From ba3ad6b1bca388d8bf9689ff493cc69b8420105c Mon Sep 17 00:00:00 2001
From: Joseph Ferano <joseph@ferano.io>
Date: Sat, 26 Sep 2026 01:05:00 +0700
Subject: [PATCH] In a .fln buffer ik takes the value on a one-line else or
 elif line, a wrapped fn header's return type is coloured, and C-u C-c C-c on
 a let the let above merges in stops at its value

---
 emacs/flan-fln-mode.el      | 58 ++++++++++++++++++++++++++++++++-----
 emacs/test-flan-fln-live.el | 10 ++++++-
 emacs/test-flan-fln.el      | 25 ++++++++++++++++
 3 files changed, 85 insertions(+), 8 deletions(-)

diff --git a/emacs/flan-fln-mode.el b/emacs/flan-fln-mode.el
index 50db36f2..34b3cdad 100644
--- a/emacs/flan-fln-mode.el
+++ b/emacs/flan-fln-mode.el
@@ -285,6 +285,23 @@ depth, outside strings and comments, or nil."
                                (flan-fln--joined-end l))))
     (and m (car m))))
 
+(defun flan-fln--clause-value (l)
+  "Bounds of the value on the clause line L itself: `x' of `else x' or of
+`elif c then x'; nil when the clause's value is its block."
+  (let ((end (flan-fln--joined-end l))
+        (then (flan-fln--then l)))
+    (save-excursion
+      (goto-char (flan-fln--first-char l))
+      (cond
+       ((and (looking-at "elif[ \t]") then)
+        (goto-char then)
+        (skip-chars-forward " \t")
+        (forward-char 4)
+        (skip-chars-forward " \t")
+        (and (< (point) end) (cons (point) end)))
+       ((and (looking-at "else[ \t]+") (< (match-end 0) end))
+        (cons (match-end 0) end))))))
+
 (defun flan-fln--value-start (l)
   "Where the value of the joined line L starts, after its first `=' or
 `+=' at the line's own depth, or nil when it binds or assigns nothing."
@@ -675,7 +692,21 @@ forms, where the clause line itself is not."
      (arm (plist-get arm :value))
      ((and l (flan-fln--clause-line-p l)) (flan-fln--clause-target l))
      (t (let ((s (flan-fln--statement-start-at pos)))
-          (and s (flan-fln--statement-bounds s)))))))
+          (and s (or (flan-fln--merged-let-value s)
+                     (flan-fln--statement-bounds s))))))))
+
+(defun flan-fln--merged-let-value (s)
+  "Bounds of the value of the `let' at S when the let before it takes it in.
+The reader merges consecutive lets into one binding vector, so a second
+`let b = 2' starts no form of its own; its value, or its value's block, is
+the form that runs where the line stands."
+  (let ((p (and (flan-fln--let-p s) (flan-fln--sibling s -1))))
+    (when (and p (flan-fln--let-p p))
+      (let ((v (flan-fln--value-start s))
+            (end (flan-fln--joined-end s)))
+        (if (and v (< v end))
+            (cons v (cdr (flan-fln--statement-bounds s)))
+          (flan-fln--body-bounds s))))))
 
 (defun flan-fln--clause-target (l)
   "What a clause line L stops at: an elif's condition, else its block.
@@ -686,8 +717,7 @@ A one-line `else x' stops at x."
       (cond
        ((looking-at "elif[ \t]+")
         (cons (match-end 0) (or (flan-fln--then l) end)))
-       ((and (looking-at "else[ \t]+") (< (match-end 0) end))
-        (cons (match-end 0) end))
+       ((flan-fln--clause-value l))
        (t (flan-fln--body-bounds l))))))
 
 (defun flan-fln--condition (l)
@@ -1505,8 +1535,20 @@ lambda or a `Fn(...)' type, and not after a match arm's."
         (setq found (save-excursion
                       (save-match-data
                         (goto-char (line-beginning-position))
-                        (re-search-forward "\\(?:^[ \t]*fn-?[ \t]\\|\\_<C?[fF]n(\\)"
-                                           arrow t))))))
+                        (or (re-search-forward "\\(?:^[ \t]*fn-?[ \t]\\|\\_<C?[fF]n(\\)"
+                                               arrow t)
+                            ;; A header wrapped inside its parentheses: the
+                            ;; `)' before the arrow closes a `fn f(' above.
+                            (progn
+                              (goto-char arrow)
+                              (skip-chars-backward " \t")
+                              (and (eq (char-before) ?\))
+                                   (let ((open (ignore-errors (scan-lists (point) -1 0))))
+                                     (and open
+                                          (progn
+                                            (goto-char open)
+                                            (looking-back "\\(?:^[ \t]*fn-?[ \t]+[^][ \t\n(){},;\":]+\\|\\_<C?[fF]n\\)"
+                                                          (line-beginning-position)))))))))))))
     found))
 
