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Date: Tue, 17 Nov 2015 08:43:19 -0800 (PST)
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Subject: Re: Haskell, anyone?
From: Hadrien Grasland <hadrien.grasland@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:28420
Date: 2015-11-17T08:43:19-08:00
List-Id: <comp.lang.ada>

Le mardi 17 novembre 2015 13:01:24 UTC+1, G.B. a =E9crit=A0:
> > the horrors of recursion
>=20
> Recursion, I speculate, is one of the two things that
> a programmer new to FP style needs to learn, the other
> being combinatorial control of the evaluator's mechanics.
> It is like learning how to write assembly programming,
> with one difference: the "paper" is turned by 90=B0
> and FP is a little less explicit about instructing the
> machine.(*)

I would say that recursion is the goto statement of functional programming =
languages : necessary in order to achieve Turing-completeness, and occasion=
ally useful, but makes control flow messy and programs very difficult to re=
ason about, and should thus only be used in situations where no higher-leve=
l abstraction will fit.

The recursive hoops that one has to jump through in order to "modify" a com=
plex data structure are especially gruesome. Just implemented a radix tree =
in OCaml today, as an exercise, and the insertion function gave me a glimps=
e of what FP hell looks like. Sometimes, immutability can really make thing=
s much worse.

I enthusiastically approve of the creative uses that FP languages find to d=
iscriminated types, though. It gives me plenty of ideas to experiment with =
in my future Ada programs.