fdd5aec172
This refactors and improves the `#eval` command, introducing some new
features.
* Now evaluated results can be represented using `ToExpr` and pretty
printing. This means **hoverable output**. If `ToExpr` fails, it then
tries `Repr` and then `ToString`. The `eval.pp` option controls whether
or not to try `ToExpr`.
* There is now **auto-derivation** of `Repr` instances, enabled with the
`pp.derive.repr` option (default to **true**). For example:
```lean
inductive Baz
| a | b
#eval Baz.a
-- Baz.a
```
It simply does `deriving instance Repr for Baz` when there's no way to
represent `Baz`. If core Lean gets `ToExpr` derive handlers, they could
be used here as well.
* The option `eval.type` controls whether or not to include the type in
the output. For now the default is false.
* Now things like `#eval do return 2` work. It tries using
`CommandElabM`, `TermElabM`, or `IO` when the monad is unknown.
* Now there is no longer `Lean.Eval` or `Lean.MetaEval`. These each used
to be responsible for both adapting monads and printing results. The
concerns have been split into two. (1) The `MonadEval` class is
responsible for adapting monads for evaluation (it is similar to
`MonadLift`, but instances are allowed to use default data when
initializing state) and (2) finding a way to represent results is
handled separately.
* Error messages about failed instance synthesis are now more precise.
Once it detects that a `MonadEval` class applies, then the error message
will be specific about missing `ToExpr`/`Repr`/`ToString` instances.
* Fixes a bug where `Repr`/`ToString` instances can't be found by
unfolding types "under the monad". For example, this works now:
```lean
def Foo := List Nat
def Foo.mk (l : List Nat) : Foo := l
#eval show Lean.CoreM Foo from do return Foo.mk [1,2,3]
```
* Elaboration errors now abort evaluation. This eliminates some
not-so-relevant error messages.
* Now evaluating a value of type `m Unit` never prints a blank message.
* Fixes bugs where evaluating `MetaM` and `CoreM` wouldn't collect log
messages.
The `run_cmd`, `run_elab`, and `run_meta` commands are now frontends for
`#eval`.
43 lines
782 B
Text
43 lines
782 B
Text
abbrev M := ExceptT String $ ExceptT Nat $ StateM Nat
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def inc (x : Nat) : M Unit := do
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if (← get) >= 100 then
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throwThe Nat ((← get) + x)
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modify (· + x)
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def dec (x : Nat) : M Unit := do
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if (← get) - x == 0 then
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throw "balance is zero"
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modify (· - x)
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def f (x y : Nat) : M Nat := do
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try
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inc x
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dec y
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get
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catch ex : String =>
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dbg_trace "string exception {ex}"
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pure 1000
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catch ex : Nat =>
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dbg_trace "nat exception {ex}"
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pure ex
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/--
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info: nat exception 1010
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---
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info: (Except.ok (Except.ok 1010), 1000)
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-/
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#guard_msgs in
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#eval (f 10 20).run 1000
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/--
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info: string exception balance is zero
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---
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info: (Except.ok (Except.ok 1000), 20)
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-/
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#guard_msgs in
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#eval (f 10 200).run 10
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/-- info: (Except.ok (Except.ok 20), 20) -/
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#guard_msgs in
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#eval (f 10 20).run 30
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