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put_char/1

Module​

Built-in predicate.

Description​

Writes Char to the current output stream.

Signature​

put_char(+Char) is det

Examples​

Write a single character to user output​

This scenario demonstrates using put_char/1 to write a single character to the current output stream. The character appears in the user_output field of the response.

Here are the steps of the scenario:

  • Given the module configuration:
{
  "limits": {
    "max_user_output_size": 10
  }
}
  • Given the query:
put_char('b').
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 3986
answer:
  has_more: false
  variables:
  results:
  - substitutions:
user_output: "b"

Write multiple characters to user output​

This scenario demonstrates chaining multiple put_char/1 calls to write several characters. Each character is appended to the user output stream.

Here are the steps of the scenario:

  • Given the module configuration:
{
  "limits": {
    "max_user_output_size": 10
  }
}
  • Given the query:
put_char('a'), put_char('b'), put_char('c').
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 4042
answer:
  has_more: false
  variables:
  results:
  - substitutions:
user_output: "abc"

Write characters with user output size limit​

This scenario shows how the user output is truncated when it exceeds the configured max_user_output_size limit. The limit is measured in bytes, so only the last bytes that fit within the limit are kept.

Here are the steps of the scenario:

  • Given the module configuration:
{
  "limits": {
    "max_user_output_size": 3
  }
}
  • Given the query:
put_char('h'), put_char('e'), put_char('l'), put_char('l'), put_char('o').
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 4098
answer:
  has_more: false
  variables:
  results:
  - substitutions:
user_output: "llo"

Write UTF-8 character​

This scenario illustrates writing UTF-8 characters using put_char/1. Multi-byte characters like emojis occupy more space in the buffer.

Here are the steps of the scenario:

  • Given the module configuration:
{
  "limits": {
    "max_user_output_size": 10
  }
}
  • Given the program:
log_message([]).
log_message([H|T]) :-
    put_char(H),
    log_message(T).
  • Given the query:
log_message("😀").
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 4093
answer:
  has_more: false
  variables:
  results:
  - substitutions:
user_output: "😀"