package batteries

The format to use for displaying the various arguments passed to the function.

Syntactically, the format is a character string which contains two types of objects: plain characters, which are simply copied, and directives, each of which causes the conversion and printing of arguments.

Simple directives

All directives start with the % character. In their simplest form, a directive is % followed by exactly one character:

• %d, %i, %n, %l, %L, or %N: convert an integer argument to signed decimal.
• %u: convert an integer argument to unsigned decimal.
• %x: convert an integer argument to unsigned hexadecimal, using lowercase letters.
• %X: convert an integer argument to unsigned hexadecimal, using uppercase letters.
• %o: convert an integer argument to unsigned octal.
• %s: insert a string argument.
• %S: insert a string argument in OCaml syntax (double quotes, escapes).
• %c: insert a character argument.
• %C: insert a character argument in OCaml syntax (single quotes, escapes).
• %f: convert a floating-point argument to decimal notation, in the style dddd.ddd.
• %F: convert a floating-point argument to OCaml syntax (dddd. or dddd.ddd or d.ddd e+-dd).
• %e or %E: convert a floating-point argument to decimal notation, in the style d.ddd e+-dd (mantissa and exponent).
• %g or %G: convert a floating-point argument to decimal notation, in style %f or %e, E (whichever is more compact).
• %B: convert a boolean argument to the string true or false
• %b: convert a boolean argument (for backward compatibility; do not use in new programs).
• %ld, %li, %lu, %lx, %lX, %lo: convert an int32 argument to the format specified by the second letter (decimal, hexadecimal, etc).
• %nd, %ni, %nu, %nx, %nX, %no: convert a nativeint argument to the format specified by the second letter.
• %Ld, %Li, %Lu, %Lx, %LX, %Lo: convert an int64 argument to the format specified by the second letter.
• !: take no argument and flush the output.
• %: take no argument and output one % character.
• ,: the no-op delimiter for conversion specifications

Unparsers

• %a: user-defined printer. Typically, this printer corresponds to two arguments: a printing function f, with type 'a output -> 'c -> unit and the item x you want to print, with type 'c. Item x will be printing by calling f out x, where out is the output you are currently using -- if you are calling printf, this output is the standard output (i.e. the screen), if you are calling eprintf, this will be the error channel, if you are calling fprintf, this will be the output you provided yourself, etc. More generally, if your Format has type ('a, 'b, 'd) format or ('a, 'b, 'd, 'e) format4, the printing function f must have type 'b -> 'c -> 'd, where x has type 'd.
• %t: same as %a but takes only a printing function f, without an item. If your Format has type ('a, 'b, 'd) format or ('a, 'b, 'd, 'e) format4, function f must have type 'b -> 'd.

Formatting formats

• %\{ fmt %\}: convert a Format to a string. The format argument must have the same type as the internal format string fmt. In other words, printf "%\{ %s %\}" accepts an argument whose type must be the same as that of format "%s", and prints that format argument as if it were a character string.
• %( fmt %): format string substitution. Takes a format string argument and substitutes it to the internal format string fmt to print following arguments. The argument must have the same type as fmt. printf "%\{ %s %\}" accepts an argument whose type must be the same as that of format "%s", and uses that argument to print the following arguments.

Additional options

The general format of directives is

% [flags] [width] [.precision] type

type is one of d, i, n, l, L, N, u, x ..., ( fmt %) and behaves as explained above.

The optional flags are:

• -: left-justify the output (default is right justification).
• 0: for numerical conversions, pad with zeroes instead of spaces.
• +: for numerical conversions, prefix number with a + sign if positive.
• space: for numerical conversions, prefix number with a space if positive.
• #: request an alternate formatting style for numbers.

The optional width is an integer indicating the minimal width of the result. For instance, %6d prints an integer, prefixing it with spaces to fill at least 6 characters.

The optional precision is a dot . followed by an integer indicating how many digits follow the decimal point in the %f, %e, and %E conversions. For instance, %.4f prints a float with 4 fractional digits.

The integer in a width or precision can also be specified as *, in which case an extra integer argument is taken to specify the corresponding width or precision. This integer argument precedes immediately the argument to print. For instance, %.*f prints a float with as many fractional digits as the value of the argument given before the float.

The usual printf function, prints to the standard output stdout, i.e. normally to the screen. If you are lost, this is probably the function you're looking for.

The usual eprintf function, prints to the standard error output stderr, used to display warnings and errors. Otherwise identical to printf.

A function which doesn't print its result but returns it as a string. Useful for building messages, for translation purposes or for display in a window, for instance.

While this function is quite convenient, don't abuse it to create very large strings such as files, that's not its role. For this kind of usage, prefer the more modular and usually faster fprintf.

Note that any function called with %a should return strings, i.e. should have type unit -> string.

A function which doesn't print its result but returns it as a string. Useful for building messages, for translation purposes or for display in a window, for instance.

While this function is quite convenient, don't abuse it to create very large strings such as files, that's not its role. For this kind of usage, prefer the more modular and usually faster fprintf. Note that any function called with %a should be able to print its result, i.e. should have type 'b output -> unit.

Warning: a partial application of this function can only be used once, because the BatInnerIO.output that it uses is closed afterwards. Example: let f = sprintf2 "%a" Int.print in [f 1; f 2] will fail.

General function. This function prints to any output. Typically, if you are attempting to build a large output such as a file, this is probably the function you are looking for. If you are writing a pretty-printer, this is probably the function you are looking for. If you are you are looking for a function to use for argument %a with printf, eprintf, sprintf2, ifprintf, bprintf2, kfprintf, ksprintf2, kbprintf2 or any other function with type (_, _ output, unit) format or (_, _ output, unit, _) format4, this is also probably the function you are looking for.

As fprintf but doesn't actually print anything. Sometimes useful for debugging.

As fprintf, but with buffers instead of outputs. In particular, any unparser called with %a should write to a buffer rather than to an output

As printf but writes to a buffer instead of printing to the output. By opposition to bprintf, only the result is changed with respect to printf, not the inner workings.

Same as fprintf, but instead of returning immediately, passes the output to its first argument at the end of printing.

Same as sprintf above, but instead of returning the string, passes it to the first argument.

Same as sprintf2 above, but instead of returning the string, passes it to the first argument.

Same as bprintf, but instead of returning immediately, passes the buffer to its first argument at the end of printing.

Same as bprintf2, but instead of returning immediately, passes the buffer to its first argument at the end of printing.

• deprecated

  This is a deprecated synonym for ksprintf.