parsing.md

Parsing

Implementations must act as if they used the following algorithm to parse POSIX-compliant dotenv files.

The input to the parsing stage is a sequence of tokens from the tokenization stage.

The output of the parsing stage is the result of parsing an assignment list.

Definitions

Next token

The next token is the first token in the input token sequence that has not yet been consumed. Initially, the next token is the first token in the input token sequence.

Current token

The current token is the last token to have been consumed.

Parsing algorithm

Parsing an assignment list

• Let node-list be a new empty list.
• Consume the next token.
• loop:
  • Switch on the current token:
    • EOF:
      • return node-list.
    • Assign:
      • let node be the result of parsing an assignment.
      • append node to node-list.
    • anything else:
      • Parse error.

Parsing an assignment

• Create a new Assignment node.
• set the node's name attribute to the current token's value.
• set the node's value attribute to the result of parsing an assignment value.
• return the node.

Parsing an assignment value

• Let node-list be a new empty list.
• loop:
  • Consume the next token.
    • EOF, Assign:
      • return node-list.
    • Characters:
      • Create a new Characters node.
      • set the node's value attribute to the current token's value.
      • append the newly created node to node-list.
    • SimpleExpansion:
      • Create a new Expansion node.
      • set the node's name attribute to the current token's value.
      • set the node's operator attribute to - (U+002D HYPHEN-MINUS).
      • set the node's value attribute to an empty list.
      • append the newly created node to node-list.
    • StartExpansion:
      • Create a new Expansion node.
      • set the node's name attribute to the current token's value.
      • set the node's operator attribute to the result of parsing an expansion operator.
      • set the node's value attribute to the result of parsing an expansion value.
      • append the newly created node to node-list.
    • anything else:
      • Parse error.

Parsing an expansion operator

Consume the next token.

• ExpansionOperator:
  • return the current token's value.
• anything else:
  • Parse error.

Parsing an expansion value

• Let node-list be a new empty list.
• loop:
  • Consume the next token.
    • EndExpansion:
      • return node-list.
    • Characters:
      • Create a new Characters node.
      • set the node's value attribute to the current token's value.
      • append the newly created node to node-list.
    • SimpleExpansion:
      • Create a new Expansion node.
      • set the node's name attribute to the current token's value.
      • set the node's operator attribute to - (U+002D HYPHEN-MINUS).
      • set the node's value attribute to an empty list.
      • append the newly created node to node-list.
    • StartExpansion:
      • Create a new Expansion node.
      • set the node's name attribute to the current token's value.
      • set the node's operator attribute to the result of parsing an expansion operator.
      • set the node's value attribute to the result of parsing an expansion value.
      • append the newly created node to node-list.
    • anything else:
      • Parse error.