Repr.lean

/-
Copyright (c) 2020 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Leonardo de Moura
-/
prelude
import Lean.Meta.Transform
import Lean.Meta.Inductive
import Lean.Elab.Deriving.Basic
import Lean.Elab.Deriving.Util

namespace Lean.Elab.Deriving.Repr
open Lean.Parser.Term
open Meta
open Std

def mkReprHeader (indVal : InductiveVal) : TermElabM Header := do
  let header ← mkHeader `Repr 1 indVal
  return { header with
    binders := header.binders.push (← `(bracketedBinderF| (prec : Nat)))
  }

def mkBodyForStruct (header : Header) (indVal : InductiveVal) : TermElabM Term := do
  let ctorVal ← getConstInfoCtor indVal.ctors.head!
  let fieldNames := getStructureFields (← getEnv) indVal.name
  let numParams  := indVal.numParams
  let target     := mkIdent header.targetNames[0]!
  forallTelescopeReducing ctorVal.type fun xs _ => do
    let mut fields ← `(Format.nil)
    if xs.size != numParams + fieldNames.size then
      throwError "'deriving Repr' failed, unexpected number of fields in structure"
    for i in [:fieldNames.size] do
      let fieldName := fieldNames[i]!
      let fieldNameLit := Syntax.mkStrLit (toString fieldName)
      let x := xs[numParams + i]!
      if i != 0 then
        fields ← `($fields ++ "," ++ Format.line)
      if (← isType x <||> isProof x) then
        fields ← `($fields ++ $fieldNameLit ++ " := " ++ "_")
      else
        let indent := Syntax.mkNumLit <| toString ((toString fieldName |>.length) + " := ".length)
        fields ← `($fields ++ $fieldNameLit ++ " := " ++ (Format.group (Format.nest $indent (repr ($target.$(mkIdent fieldName):ident)))))
    `(Format.bracket "{ " $fields:term " }")

def mkBodyForInduct (header : Header) (indVal : InductiveVal) (auxFunName : Name) : TermElabM Term := do
  let discrs ← mkDiscrs header indVal
  let alts ← mkAlts
  `(match $[$discrs],* with $alts:matchAlt*)
where
  mkAlts : TermElabM (Array (TSyntax ``matchAlt)) := do
    let mut alts := #[]
    for ctorName in indVal.ctors do
      let ctorInfo ← getConstInfoCtor ctorName
      let alt ← forallTelescopeReducing ctorInfo.type fun xs _ => do
        let mut patterns := #[]
        -- add `_` pattern for indices
        for _ in [:indVal.numIndices] do
          patterns := patterns.push (← `(_))
        let mut ctorArgs := #[]
        let mut rhs : Term := Syntax.mkStrLit (toString ctorInfo.name)
        rhs ← `(Format.text $rhs)
        -- add `_` for inductive parameters, they are inaccessible
        for _ in [:indVal.numParams] do
          ctorArgs := ctorArgs.push (← `(_))
        for i in [:ctorInfo.numFields] do
          let x := xs[indVal.numParams + i]!
          let a := mkIdent (← mkFreshUserName `a)
          ctorArgs := ctorArgs.push a
          let localDecl ← x.fvarId!.getDecl
          if localDecl.binderInfo.isExplicit then
            if (← inferType x).isAppOf indVal.name then
              rhs ← `($rhs ++ Format.line ++ $(mkIdent auxFunName):ident $a:ident max_prec)
            else
              rhs ← `($rhs ++ Format.line ++ reprArg $a)
        patterns := patterns.push (← `(@$(mkIdent ctorName):ident $ctorArgs:term*))
        `(matchAltExpr| | $[$patterns:term],* => Repr.addAppParen (Format.group (Format.nest (if prec >= max_prec then 1 else 2) ($rhs:term))) prec)
      alts := alts.push alt
    return alts

def mkBody (header : Header) (indVal : InductiveVal) (auxFunName : Name) : TermElabM Term := do
  if isStructure (← getEnv) indVal.name then
    mkBodyForStruct header indVal
  else
    mkBodyForInduct header indVal auxFunName

def mkAuxFunction (ctx : Context) (i : Nat) : TermElabM Command := do
  let auxFunName := ctx.auxFunNames[i]!
  let indVal     := ctx.typeInfos[i]!
  let header     ← mkReprHeader indVal
  let mut body   ← mkBody header indVal auxFunName
  if ctx.usePartial then
    let letDecls ← mkLocalInstanceLetDecls ctx `Repr header.argNames
    body ← mkLet letDecls body
  let binders    := header.binders
  if ctx.usePartial then
    `(private partial def $(mkIdent auxFunName):ident $binders:bracketedBinder* : Format := $body:term)
  else
    `(private def $(mkIdent auxFunName):ident $binders:bracketedBinder* : Format := $body:term)

def mkMutualBlock (ctx : Context) : TermElabM Syntax := do
  let mut auxDefs := #[]
  for i in [:ctx.typeInfos.size] do
    auxDefs := auxDefs.push (← mkAuxFunction ctx i)
  `(mutual
     $auxDefs:command*
    end)

private def mkReprInstanceCmd (declName : Name) : TermElabM (Array Syntax) := do
  let ctx ← mkContext "repr" declName
  let cmds := #[← mkMutualBlock ctx] ++ (← mkInstanceCmds ctx `Repr #[declName])
  trace[Elab.Deriving.repr] "\n{cmds}"
  return cmds

open Command

def mkReprInstanceHandler (declNames : Array Name) : CommandElabM Bool := do
  if (← declNames.allM isInductive) then
    for declName in declNames do
      let cmds ← liftTermElabM <| mkReprInstanceCmd declName
      cmds.forM elabCommand
    return true
  else
    return false

builtin_initialize
  registerDerivingHandler `Repr mkReprInstanceHandler
  registerTraceClass `Elab.Deriving.repr

end Lean.Elab.Deriving.Repr