lfe_io(3)

okay bestie, welcome to lfe_io(3) from the Library Functions Manual ✨ — this is the LFE io module, and it’s here to make input/output feel like a whole vibe, not a chore. Let’s get into it 💅

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🌸 NAME 🌸

lfe_io — Lisp Flavoured Erlang (LFE) io functions 🫶

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✨ SYNOPSIS ✨

This module provides a standard set of io functions for LFE. In the following description, many functions have an optional parameter IoDevice. If included, it must be the pid of a process which handles the IO protocols such as the IoDevice returned by file:open/2.

Two functions in this module are used to generate aesthetically attractive representations of abstract forms, which are suitable for printing. These functions return (possibly deep) lists of characters and generate an error if the form is wrong.

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🎀 DATA TYPES 🎀

chars() = [char() | chars()]

prompt() = atom() | unicode:chardata()

filesexpr() = {Sexpr,Line}

The filesexpr() format is what lfe_io:parse_file/1 returns, and it’s used by the compiler to give better error information. Cute and useful? We love that for us 💖

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💅 EXPORTS 💅

Here’s the whole export lineup, bestie — no skips, no cuts ✨

get_line

get_line() -> Data | {error, ErrorInfo} | eof

get_line(Prompt) -> Data | {error, ErrorInfo} | eof

get_line(IoDevice, Prompt) -> Data | {error, ErrorInfo} | eof

Reads a line from the standard input (IoDevice), prompting it with prompt (Prompt). Note that this call guarantees that the input is saved in the input history. Iconic little guarantee, honestly 🎀

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read

read() -> {ok, Sexpr} | {error, ErrorInfo} | eof

read(Prompt) -> {ok, Sexpr} | {error, ErrorInfo} | eof

read(IoDevice, Prompt) -> {ok, Sexpr} | {error, ErrorInfo} | eof

Read an s-expr from the standard input (IoDevice) with a prompt (Prompt). Note that this is not line-oriented in that it stops as soon as it has consumed enough characters. It’s giving “I know what I need, thanks” energy 💅

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read_line

read_line() -> {ok, Sexpr} | {error, ErrorInfo} | eof

read_line(Prompt) -> {ok, Sexpr} | {error, ErrorInfo} | eof

read_line(IoDevice, Prompt) -> {ok, Sexpr} | {error, ErrorInfo} | eof

Read the first s-expr from the standard input (IoDevice) with a prompt (Prompt). Note that this is line-oriented in that it reads whole lines, discarding left-over characters in the last line. Very “finish your plate” of it 🍓

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read_string

read_string(String) -> {ok, [Sexpr]} | {error, ErrorInfo}

Read all the s-exprs from String. Slay, string goblin 🌈

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print and print1

print(Sexpr) -> ok

print(IoDevice, Sexpr) -> ok

Print the s-expr Sexpr to the standard output (IoDevice).

print1(Sexpr) -> DeepCharList

Return the list of characters which represent the s-expr Sexpr.

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prettyprint and prettyprint1

prettyprint(Sexpr) -> ok

prettyprint(IoDevice, Sexpr) -> ok

Pretty print the s-expr Sexpr to the standard output (IoDevice). It’s the same s-expr, but with main character energy ✨

prettyprint1(Sexpr) -> DeepCharList

prettyprint1(Sexpr, Depth) -> DeepCharList

prettyprint1(Sexpr, Depth, Indentation) -> DeepCharList

prettyprint1(Sexpr, Depth, Indentation, LineLength) -> DeepCharList

Return the list of characters which represents the prettyprinted s-expr Sexpr. The default for Depth is 30, Indentation is 0, and LineLength is 80. Defaults understood, bestie 🫶

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format, fwrite, format1 and fwrite1

format(Format, Args) -> ok

format(IoDevice, Format, Args) -> ok

fwrite(Format, Args) -> ok

fwrite(IoDevice, Format, Args) -> ok

Print formatted output. The following commands are valid in the format string:

• ~w, ~W — print LFE terms
• ~p, ~P — prettyprint LFE terms
• ~s — print a string
• ~e, ~f, ~g — print floats
• ~b, ~B — based integers
• ~x, ~X — based integers with a prefix
• ~+, ~# — based integers in vanilla erlang format
• ~~ — prints ~
• ~c, ~n, ~i

Currently they behave as for vanilla erlang except that ~w, ~W, ~p, ~P print the terms as LFE sexprs. Periodt 💅

format1(Format, Args) -> DeepCharList

fwrite1(Format, Args) -> DeepCharList

Return the formatted output with same arguments as format/fwrite.

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read_file

read_file(FileName|Fd) -> {ok,[Sexpr]} | {error,ErrorInfo}

read_file(FileName|Fd, Line) -> {ok, [Sexpr]} | {error, ErrorInfo}

Read the file Filename or the already opened file’s file descriptor Fd, returning a list of s-exprs. File-reading fairy vibes 🧚

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parse_file

parse_file(FileName|Fd) -> {ok, [FileSexpr]} | {error, ErrorInfo}

parse_file(FileName|Fd, Line) -> {ok, [FileSexpr]} | {error, ErrorInfo}

where

FileSexpr = filesexpr()

Read the file Filename or the already opened file’s file descriptor Fd, returning a list of pairs containing s-expr and line number of the start of the s-expr. The line numbers are giving “receipts included” 🔥

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scan_sexpr

scan_sexpr(Cont, Chars) -> {done, Ret, RestChars} | {more, Cont1}

scan_sexpr(Cont, Chars, Line) -> {done, Ret, RestChars} | {more, Cont1}

This is a re-entrant call which scans tokens from the input and returns a parsed s-expr. If there are enough characters to parse a sexpr or it detects an error then it returns {done,...}, otherwise it returns {more,Cont} where Cont is used in the next call to scan_sexpr with more characters to try and parse a sexpr. This is continued until a sexpr has been parsed. Cont is initially [].

It is not designed to be called directly by an application but used through the i/o system where it can typically be called in an application by:

io:request(In, {get_until,unicode,Prompt,Module,scan_sexpr,[Line]})

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🚨 ERROR INFORMATION 🚨

The ErrorInfo mentioned above is the standard ErrorInfo structure which is returned from all IO modules. It has the following format:

{ErrorLine, Module, ErrorDescriptor}

A string describing the error is obtained with the following call:

apply(Module, format_error, ErrorDescriptor)

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👑 AUTHORS 👑

• Robert Virding.

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okay that’s the whole page, bestie — the cute little footer says 2008-2024 and lfe_io(3), and honestly? iconic. mwah 💖