2 Notation
Shplait syntax is based on shrubbery syntax, which is described at Shrubbery Notation. Superficially, Shplait resembles Rhombus, which also uses shrubbery notation, but Shplait is statically typed, much smaller, and has a different set of constructs overall.
Shrubbery notation defines the syntax of identifiers and numbers, and it defines how token sequences are grouped by parentheses, brackets, braces, quotes, and indentation. We define Shplait using patterns over Shrubbery forms.
In the pattern form a syntactic form, ... indicates zero or more repetitions of the preceding form. The preceding form can be an individual term, a group, or an alternative. (Words like term, group, and alternative are defined as part of the specification of shrubbery notation.)
id (or a name that ends in id) stands for an identifier, such as x or interp.
op (or a name that ends in op) stands for an operator, such as + or ==.
expr (or a name that ends in ...) stands for an expression, such as x, "hello", 1 + 2, or f(3, 4).
defn stands for a definition, such as def x = 1 or fun f(x): x.
body stands for a sequence of definitions and expressions that ends with an expression, and where an expression that isn’t the ending expression must have type Void; see also block. The last expression in body provides the type and result value of the body sequence.
typed_id stands for either an identifier or an identifier followed by :: and a declared type. Note that there cannot be spaces between the two :s in ::.