doc: describe all simp configuration options

src/Init/MetaTypes.lean

@@ -68,45 +68,116 @@ namespace Simp
 
 def defaultMaxSteps := 100000
 
+/--
+The configuration for `simp`.
+Passed to `simp` using, for example, the `simp (config := {contextual := true})` syntax.
+
+See also `Lean.Meta.Simp.neutralConfig`.
+-/
 structure Config where
+  /--
+  The maximum number of subexpressions to visit when performing simplification.
+  The default is 100000.
+  -/
   maxSteps          : Nat  := defaultMaxSteps
+  /--
+  When simp discharges side conditions for conditional lemmas, it can recursively apply simplification.
+  The `maxDischargeDepth` (default: 2) is the maximum recursion depth when recursively applying simplification to side conditions.
+  -/
   maxDischargeDepth : Nat  := 2
+  /--
+  When `contextual` is true (default: `false`) and simplification encounters an implication `p → q`
+  it includes `p` as an additional simp lemma when simplifying `q`.
+  -/
   contextual        : Bool := false
+  /--
+  When true (default: `true`) then the simplifier caches the result of simplifying each subexpression, if possible.
+  -/
   memoize           : Bool := true
+  /--
+  When `singlePass` is `true` (default: `false`), the simplifier runs through a single round of simplification,
+  which consists of running pre-methods, recursing using congruence lemmas, and then running post-methods.
+  Otherwise, when it is `false`, it iteratively applies this simplification procedure.
+  -/
   singlePass        : Bool := false
-  /-- `let x := v; e[x]` reduces to `e[v]`. -/
+  /--
+  When `true` (default: `true`), performs zeta reduction of let expressions.
+  That is, `let x := v; e[x]` reduces to `e[v]`.
+  See also `zetaDelta`.
+  -/
   zeta              : Bool := true
+  /--
+  When `true` (default: `true`), performs beta reduction of applications of `fun` expressions.
+  That is, `(fun x => e[x]) v` reduces to `e[v]`.
+  -/
   beta              : Bool := true
+  /--
+  TODO (currently unimplemented). When `true` (default: `true`), performs eta reduction for `fun` expressions.
+  That is, `(fun x => f x)` reduces to `f`.
+  -/
   eta               : Bool := true
+  /--
+  Configures how to determine definitional equality between two structure instances.
+  See documentation for `Lean.Meta.EtaStructMode`.
+  -/
   etaStruct         : EtaStructMode := .all
+  /--
+  When `true` (default: `true`), reduces `match` expressions applied to constructors.
+  -/
   iota              : Bool := true
+  /--
+  When `true` (default: `true`), reduces projections of structure constructors.
+  -/
   proj              : Bool := true
+  /--
+  When `true` (default: `true`), rewrites a proposition `p` to `True` or `False` by inferring
+  a `Decidable p` instance and reducing it.
+  -/
   decide            : Bool := false
+  /--  When `true` (default: `false`), simplifies simple arithmetic expressions. -/
   arith             : Bool := false
+  /--
+  When `true` (default: `false`), unfolds definitions.
+  This can be enabled using the `simp!` syntax.
+  -/
   autoUnfold        : Bool := false
   /--
-    If `dsimp := true`, then switches to `dsimp` on dependent arguments where there is no congruence theorem that allows
-    `simp` to visit them. If `dsimp := false`, then argument is not visited.
+  When `true` (default: `true`) then switches to `dsimp` on dependent arguments
+  if there is no congruence theorem that would allow `simp` to visit them.
+  When `dsimp` is `false`, then the argument is not visited.
   -/
   dsimp             : Bool := true
-  /-- If `failIfUnchanged := true`, then calls to `simp`, `dsimp`, or `simp_all`
-  will fail if they do not make progress. -/
+  /--
+  If `failIfUnchanged` is `true` (default: `true`), then calls to `simp`, `dsimp`, or `simp_all`
+  will fail if they do not make progress.
+  -/
   failIfUnchanged   : Bool := true
-  /-- If `ground := true`, then ground terms are reduced. A term is ground when
-  it does not contain free or meta variables. Reduction is interrupted at a function application `f ...`
-  if `f` is marked to not be unfolded. -/
+  /--
+  If `ground` is `true` (default: `false`), then ground terms are reduced.
+  A term is ground when it does not contain free or meta variables.
+  Reduction is interrupted at a function application `f ...` if `f` is marked to not be unfolded.
+  Ground term reduction applies `@[seval]` lemmas.
+  -/
   ground            : Bool := false
-  /-- If `unfoldPartialApp := true`, then calls to `simp`, `dsimp`, or `simp_all`
-  will unfold even partial applications of `f` when we request `f` to be unfolded. -/
+  /--
+  If `unfoldPartialApp` is `true` (default: `false`), then calls to `simp`, `dsimp`, or `simp_all`
+  will unfold even partial applications of `f` when we request `f` to be unfolded.
+  -/
   unfoldPartialApp  : Bool := false
-  /-- Given a local context containing entry `x : t := e`, free variable `x` reduces to `e`. -/
+  /--
+  When `true` (default: `false`), local definitions are unfolded.
+  That is, given a local context containing entry `x : t := e`, the free variable `x` reduces to `e`.
+  -/
   zetaDelta         : Bool := false
   deriving Inhabited, BEq
 
 -- Configuration object for `simp_all`
 structure ConfigCtx extends Config where
   contextual := true
 
+/--
+A neutral configuration for `simp`, turning off all reductions and other built-in simplifications.
+-/
 def neutralConfig : Simp.Config := {
   zeta              := false
   beta              := false