 (defvar flan-fln-font-lock-keywords
@@ -1777,10 +1819,12 @@ below a form is not taken: it belongs to what follows."
                          (bounds-of-thing-at-point 'flan-fln-statement))
                         'line))
       (evil-define-text-object flan-fln-inner-clause (count &optional _beg _end _type)
-        "A clause's block, its lines; a match arm's value when it is on the line."
+        "A clause's block, its lines; the value on the line of a match arm, a
+one-line else or an elif's `then'."
         (let* ((c (flan-fln--clause-at (point)))
                (arm (and c (flan-fln--arm c)))
-               (v (and arm (plist-get arm :value))))
+               (v (if arm (plist-get arm :value)
+                    (and c (flan-fln--clause-value c)))))
           (if (and v (= (flan-fln--bol (car v)) c))
               (flan-fln--evil v 'exclusive)
             (flan-fln--evil (flan-fln--whole-lines (and c (flan-fln--body-bounds c)))
diff --git a/emacs/test-flan-fln-live.el b/emacs/test-flan-fln-live.el
index 4c6d3a06..5c36ff93 100644
--- a/emacs/test-flan-fln-live.el
+++ b/emacs/test-flan-fln-live.el
@@ -74,6 +74,12 @@ fn rs() -> i64
   restart retry() \"Try again\"
     4
 
+fn t2(k: i64) -> i64
+  let a = 1
+  let b = 2
+  let c: i64 = 3
+  a + b + c + k
+
 fn dir(d: Dir) -> i64
   match d
     Dir.north -> 7
@@ -276,7 +282,9 @@ comment():
                    ("a: i64, b" "a typed lambda, from its fn")
                    ("a * 2" "a typed lambda's block")
                    ("restart retry" "a restart with a report, at its block")
-                   ("Dir.north" "an enum member's arm, at its value")))
+                   ("Dir.north" "an enum member's arm, at its value")
+                   ("let b = 2" "a let the let above takes in, at its value")
+                   ("let c: i64" "a typed one, at its value")))
         (funcall goto (car c))
         (let ((reply (flan-fln-eval-defun '(4))))
           (test-flan--check (funcall name (format "C-u C-c C-c marks %s where the reader starts it"
diff --git a/emacs/test-flan-fln.el b/emacs/test-flan-fln.el
index 544fb8a0..10721aaf 100644
--- a/emacs/test-flan-fln.el
+++ b/emacs/test-flan-fln.el
@@ -639,6 +639,18 @@ of its line with AT-END."
 (test-flan-fln--is "an else x after a block if too"
                    (cadr (test-flan-fln--oneline-at "else 2" (lambda () (flan-fln-eval-defun '(4)))))
                    '(9 8))
+(test-flan-fln--is "C-u C-c C-c on a let the let above takes in stops at its value"
+                   (test-flan-fln--in "fn t2(n: i64) -> i64\n  let a = 1\n  |let b = 2\n  a + b + n\n"
+                     (plist-get (test-flan-fln--sending (flan-fln-eval-defun '(4))) :pause))
+                   '(3 11))
+(test-flan-fln--is "and at its block when the value is one"
+                   (test-flan-fln--in "fn t2(n: i64) -> i64\n  let a = 1\n  |let b =\n    n + 1\n  a + b\n"
+                     (plist-get (test-flan-fln--sending (flan-fln-eval-defun '(4))) :pause))
+                   '(4 5))
+(test-flan-fln--is "the first let of a run stops at the let"
+                   (test-flan-fln--in "fn t2(n: i64) -> i64\n  n + 1\n  |let a = 1\n  a\n"
+                     (plist-get (test-flan-fln--sending (flan-fln-eval-defun '(4))) :pause))
+                   '(3 3))
 (test-flan-fln--is "C-c C-e on a let whose value is a block sends its scope with it"
                    (car (test-flan-fln--oneline-at "let r" #'flan-fln-eval-statement))
                    "let r = match n\n    0 -> 1\n    _ -> 2\n  add(r, 1)")
@@ -699,6 +711,13 @@ of its line with AT-END."
     (test-flan-fln--is "an enum member as a constant" (funcall face "Dir.north") 'font-lock-constant-face)
     (test-flan-fln--is "an arm's value is not a type" (funcall face "twice(1)") nil)
     (test-flan-fln--is "nor after a pattern with parentheses" (funcall face "r\n") nil)))
+(test-flan-fln--in "fn far(a: i64,\n       b: i64) -> Point\n  match a\n    Some(x) -> Other\n"
+  (font-lock-ensure)
+  (let ((face (lambda (needle)
+                (save-excursion (goto-char (point-min)) (search-forward needle)
+                                (get-text-property (match-beginning 0) 'face)))))
+    (test-flan-fln--is "a wrapped fn header's return type is a type" (funcall face "Point") 'font-lock-type-face)
+    (test-flan-fln--is "an arm's value after a call pattern is not" (funcall face "Other") nil)))
 
 ;;; Indentation
 
@@ -954,6 +973,12 @@ of its line with AT-END."
                         "5")
                        ("yak" ,(test-flan-fln--at test-flan-fln--wrapped "Some(_)")
                         "    Some(_) -> 5\n")
+                       ("yik" ,(test-flan-fln--at test-flan-fln--oneline "else 1")
+                        "1")
+                       ("yik" ,(test-flan-fln--at test-flan-fln--oneline "elif n")
+                        "0")
+                       ("yik" ,(test-flan-fln--at test-flan-fln--oneline "else 2")
+                        "2")
                        ("yid" ,(test-flan-fln--at test-flan-fln--settle "paint-at")
                         ,(substring test-flan-fln--settle
                                     (string-search "fn step" test-flan-fln--settle)))))