Ponder

[pon-der] /ˈpɒn dər/

verb (used without object)
1.
to consider something deeply and thoroughly; meditate (often followed by over or upon).
verb (used with object)
2.
to weigh carefully in the mind; consider thoughtfully:
He pondered his next words thoroughly.
/ˈpɒndə/
verb
1.
when intr, sometimes foll by on or over. to give thorough or deep consideration (to); meditate (upon)
v.

early 14c., “to estimate the worth of, to appraise,” from Old French ponderer “to weigh, poise” (14c., Modern French pondérer) and directly from Latin ponderare “ponder, consider, reflect,” literally “to weigh,” from pondus (genitive ponderis) “weigh” (see pound (n.1)). Meaning “to weigh a matter mentally” is attested from late 14c. Related: Pondered; pondering; ponderation.

A non-strict polymorphic, functional language by Jon Fairbairn .
Ponder’s type system is unusual. It is more powerful than the Hindley-Milner type system used by ML and Miranda and extended by Haskell. Ponder adds extra recursive ‘mu’ types to those of Girard’s System F, allowing more general recursion. Surprisingly, the type system and type inference algorithm are still not completely understood.
[“Ponder and its Type System”, J. Fairbairn, TR 31, Cambridge U Computer Lab, Nov 1982].
[J. Fairbairn, “Design and Implementation of a Simple Typed Language based on the Lambda-Calculus”, Technical Report No. 75, Computer Laboratory, University of Cambridge, May 1985].
[J. Fairbairn, “A New Type-Checker for a Functional Language”, Technical Report No. 53, Computer Laboratory, University of Cambridge, 1984].
[J. Fairbairn, “Some Types with Inclusion Properties in \forall, \rightarrow, \mu”, Technical Report No. 171, Computer Laboratory, University of Cambridge, Jun 1989].
[Valeria C. V. de Paiva, “Subtyping in Ponder (Preliminary Report)”, Technical Report No. 203, Computer Laboratory, University of Cambridge, Aug 1990].