+The following site may be useful; it lets you run a Scheme interpreter inside your web browser: [Try Scheme in your web browser](http://tryscheme.sourceforge.net/). See also our links about [[learning Scheme]] and [[learning OCaml]].
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+
+1. Function application and parentheses
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+ In Scheme and the lambda calculus, the functions you're applying always go to the left. So you write `(foo 2)` and also `(+ 2 3)`.
+
+ Mostly that's how OCaml is written too:
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+ foo 2
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+ But a few familiar binary operators can be written infix, so:
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+ 2 + 3
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+ You can also write them operator-leftmost, if you put them inside parentheses to help the parser understand you:
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+ ( + ) 2 3
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+ I'll mostly do this, for uniformity with Scheme and the lambda calculus.
+
+ In OCaml and the lambda calculus, this:
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+ foo 2 3
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+ means the same as:
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+ ((foo 2) 3)
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+ These functions are "curried". `foo 2` returns a `2`-fooer, which waits for an argument like `3` and then foos `2` to it. `( + ) 2` returns a `2`-adder, which waits for an argument like `3` and then adds `2` to it. For further reading:
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+* [[!wikipedia Currying]]
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+ In Scheme, on the other hand, there's a difference between `((foo 2) 3)` and `(foo 2 3)`. Scheme distinguishes between unary functions that return unary functions and binary functions. For our seminar purposes, it will be easiest if you confine yourself to unary functions in Scheme as much as possible.
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+ Scheme is very sensitive to parentheses and whenever you want a function applied to any number of arguments, you need to wrap the function and its arguments in a parentheses. So you have to write `(foo 2)`; if you only say `foo 2`, Scheme won't understand you.
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+ Scheme uses a lot of parentheses, and they are always significant, never optional. Often the parentheses mean "apply this function to these arguments," as just described. But in a moment we'll see other constructions in Scheme where the parentheses have different roles. They do lots of different work in Scheme.
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+
+2. Binding suitable values to the variables `three` and `two`, and adding them.