picos

Input / Output IO

Here is the truth about I/O in PicoLisp: everything is a stream or a list of characters, and the same functions that print to your terminal can print into a socket, a file or a string. Once you meet in, out and prin, the rest is composition.

What it is, in plain words

PicoLisp I/O is built from a few ideas:

Current input / output – redirected with in and out for the dynamic extent of a body.
Characters and lines – char, line, read, skip.
Printing – prin, prinl, print, println, space, pack.
Files and processes – pathnames, pipe, HTTP via @lib/http.l.
Binary – rd, wr for raw bytes when text isn’t enough.

There is no separate “file object” API to memorise – you bind the current stream and use the same readers and writers.

Why it matters

Web handlers, CGI, templating and DB dumps in PicoLisp are all I/O redirection plus printing. Understanding out/in means understanding how Pil apps talk to the world without a maze of classes.

An everyday analogy: a funnel you can aim

Instead of every tool having its own hose, PicoLisp gives you one funnel (prin) and lets you aim it at the sink, the bucket or the neighbour’s tank (out "file", out (pipe …), HTTP response). Same funnel, different target.

flowchart LR
  B[body of code] --> P[prin / print]
  P --> C[current output]
  O["(out target …)"] --> C

A hands-on example

# Write a file
(out "hello.txt"
   (prinl "Hello from Vikix")
   (println (date) (time)) )

# Read it back
(in "hello.txt"
   (until (eof)
      (println (line T)) ) )

# Capture into a string
(pack
   (list
      (print "x=" 3)
      (prin " ")
      (print "y=" 4) ) )

# Pipe
(in '(pipe (exec "uname" "-a"))
   (prinl (line T)) )

# HTTP server fragment (after loading http/xhtml)
(de go ()
   (html 0 "Hi" NIL NIL
      (<h1> "Hello")
      (<p> "Uptime thoughts go here") ) )

print produces a readable, read-able representation (with quotes); prin prints raw. Choose consciously – especially when emitting HTML (where @lib/xhtml.l helpers already escape).

Common misconceptions

"prin and print are synonyms." They differ on quoting and separators.
“You must close files.” in/out close when the body returns (even on throw).
“Binary needs a different language.” Use rd/wr and sizes.
“HTTP is separate.” It’s streams plus libraries.

Pretty-printing and debugging

(pretty Expr) and friends help you see structure. During HTTP development, temporarily (out 2 (println …)) to write traces to stderr without corrupting the response body. For large dumps, prefer writing files with out over flooding the console.

Remember that read reads one Pil expression – great for config files written as s-expressions, surprising if you expected line-oriented text (use line for that).

Connections

PicoLisp, PicoLisp Tutorials, Pil Box.
PicoLisp DB, with-output-to-string (CL cousin).

Comments can be embedded in the input stream with the hash # character. Everything up to the end of that line will be ignored by the reader.

: (* 1 2 3)  # This is a comment
-> 6

A comment spanning several lines (a block comment) may be enclosed between

#{ and }#