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Aladino Language

Aladino is a simple language to specify steps in pull request workflows.

The expressions in the language allow you to easily perform read and write actions on pull requests.

Syntax​

The syntax of Aladino is quite simple. Here's the BNF grammar representation:

prog := stat_list

stat := expr

expr := expr BINOP expr
    | UNARYOP expr
    | TIMESTAMP
    | RELATIVE_TIMESTAMP
    | NUMBER
    | STRING
    | BOOLEAN
    | '(' expr ')'
    | '[' expr_list ']'
    | '$' IDENTIFIER '(' expr_list ')'
    | '(' expr_list '=>' expr  ')'

expr_list :=
        expr ',' expr_list
    | expr
    |

TIMESTAMP :=
        YYYYMMDD
    | YYYY-MM-DD
    | YYYYMMDDTHH:MM:SS
    | YYYY-MM-DDTHH:MM:SS

RELATIVE_TIMESTAMP := NUMBER TIME_UNIT ago

TIME_UNIT :=
        'year'   | 'years'
    | 'month'  | 'months'
    | 'week'   | 'weeks'
    | 'day'    | 'days'
    | 'hour'   | 'hours'
    | 'minute' | 'minutes'

BINOP :=
        '==' | '>=' | '>' | '<' | '<='
    | '&&' | '||'

UNARYOP := '!'

This allows us to specify:

  1. Logical expressions: e.g. "a" == "a" or $fun() == 1;
  2. Function calls: e.g. $label("bug")
  3. Lambda functions: e.g. ($dev => $dev == $getAuthor())

Semantic​

Aladino supports five types of values: booleans, numbers, strings, arrays and a special type _action_.

Since the language is quite simple, it is also straightforward to perform type inference.

There are two requirements when it comes to typing:

  1. The type of the expression in a rule spec is bool. For example, the following rule is invalid:
- name: doesnt-type-check-to-bool
  kind: patch
  description: Rule that does not type check to bool
  spec: "hello" # type error
  1. The type of each action to be effect. For example, the following workflow is invalid because of its actions:
- name: invalid-workflow
  description: Invalid workflow because of action
  run:
    if: rule_1
    then: "hello" # type error

Since, by design, you cannot define functions or variables, the usefulness of the language comes down to the set of built-in variables and functions that are provided.