Add pipeline() function

toolz/curried/__init__.py

@@ -30,6 +30,7 @@
     comp,
     complement,
     compose,
+    compose_left,
     concat,
     concatv,
     count,

toolz/functoolz.py

@@ -10,8 +10,8 @@
 
 
 __all__ = ('identity', 'apply', 'thread_first', 'thread_last', 'memoize',
-           'compose', 'pipe', 'complement', 'juxt', 'do', 'curry', 'flip',
-           'excepts')
+           'compose', 'compose_left', 'pipe', 'complement', 'juxt', 'do',
+           'curry', 'flip', 'excepts')
 
 
 def identity(x):
@@ -537,6 +537,7 @@ def compose(*funcs):
     '4'
 
     See Also:
+        compose_left
         pipe
     """
     if not funcs:
@@ -547,6 +548,27 @@ def compose(*funcs):
         return Compose(funcs)
 
 
+def compose_left(*funcs):
+    """ Compose functions to operate in series.
+
+    Returns a function that applies other functions in sequence.
+
+    Functions are applied from left to right so that
+    ``compose_left(f, g, h)(x, y)`` is the same as ``h(g(f(x, y)))``.
+
+    If no arguments are provided, the identity function (f(x) = x) is returned.
+
+    >>> inc = lambda i: i + 1
+    >>> compose_left(inc, str)(3)
+    '4'
+
+    See Also:
+        compose
+        pipe
+    """
+    return compose(*reversed(funcs))
+
+
 def pipe(data, *funcs):
     """ Pipe a value through a sequence of functions
 

toolz/tests/test_functoolz.py

@@ -1,7 +1,8 @@
 import platform
 
 from toolz.functoolz import (thread_first, thread_last, memoize, curry,
-                             compose, pipe, complement, do, juxt, flip, excepts, apply)
+                             compose, compose_left, pipe, complement, do, juxt,
+                             flip, excepts, apply)
 from operator import add, mul, itemgetter
 from toolz.utils import raises
 from functools import partial
@@ -505,17 +506,54 @@ def _should_curry(self, args, kwargs, exc=None):
     """
 
 
-def test_compose():
-    assert compose()(0) == 0
-    assert compose(inc)(0) == 1
-    assert compose(double, inc)(0) == 2
-    assert compose(str, iseven, inc, double)(3) == "False"
-    assert compose(str, add)(1, 2) == '3'
+def generate_compose_test_cases():
+    """
+    Generate test cases for parametrized tests of the compose function.
+    """
 
-    def f(a, b, c=10):
+    def add_then_multiply(a, b, c=10):
         return (a + b) * c
 
-    assert compose(str, inc, f)(1, 2, c=3) == '10'
+    return (
+        (
+            (),        # arguments to compose()
+            (0,), {},  # positional and keyword args to the Composed object
+            0          # expected result
+        ),
+        (
+            (inc,),
+            (0,), {},
+            1
+        ),
+        (
+            (double, inc),
+            (0,), {},
+            2
+        ),
+        (
+            (str, iseven, inc, double),
+            (3,), {},
+            "False"
+        ),
+        (
+            (str, add),
+            (1, 2), {},
+            '3'
+        ),
+        (
+            (str, inc, add_then_multiply),
+            (1, 2), {"c": 3},
+            '10'
+        ),
+    )
+
+
+def test_compose():
+    for (compose_args, args, kw, expected) in generate_compose_test_cases():
+        assert compose(*compose_args)(*args, **kw) == expected
+
+
+def test_compose_metadata():
 
     # Define two functions with different names
     def f(a):
@@ -536,6 +574,25 @@ def g(a):
     assert composed.__doc__ == 'A composition of functions'
 
 
+def generate_compose_left_test_cases():
+    """
+    Generate test cases for parametrized tests of the compose function.
+
+    These are based on, and equivalent to, those produced by
+    enerate_compose_test_cases().
+    """
+    return tuple(
+        (tuple(reversed(compose_args)), args, kwargs, expected)
+        for (compose_args, args, kwargs, expected)
+        in generate_compose_test_cases()
+    )
+
+
+def test_compose_left():
+    for (compose_left_args, args, kw, expected) in generate_compose_left_test_cases():
+        assert compose_left(*compose_left_args)(*args, **kw) == expected
+
+
 def test_pipe():
     assert pipe(1, inc) == 2
     assert pipe(1, inc, inc) == 3