source | all docs for version 0.8.12 | all versions | oilshell.org

Warning: Work in progress! Leave feedback on Zulip or Github if you'd like this doc to be updated.

Oil Expressions vs. Python

Oil's expression language borrows heavily from Python.

In fact, it literally started with Python's Grammar/Grammar file.

Literal Syntax

• String literals are like shell string literals.
  • Single quoted - r'c:\Program Files\' or $'line\n'.
  • Double Quoted
  • \u{3bc} instead of \uhhhh and \UHHHHHHHH
• Dicts: come from JavaScript, with unquoted keys, and "punning".
• lists, ints, floats: the same
• Tuples (TODO):
  • Singleton tuples like 42, are disallowed, in favor of the more explicit tup(42).

New Literals

• Lists with unquoted words: %(one two three)
• %symbol (used in eggex now, but could also be used as interned strings)
• Raw character literals like \n and \u{03bc}, and also #'a'
• Block ^(ls | wc -l)
• Unevaluated expression: ^[1 +a[i] + f(x)]

Operators

Kinds of of operators:

• Equality === ~== in not in
• Comparison < > <= =>
• Arithmetic + -
• Bitwise & |
• Logical and or
• Ternary
• Indexing and Slicing
• Function Call
• Other: ++
• Oil sigils: $ and @

Equality:

• === for exact quality?
• ~== for approximate (numbers and strings)
  • maybe there is no ==?

Oil doesn't overload operators as much, and does string <-> int conversion:

• a + b is for addition, while a ++ b is for concatenation.
• a < b does numeric comparison (with conversion). cmp() could be for strings.

No "accidentally quadratic"

• No in for array/list membership. Only dict membership.
• The ++= operator on strings doesn't exist

Other:

• I removed the 1:5:2 syntax because 0::2 conflicts with module::name. This might have been unnecessary.
• Egg expressions and the ~ operator rather than the re module.
• The ~~ glob match operator

New Operators

• mydict->key as an alias for mydict['key']
• ++ mentioned above

Semantic Differences

• Iterating over a string yields code points, not one-character strings.
  • s[i] returns an integer code point ("rune").
  • TODO: maybe this should be runeAt() and byteAt()?

Related Links

• Issue 835: Make expression language compatible with Python