Recursion with lazy functions

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There's a problem with laziness in recursion (with laziness in recursion (with laziness in recursion (with laziness ...))).

Non-recursive lazy functions work as expected, but as soon as a lazyfun is declared in a let rec statement, evaluation is stuck in an endless loop and stack overflows. After investigating a bit (trying factorial and fibonacci functions) I've found out that the problem occurs when arguments are passed to the recursive application. It seems that LazyExpressions passed as recursive application arguments never get evaluated.

https://github.com/0x0f0f0f/minicaml/blob/cfc0537dd8982b6696ba029181ebae956fdeb179/lib/eval.ml#L113-L134

Here's the example I've tried

let rec fib = lazyfun n -> if n < 2 then n else (fib (n - 1)) + (fib (n - 2)) in fib 5

Here's the factorial example

 let rec fact = lazyfun n -> if n < 2 then n else n * fact(n - 1) in fact 5

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Note that the fibonacci and factorial functions work correctly if they are not defined as lazy

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Temporarily removed lazyfun and lazylambda statements.

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The new single argument lambda abstraction fixes this issue.