README.md — sigil-transducers

1# sigil-transducers

Composable transducer library for Sigil. Provides polymorphic sequence operations and transducer pipelines that work across lists, vectors, arrays, and dicts.

5## Installation

7Add to your `package.sgl` dependencies:

9```scheme

10(from-git url: "codeberg:sigil/sigil-transducers")

11```

13## Usage

15### Polymorphic Operations

17When imported, `(sigil seq)` provides polymorphic versions of common operations that work on any collection type:

19```scheme

20(import (sigil seq))

22(map square '(1 2 3)) ; => (1 4 9)

23(map square #(1 2 3)) ; => #(1 4 9)

24(filter even? '(1 2 3 4)) ; => (2 4)

25(filter even? #(1 2 3 4)) ; => #(2 4)

26(fold + 0 '(1 2 3 4)) ; => 10

27(any even? '(1 3 4 5)) ; => #t

28(every even? '(2 4 6)) ; => #t

29(find even? '(1 3 4 5)) ; => 4

30```

32### Transducers

34Transducers are composable transformation pipelines that separate *what* to transform from *how* to iterate:

36```scheme

37(import (sigil seq))

39(define xform

40 (comp (filtering even?)

41 (mapping square)

42 (taking 5)))

44(transduce xform conj '() (iota 100)) ; => (0 4 16 36 64)

45```

47### Transducer Constructors

49- `(mapping f)` - Transform each element by applying `f`

50- `(filtering pred)` - Keep only elements satisfying `pred`

51- `(taking n)` - Take at most `n` elements, then stop

52- `(dropping n)` - Skip the first `n` elements

53- `(taking-while pred)` - Take elements while `pred` is true

54- `(dropping-while pred)` - Drop elements while `pred` is true

55- `cat` - Flatten one level of nesting

56- `(mapcat f)` - Map then concatenate

58### Composition

60Compose transducers left-to-right with `comp`:

62```scheme

63(comp (filtering even?) (mapping square) (taking 3))

64```

66### Execution

- `(transduce xform rf init coll)` - Apply transducer `xform` with reducing function `rf`, initial value `init`, over collection `coll`

69- `(into to xform from)` - Transform and collect into a collection of the same type as `to`

70- `(sequence xform coll)` - Transform a collection, preserving its type

72### Reducers

74- `conj` - Build lists (via cons)

75- `conj-vec` - Build vectors (builds list, convert with `into`)

76- `conj-dict` - Build dicts from `(key . value)` pairs

78### Stream Processing

80Transducers also work for processing channel message streams:

82```scheme

83(import (sigil seq)

84 (sigil channels)

85 (sigil async))

87(define log-xform

88 (comp (filtering (lambda (msg) (equal? (dict-ref msg level:) "error")))

89 (mapping (lambda (msg) (dict-ref msg text:)))))

91(with-async

92 (go (for-each (lambda (msg) (channel-send logs msg)) messages)

93 (channel-close! logs))

94 (go (for-channel (msg logs)

95 (let ((xrf (log-xform (lambda (acc x) (println "ERROR: ~a" x) acc))))

96 (xrf #f msg)))))

97```

99## License

100

101BSD-3-Clause