Let statement throws error on assigning a form to a variable

Question

(let (lineStr (thing-at-point 'line t))
   (body-form......))

throws the error,

call-interactively: `let' bindings can have only one value-form: thing-at-point, (quote line), t [2 times]

Can't a let variable take a elisp form, and eval the form, get its value assigned?

Answer 1

Read the documentation: C-hf let RET

let is a special form in `C source code'.

(let VARLIST BODY...)

Bind variables according to VARLIST then eval BODY.
The value of the last form in BODY is returned.
Each element of VARLIST is a symbol (which is bound to nil)
or a list (SYMBOL VALUEFORM) (which binds SYMBOL to the value of VALUEFORM).
All the VALUEFORMs are evalled before any symbols are bound.

So VARLIST is a list:

(let (...)
  BODY)

And elements which bind values are also lists:

(let ((SYMBOL VALUEFORM)
      (SYMBOL VALUEFORM))
  BODY)

Answer 2

You're missing a necessary set of parentheses around the VARLIST. Your code should look like this:

(let ((lineStr (thing-at-point 'line t))) (body-form......))

(See the documentation for 'let' at 'C-h f let'.) The purpose of the VARLIST being a list is to allow multiple variables to be bound within a single 'let'. The extra parentheses separate the VARLIST from the BODY.