The other day I was talking with a friend and I said Elixir basically has no
keywords, relatively little syntax, and we can look up a lot of things like
`iex> h if`. Most of the things we'd look up are `fun` and `mod.fun` but
others, especially operators, you need to know how to write it for `h` to
accept it. For example:
```
iex> h %{}
iex> h Kernel.*
iex> h Kernel.&&
iex> h Kernel.SpecialForms.&
iex> h Kernel.SpecialForms.::
```
Today we have this:
```
iex> h 1 + 2
The "h" helper expects a Module, Module.fun or Module.fun/arity, got: 3
If instead of accessing documentation you would like more information about a
value or about the result of an expression, use the "i" helper instead
```
I'd like to propose allowing arbitrary expressions in `h` so that we teach
people to copy-paste whatever they are looking at to learn more:
```
iex> h 1 + 2
The "h" helper expects a Module, Module.fun or Module.fun/arity, got: 1 + 2
To learn about + operator, do:
iex> h Kernel.+
```
With this I believe it would be easy to learn about otherwise kind of hard to
discover things:
```elixir
iex> h %{map | k: v} # info on map update syntax
iex> h ~D[2025-01-01] # info on sigil_D
iex> h @compile # info on module attributes and/or that particular one
iex> h &is_atom/1 # info on captures
iex> h a..b
iex> h _
```
Another idea, and this is probably a bridge to far, is special casing in the
IEx evaluator `h` so that:
```
iex> h &
```
just works (as opposed to wait until the expression is completed).
I believe the implementation should be fairly straightforward:
```
diff --git a/lib/iex/lib/iex/helpers.ex b/lib/iex/lib/iex/helpers.ex
index 8964954aa..673f3abca 100644
--- a/lib/iex/lib/iex/helpers.ex
+++ b/lib/iex/lib/iex/helpers.ex
@@ -360,6 +360,22 @@ def h() do
iex> h(Enum.all?)
"""
+ defmacro h({:+, _, [_, _]} = ast) do
+ puts_error("""
+ The "h" helper expects a Module, Module.fun or Module.fun/arity, got:
#{Macro.to_string(ast)}
+
+ To learn about + operator, do:
+
+ iex> h Kernel.+
+ """)
+
+ dont_display_result()
+ end
+
+ defp puts_error(string) do
+ IO.puts(IEx.color(:eval_error, string))
+ end
+
defmacro h(term) do
quote do
IEx.Introspection.h(unquote(IEx.Introspection.decompose(term,
__CALLER__)))
```
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