Make hashfn arguments work when beginning multisyms v1 PROPOSED

Benaiah Mischenko: 1
 Make hashfn arguments work when beginning multisyms

 2 files changed, 17 insertions(+), 3 deletions(-)

Phil Hagelberg <phil@hagelb.org> writes:

Export patchset (mbox)

[PATCH] Make hashfn arguments work when beginning multisyms Export this patch

Converts $ arguments to $1 when they begin a multisym (matches the
behavior of a lone $).

Sets used-local metadata correctly for symbols which begin
multisyms. This was previously incorrect for all symbols which started
multisyms, but the hashfn argument bug fixed in this commit is the
only known effect.

Added test cases for multisyms and immediately-returned arguments to
ensure neither regress.

Enables a getter function shorthand: #$symbol.property
---
 fennel.lua | 15 ++++++++++++---
 test.lua   |  5 +++++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/fennel.lua b/fennel.lua
index f68a38e..3f1a5d0 100644
--- a/fennel.lua
+++ b/fennel.lua
@@ -638,11 +638,20 @@ end
 -- if they have already been declared via declareLocal
 local function symbolToExpression(symbol, scope, isReference)
     local name = symbol[1]
-    if scope.hashfn and name == '$' then name = '$1' end
-    local parts = isMultiSym(name) or {name}
+    local multiSymParts = isMultiSym(name)
+    if scope.hashfn then
+       if name == '$' then name = '$1' end
+       if multiSymParts then
+          if multiSymParts[1] == "$" then
+             multiSymParts[1] = "$1"
+             name = table.concat(multiSymParts, ".")
+          end
+       end
+    end
+    local parts = multiSymParts or {name}
     local etype = (#parts > 1) and "expression" or "sym"
     local isLocal = scope.manglings[parts[1]]
-    if isLocal and scope.symmeta[name] then scope.symmeta[name].used = true end
+    if isLocal and scope.symmeta[parts[1]] then scope.symmeta[parts[1]].used = true end
     -- if it's a reference and not a symbol which introduces a new binding
     -- then we need to check for allowed globals
     assertCompile(not isReference or isLocal or globalAllowed(parts[1]),
diff --git a/test.lua b/test.lua
index 2c627c3..78d96b1 100644
--- a/test.lua
+++ b/test.lua
@@ -295,6 +295,8 @@ local cases = {
         ["(#(+ $3 $4) 1 1 3 4)"]=7,
         -- One argument
         ["(#(+ $1 45) 1)"]=46,
+        -- Immediately returned argument
+        ["(+ (#$ 1) (#$2 2 3))"]=4,

Phil Hagelberg

9 months ago

I like that we have #$ as a shorthand for the identity function; that
could come in handy for higher-order functions.

Next

         -- With let
         ["(let [f #(+ $1 45)] (f 1))"]=46,
         -- Complex body
@@ -303,6 +305,9 @@ local cases = {
         ["(#(+ $ 2) 3)"]=5,
         -- Mixed $ types
         ["(let [f #(+ $ $1 $2)] (f 1 2))"]=4,
+        -- Multisyms containing $ arguments
+        ["(#$.foo {:foo :bar})"]="bar",
+        ["(#$2.foo.bar.baz nil {:foo {:bar {:baz :quux}}})"]="quux",

Phil Hagelberg

9 months ago

This is very reminiscent of how Clojure treats its keywords as
functions. It's slightly more verbose, but it has the advantage of
supporting nested lookup for free. It also feels conceptually consistent
with the #$ notation above. Clojure's hashfn notation is a lot more
limited in that it requires parens after the hash, which trips a lot of
people up, and in retrospect feels like a very arbitrary rule. TBH this
makes hashfn actually seem a lot more appealing to me.

I'm in favor of this but would like to hear what others think.

If we decide to proceed we'd need to describe it in reference.md. I think
that's the only place hashfn is currently documented. A mention in the
changelog would also be warranted.

Benaiah Mischenko

9 months ago

Roger - I'll expand the documentation for hashfns, make a changelog
entry, and add those changes to the patch.

- benaiah

-Phil

     },
     match = {
         -- basic literal
-- 
2.23.0.rc1

Phil Hagelberg

9 months ago

Benaiah Mischenko <benaiah@mischenko.com> writes:

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