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With-Expression.md

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With Expression
Control-Related-Expressions.md

Syntax

'with' param_list 'in' map_expr block_expr

Note that in contrast to most imperative languages like C/C++ or Java, a with-construct is not a statement but an expression and, thus, yields a value.

Typing

A with-expression is syntactic sugar for:

f(args, |param_list, break| -> ! block_expr)

Suppose f has type:

fn(A, fn(I) -> B) -> R

args must be of type A and param_list of type I. Additionally, Impala implicitly declares the following continuation which is usable inside block_expr:

  • break of type fn(B) -> !

    This is the return-continuation of the call to f. Thus, invoking this continuation returns from the current Function Expression with a value of type B.

Since block_expr also exits the current Function Expression, its type must be B, too. The type of the whole with expression is R - whatever is yielded by invoking f.

Semantics

Since a with expression is just syntactic sugar, see Map Expression.

Examples

TODO