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cart.sx — cart as an ordered list of (sku variant qty) lines. Pure operations: cart-add (merge-or-append), cart-set-qty (0 removes), cart-remove, with cart-qty/count/skus/empty? accessors. cart-lineo exposes lines relationally via membero. Total 34/34. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
87 lines
2.3 KiB
Plaintext
87 lines
2.3 KiB
Plaintext
;; lib/commerce/cart.sx — cart as an ordered list of line items.
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;;
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;; A cart is a native list of lines; a line is (list sku variant qty).
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;; All operations are pure: they return a new cart, never mutate. Line
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;; order is insertion order (stable) so totals are reproducible.
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;;
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;; cart-lineo is the relational view — because a line *is* a (sku variant qty)
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;; tuple, membero queries the cart directly, forward or backward.
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(define empty-cart (list))
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(define make-line (fn (sku variant qty) (list sku variant qty)))
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(define line-sku (fn (l) (nth l 0)))
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(define line-variant (fn (l) (nth l 1)))
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(define line-qty (fn (l) (nth l 2)))
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(define
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same-line?
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(fn
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(l sku variant)
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(and (= (line-sku l) sku) (= (line-variant l) variant))))
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(define
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cart-qty
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(fn
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(cart sku variant)
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(let
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((m (filter (fn (l) (same-line? l sku variant)) cart)))
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(if (empty? m) 0 (line-qty (first m))))))
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(define
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cart-remove
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(fn
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(cart sku variant)
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(filter (fn (l) (not (same-line? l sku variant))) cart)))
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;; Add qty units; merges into an existing (sku,variant) line in place,
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;; otherwise appends a new line at the end.
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(define
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cart-add
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(fn
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(cart sku variant qty)
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(let
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((existing (cart-qty cart sku variant)))
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(if
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(= existing 0)
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(append cart (list (make-line sku variant qty)))
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(map
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(fn
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(l)
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(if
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(same-line? l sku variant)
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(make-line sku variant (+ existing qty))
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l))
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cart)))))
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;; Set the absolute quantity; qty <= 0 removes the line.
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(define
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cart-set-qty
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(fn
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(cart sku variant qty)
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(if
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(<= qty 0)
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(cart-remove cart sku variant)
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(if
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(= (cart-qty cart sku variant) 0)
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(append cart (list (make-line sku variant qty)))
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(map
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(fn
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(l)
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(if (same-line? l sku variant) (make-line sku variant qty) l))
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cart)))))
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(define cart-empty? (fn (cart) (empty? cart)))
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(define cart-lines (fn (cart) cart))
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(define cart-skus (fn (cart) (map line-sku cart)))
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;; Total number of units across all lines.
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(define
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cart-count
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(fn (cart) (reduce (fn (acc l) (+ acc (line-qty l))) 0 cart)))
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;; Relational view of cart lines.
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(define
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cart-lineo
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(fn (cart sku variant qty) (membero (list sku variant qty) cart)))
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