Add simplify-named-let-initialization refactoring rule

default-recommendations.rkt

@@ -37,6 +37,7 @@
                resyntax/default-recommendations/mutability-predicates
                resyntax/default-recommendations/numeric-shortcuts
                resyntax/default-recommendations/require-and-provide-suggestions
+               resyntax/default-recommendations/simplify-named-let-initialization
                resyntax/default-recommendations/string-shortcuts
                resyntax/default-recommendations/syntax-shortcuts
                resyntax/default-recommendations/syntax-parse-shortcuts
@@ -79,6 +80,7 @@
          resyntax/default-recommendations/mutability-predicates
          resyntax/default-recommendations/numeric-shortcuts
          resyntax/default-recommendations/require-and-provide-suggestions
+         resyntax/default-recommendations/simplify-named-let-initialization
          resyntax/default-recommendations/string-shortcuts
          resyntax/default-recommendations/syntax-parse-shortcuts
          resyntax/default-recommendations/syntax-rules-shortcuts
@@ -129,6 +131,7 @@
             numeric-shortcuts
             provide-contract-migration
             require-and-provide-suggestions
+            simplify-named-let-initialization
             string-shortcuts
             syntax-shortcuts
             syntax-parse-shortcuts

default-recommendations/simplify-named-let-initialization-test.rkt

@@ -0,0 +1,52 @@
+#lang resyntax/test
+
+
+require: resyntax/default-recommendations simplify-named-let-initialization
+
+
+header:
+--------------------
+#lang racket
+(define (a) 1)
+(define (b) 2)
+(define (c) 3)
+--------------------
+
+test: "original code should be refactorable to new code"
+--------------------
+(define (f a b c)
+  (let loop ([x (+ 1 2 3)]
+             [y (if (a)
+                    (b)
+                    (c))])
+    (loop x y)))
+====================
+(define (f a b c)
+  (define init-y
+    (if (a)
+        (b)
+        (c)))
+  (let loop ([x (+ 1 2 3)]
+             [y init-y])
+    (loop x y)))
+--------------------
+
+
+no-change-test: "code not refactorable when side-effecting expression is present"
+--------------------
+(define (f a b c)
+  (let loop ([x (displayln "foo")]
+             [y (if (a)
+                    (b)
+                    (c))])
+    (loop x y)))
+--------------------
+
+
+no-change-test: "code not refactorable when all expressions are single-line"
+--------------------
+(define (f a b c)
+  (let loop ([x (+ 1 2 3)]
+             [y 42])
+    (loop x y)))
+--------------------

default-recommendations/simplify-named-let-initialization.rkt

@@ -0,0 +1,67 @@
+#lang racket/base
+
+
+(require racket/contract/base)
+
+
+(provide
+ (contract-out
+  [simplify-named-let-initialization refactoring-suite?]))
+
+
+(require racket/list
+         racket/syntax
+         resyntax/base
+         resyntax/default-recommendations/private/definition-context
+         resyntax/default-recommendations/private/pure-expression
+         resyntax/default-recommendations/private/syntax-lines
+         syntax/parse)
+
+
+;@----------------------------------------------------------------------------------------------------
+
+
+(define-definition-context-refactoring-rule simplify-named-let-initialization-rule
+  #:description
+  "Complex multi-line initialization expressions in named `let` loops can be extracted into `define`\
+ bindings to improve readability."
+  #:literals (let)
+  (~seq leading-body ...
+        (let loop-name:id ([binding-id:id binding-expr:expr] ...)
+          loop-body ...))
+
+  #:do [(define-values (bindings-to-extract remaining-bindings)
+          (for/fold ([extracted '()]
+                     [remaining '()])
+                    ([id (in-list (attribute binding-id))]
+                     [expr (in-list (attribute binding-expr))])
+            (if (multiline-syntax? expr)
+                (values (cons (list id expr) extracted)
+                        remaining)
+                (values extracted
+                        (cons (list id expr) remaining)))))]
+
+  ;; Check that at least one binding expression is multi-line
+  #:when (not (null? bindings-to-extract))
+
+  ;; Check that all non-multi-line (remaining) binding expressions are pure
+  ;; (so we can safely reorder by extracting the multi-line ones)
+  #:when (for/and ([binding (in-list remaining-bindings)])
+           (syntax-parse (cadr binding)
+             [:pure-expression #true]
+             [_ #false]))
+
+  #:with ((extracted-id extracted-expr) ...) (reverse bindings-to-extract)
+  #:with ((kept-id kept-expr) ...) (reverse remaining-bindings)
+  #:with (init-id ...) (for/list ([id (in-list (attribute extracted-id))])
+                         (format-id id "init-~a" id))
+
+  (leading-body ...
+   (define init-id extracted-expr) ...
+   (let loop-name ([kept-id kept-expr] ...
+                   [extracted-id init-id] ...)
+     loop-body ...)))
+
+
+(define-refactoring-suite simplify-named-let-initialization
+  #:rules (simplify-named-let-initialization-rule))