parens mean application
in math
- parens mean grouping
- so (1 + 2) = 1 + 2
- same in many programming langs
in scheme
- parens mean application
- (+ 3 4) applies plus to 3 and 4
- (7) applies 7 to nothing, and fails
- ((+ 3 4)) therefore fails too
how many exprs?
- parens turn a sequence of exprs into one expr
- “(+ 3 4)” is one expression
- “+ 3 4” is three expressions