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Oil Expressions vs. Python

Oil's expression language borrows heavily from Python. In fact, it literally started with Python's Grammar/Grammar file.

This doc describes some differences, which may help Python users learn Oil.

If you don't know Python, see A Tour of the Oil Language.

Table of Contents

Literals for Data Types

String literals are like shell string literals, not like Python.
- Single quoted - r'c:\Program Files\' or $'line\n'.
- Double Quoted
- Unicode literals are \u{3bc} instead of \u03bc and \U000003bc
Dicts: come from JavaScript, with unquoted keys, and "punning".
Lists: In addition to Python-like literals ['pea', 'nut'], there are shell-like literals %(pea nut).
Booleans / null: true, false, and null are preferred, but True, False, and None are accepted for compatibility.
Tuples (TODO): Does Oil have true tuples?
- Singleton tuples like 42, are disallowed, in favor of the more explicit tup(42).

Other literals like ints and floats are the same as in Python.

%symbol (used in eggex now, but could also be used as interned strings)
Raw character literals like \n and \u{03bc}, and also #'a'
Unevaluated expressions
- Block ^(ls | wc -l)
- Unevaluated expression: ^[1 + a[i] + f(x)]
- Arg list: ^{42, verbose = true}

Kinds of of operators:

Equality:

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.

Other:

I removed the 1:5:2 syntax because 0::2 conflicts with module::name. This might have been unnecessary.

mydict->key as an alias for mydict['key']
++ mentioned above
Pattern Matching
- Egg expressions and the ~ operator rather than the re module.
- The ~~ glob match operator

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()?
No "accidentally quadratic"
- No in for array/list membership. Only dict membership.
- The ++= operator on strings doesn't exist
Bools and integers are totally separate types. Oil is like JavaScript, where they aren't equal: true !== 1. In Python, they are equal: True == 1.