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write/1

Module​

Built-in predicate.

Description​

Writes Term to the current output stream.

Signature​

write(+Term) is det

Examples​

Write a simple atom to user output​

This scenario demonstrates using write/1 to write an atom to the current output stream. The term is written in human-readable form to the user_output field of the response.

Here are the steps of the scenario:

  • Given the module configuration:
{
  "limits": {
    "max_user_output_size": 20
  }
}
  • Given the query:
write(hello).
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 4002
answer:
  has_more: false
  variables:
  results:
  - substitutions:
user_output: "hello"

Write a string to user output​

This scenario demonstrates writing an atom containing spaces using write/1.

Here are the steps of the scenario:

  • Given the module configuration:
{
  "limits": {
    "max_user_output_size": 30
  }
}
  • Given the query:
write('hello world').
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 4010
answer:
  has_more: false
  variables:
  results:
  - substitutions:
user_output: "hello world"

Write multiple terms to user output​

This scenario demonstrates chaining multiple write/1 calls to output several terms. Each term is appended directly to the user output stream without spaces.

Here are the steps of the scenario:

  • Given the module configuration:
{
  "limits": {
    "max_user_output_size": 30
  }
}
  • Given the query:
write('hello'), write(' '), write('world'), write('!').
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 4134
answer:
  has_more: false
  variables:
  results:
  - substitutions:
user_output: "hello world!"

Write with user output size limit​

This scenario shows how write/1 respects the max_user_output_size limit. If the output exceeds the limit, only the last bytes that fit are retained.

Here are the steps of the scenario:

  • Given the module configuration:
{
  "limits": {
    "max_user_output_size": 5
  }
}
  • Given the query:
write('hello world'), put_char('!').
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 4038
answer:
  has_more: false
  variables:
  results:
  - substitutions:
user_output: "orld!"

Write numbers and complex terms​

This scenario demonstrates that write/1 can output numbers and complex terms.

Here are the steps of the scenario:

  • Given the module configuration:
{
  "limits": {
    "max_user_output_size": 30
  }
}
  • Given the query:
write(42), write(' '), write([1,2,3]).
  • 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: "42 [1,2,3]"

Combine write/1 and put_char/1 for formatted output​

This scenario shows how write/1 and put_char/1 work together to create formatted output, useful for debugging and logging in Prolog programs.

Here are the steps of the scenario:

  • Given the module configuration:
{
  "limits": {
    "max_user_output_size": 51
  }
}
  • Given the program:
log(Message) :- write('LOG: '), write(Message).
  • Given the query:
log('Starting query'), put_char('\n'),
log('Processing data'), put_char('\n'),
log('Done').
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 4324
answer:
  has_more: false
  variables:
  results:
  - substitutions:
user_output: |
  LOG: Starting query
  LOG: Processing data
  LOG: Done