comp: untyped): untyped = lc

macro `[]`*(lc: ListComprehension, comp, typ: untyped): untyped =
  ## List comprehension, returns a sequence. `comp` is the actual list
  ## comprehension, for example ``x | (x <- 1..10, x mod 2 == 0)``. `typ` is
  ## the type that will be stored inside the result seq.
  ##
  ## .. code-block:: nim
  ##
  ##   echo lc[x | (x <- 1..10, x mod 2 == 0), int]
  ##
  ##   const n = 20
  ##   echo lc[(x,y,z) | (x <- 1..n, y <- x..n, z <- y..n, x*x + y*y == z*z),
  ##           tuple[a,b,c: int]]

  expectLen(comp, 3)
  expectKind(comp, nnkInfix)
  assert($comp[0] == "|")

  result = newCall(
    newDotExpr(
      newIdentNode("result"),
      newIdentNode("add")),
    comp[1])

  for i in countdown(comp[2].len-1, 0):
    let x = comp[2][i]
    expectMinLen(x, 1)
    if x[0].kind == nnkIdent and $x[0].ident == "<-":
      expectLen(x, 3)
      result = newNimNode(nnkForStmt).add(x[1], x[2], result)
    else:
      result = newIfStmt((x, result))

  result = newNimNode(nnkCall).add(
    newNimNode(nnkPar).add(
      newNimNode(nnkLambda).add(
        newEmptyNode(),
        newEmptyNode(),
        newEmptyNode(),
        newNimNode(nnkFormalParams).add(
          newNimNode(nnkBracketExpr).add(
            newIdentNode("seq"),
            typ)),
        newEmptyNode(),
        newEmptyNode(),
        newStmtList(
          newAssignment(
            newIdentNode("result"),
            newNimNode(nnkPrefix).add(
              newIdentNode("@"),
              newNimNode(nnkBracket))),
          result))))


macro dump*(x: typed): untyped =
  ## Dumps the content of an expression, useful for debugging.
  ## It accepts any expression and prints a textual representation
  ## of the tree representing the expression - as it would appear in
  ## source code - together with the value of the expression.
  ##
  ## As an example,
  ##
  ## .. code-block:: nim
  ##   let
  ##     x = 10
  ##     y = 20
  ##   dump(x + y)
  ##
  ## will print ``x + y = 30``.
  let s = x.toStrLit
  let r = quote do:
    debugEcho `s`, " = ", `x`
  return r

# TODO: consider exporting this in macros.nim
proc freshIdentNodes(ast: NimNode): NimNode =
  # Replace NimIdent and NimSym by a fresh ident node
  # see also https://github.com/nim-lang/Nim/pull/8531#issuecomment-410436458
  proc inspect(node: NimNode): NimNode =
    case node.kind:
    of nnkIdent, nnkSym:
      result = ident($node)
    of nnkEmpty, nnkLiterals:
      result = node
    else:
      result = node.kind.newTree()
      for child in node:
        result.add inspect(child)
  result = inspect(ast)

macro distinctBase*(T: typedesc): untyped =
  ## reverses ``type T = distinct A``; works recursively.
  runnableExamples:
    type T = distinct int
    doAssert distinctBase(T) is int
    doAssert: not compiles(distinctBase(int))
    type T2 = distinct T
    doAssert distinctBase(T2) is int

  let typeNode = getTypeImpl(T)
  expectKind(typeNode, nnkBracketExpr)
  if typeNode[0].typeKind != ntyTypeDesc:
    error "expected typeDesc, got " & $typeNode[0]
  var typeSym = typeNode[1]
  typeSym = getTypeImpl(typeSym)
  if typeSym.typeKind != ntyDistinct:
    error "type is not distinct"
  typeSym = typeSym[0]
  while typeSym.typeKind == ntyDistinct:
    typeSym = getTypeImpl(typeSym)[0]
  typeSym.freshIdentNodes