But, of course, you don't have to have code files full of parens in order to have s-expressions. Alternative syntaxes have never taken hold in the Lisp world, which may mean they just offer nothing to an experienced Lisp hacker, but they're certainly not impossible.
You can have user-definable infix operators; Haskell has them and uses them to good effect. (The way Haskell does it, you can't have identifiers composed of both letters and operator characters, which Lisp people like to do, but I think we can safely treat that as a matter of taste.) You pick a symbol, say ~, and assign it a precedence and left- or right-associativity:
infixr 3 ~
infixl 7 .!.
Now (x ~ y .!. z) is parsed as ((~) x ((.!.) y z)), where (~) is the Haskell way of making the ~ operator as a prefix function. Haskell also lets you use a prefix function as an infix operator, by putting backquotes around it.
If you want to apply this in Lisp, there is the issue that (foo) means something else than foo; I would like to allow (foo x + bar y) to mean ((+) (foo x) (bar y)), but I wouldn't want (x + y) to mean ((+) (x) (y)). My solution would be that a single value is parsed as just a value, but multiple values next to each other is a function call: (foo x + y) is ((+) (foo x) y), to call y without parameters you have to write (foo x + (y)).
This leaves you with the parantheses for control structures and the like. If you like layout-based languages, you can adopt the rule that "expression + colon + newline + indented expression 1 + indented expression 2 + ..." is parsed as "expression (indented expression 1) (indented expression 2) ...".
Some examples of code from On Lisp formatted like this:
You can have user-definable infix operators; Haskell has them and uses them to good effect. (The way Haskell does it, you can't have identifiers composed of both letters and operator characters, which Lisp people like to do, but I think we can safely treat that as a matter of taste.) You pick a symbol, say ~, and assign it a precedence and left- or right-associativity:
infixr 3 ~
infixl 7 .!.
Now (x ~ y .!. z) is parsed as ((~) x ((.!.) y z)), where (~) is the Haskell way of making the ~ operator as a prefix function. Haskell also lets you use a prefix function as an infix operator, by putting backquotes around it.
If you want to apply this in Lisp, there is the issue that (foo) means something else than foo; I would like to allow (foo x + bar y) to mean ((+) (foo x) (bar y)), but I wouldn't want (x + y) to mean ((+) (x) (y)). My solution would be that a single value is parsed as just a value, but multiple values next to each other is a function call: (foo x + y) is ((+) (foo x) y), to call y without parameters you have to write (foo x + (y)).
This leaves you with the parantheses for control structures and the like. If you like layout-based languages, you can adopt the rule that "expression + colon + newline + indented expression 1 + indented expression 2 + ..." is parsed as "expression (indented expression 1) (indented expression 2) ...".
Some examples of code from On Lisp formatted like this:
http://himalia.it.jyu.fi/~benja/2007/layoutedlisp.txt
Of course, it still looks like Lisp, with less parens.