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<< Style uniformity is more important than style itself >>
(Kernigan & Pike, The Practice of Programming)
OCaml Style:
- Spacing and indentation
- indent your code (using tuareg default)
- no strong constraints in formatting "let in"; possible styles are:
"let x = ... in"
"let x =
... in"
"let
x = ...
in"
- but: no extra indentation before a "in" coming on next line,
otherwise, it first shifts further and further on the right,
reducing the amount of space available; second, it is not robust to
insertion of a new "let"
- it is established usage to have space around "|" as in
"match c with
| [] | [a] -> ...
| a::b::l -> ..."
- in a one-line "match", it is preferred to have no "|" in front of
the first case (this saves spaces for the match to hold in the line)
- from about 8.2, the tendency is to use the following format which
limit excessive indentation while providing an interesting "block" aspect
type t =
| A
| B of machin
let f expr = match expr with
| A -> ...
| B x -> ...
let f expr = function
| A -> ...
| B x -> ...
- add spaces around = and == (make the code "breaths")
- the common usage is to write "let x,y = ... in ..." rather than
"let (x,y) = ... in ..."
- parenthesizing with either "(" and ")" or with "begin" and "end" is
common practice
- preferred layout for conditionals:
if condition then
premier-cas
else
deuxieme-cas
- in case of effects in branches, use "begin ... end" rather than
parentheses
if condition then begin
instr1;
instr2
end else begin
instr3;
instr4
end
- if the first branch raises an exception, avoid the "else", i.e.:
if condition then if condition then error "foo";
error "foo" -----> bar
else
bar
- it is the usage not to use ;; to end OCaml sentences (however,
inserting ";;" can be useful for debugging syntax errors crossing
the boundary of functions)
- relevant options in tuareg:
(setq tuareg-in-indent 2)
(setq tuareg-with-indent 0)
(setq tuareg-function-indent 0)
(setq tuareg-let-always-indent nil)
- Coding methodology
- no "try ... with _ -> ..." which catches even Sys.Break (Ctrl-C),
Out_of_memory, Stack_overflow, etc.
at least, use "try with e when Errors.noncritical e -> ..."
(to be detailed, Pierre L. ?)
- do not abuse of fancy combinators: sometimes what a "let rec" loop
does is more readable and simpler to grasp than what a "fold" does
- do not break abstractions: if an internal property is hidden
behind an interface, do no rely on it in code which uses this
interface (e.g. do not use List.map thinking it is left-to-right,
use map_left)
- in particular, do not use "=" on abstract types: there is no
reason a priori that it is the intended equality on this type; use the
"equal" function normally provided with the abstract type
- avoid polymorphically typed "=" whose implementation is not
optimized in OCaml and which has moreover no reason to be the
intended implementation of the equality when it comes to be
instantiated on a particular type (e.g. use List.mem_f,
List.assoc_f, rather than List.mem, List.assoc, etc, unless it is
absolutely clear that "=" will implement the intended equality, and
with the right complexity)
- any new general-purpose enough combinator on list should be put in
cList.ml, on type option in cOpt.ml, etc.
- unless of a good reason not to so, follow the style of the
surrounding code in the same file as much as possible,
the general guidelines are otherwise "let spacing breaths" (we
have large screen nowadays), "make your code easy to read and
to understand"
- document what is tricky, but do not overdocument, sometimes the
choice of names and the structuration of the code is a better
documentation than a long discourse; use of unicode in comments is
welcome if it can make comments more readable (then
"toggle-enable-multibyte-characters" can help when using the
debugger in emacs)
- all of initial "open File", or of small-scope File.(...), or
per-ident File.foo are common practices
- Choice of variable names
- be consistent when naming from one function to another
- be consistent with the naming adopted in the functions from the
same file, or with the naming used elsewhere by similar functions
- use variable names which express meaning
- keep "cst" for constants and avoid it for constructors which is
otherwise a source of confusion
- for constructors, use "cstr" in type constructor (resp. "cstru" in
constructor puniverse); avoid "constr" for "constructor" which
could be think as the name of an arbitrary Constr.t
- for inductive types, use "ind" in the type inductive (resp "indu"
in inductive puniverse)
- for env, use "env"
- for evar_map, use "sigma", with tolerance into "evm" and "evd"
- for named_context or rel_context, use "ctxt" or "ctx" (or "sign")
- for formal/actual indices of inductive types: "realdecls", "realargs"
- for formal/actual parameters of inductive types: "paramdecls", "paramargs"
- for terms, use e.g. c, b, a, ...
- if a term is known to be a function: f, ...
- if a term is known to be a type: t, u, typ, ...
- for a declaration, use d or "decl"
- for errors, exceptions, use e
- Common OCaml pitfalls
- in "match ... with Case1 -> try ... with ... -> ... | Case2 -> ...", or in
"match ... with Case1 -> match ... with SubCase -> ... | Case2 -> ...", or in
parentheses are needed around the "try" and the inner "match"
- even if stream are lazy, the Pp.(++) combinator is strict and
forces the evaluation of its arguments (use a "lazy" or a "fun () ->")
to make it lazy explicitly
- in "if ... then ... else ... ++ ...", the default parenthesizing
is somehow counter-intuitive; use "(if ... then ... else ...) ++ ..."
- in "let myspecialfun = mygenericfun args", be sure that it does no
do side-effect; prefer otherwise "let mygenericfun arg =
mygenericfun args arg" to ensure that the function is evaluated at
runtime
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