VDM-10 Language Manual

Chapter 6
Expressions
In this subsection we will describe the different kinds of expressions one by one. Each of them
will be described by means of:
• A syntax description in BNF.
• An informal semantics description.
• An example illustrating its usage.
6.1 Let Expressions
Syntax:
expression = let expression
| let be expression
| . . . ;
let expression = ‘let’, local definition { ‘,’, local definition },
‘in’, expression ;
let be expression = ‘let’, multiple bind, [ ‘be’, ‘st’, expression ], ‘in’,
expression ;
local definition = value definition
| function definition ;
value definition = pattern, [ ‘:’, type ], ‘=’, expression ;
where the “function definition” component is described in section 5.
Semantics: A simple let expression has the form:
✞
let p1 = e1, ..., pn = en in e
✡✝
✆
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