partial evaluation definition of partial evaluation in the Free Online Encyclopedia.

(compiler, algorithm)

partial evaluation - (Or "specialisation") An optimisation technique where the compiler evaluates some subexpressions at compile-time. For example,

pow x 0 = 1 pow x n = if even n then pxn2 * pxn2 else x * pow x (n-1) where pxn2 = pow x (n/2) f x = pow x 5

Since n is known we can specialise pow in its second argument and unfold the recursive calls:

pow5 x = x * x4 where x4 = x2 * x2 x2 = x * x f x = pow5 x

pow5 is known as the residual. We could now also unfold pow5 giving:

f x = x * x4 where x4 = x2 * x2 x2 = x * x

It is important that the partial evaluation algorithm should terminate. This is not guaranteed in the presence of recursive function definitions. For example, if partial evaluation were applied to the right hand side of the second clause for pow above, it would never terminate because the value of n is not known.

Partial evaluation might change the termination properties of the program if, for example, the expression (x * 0) was reduced to 0 it would terminate even if x (and thus x * 0) did not.

It may be necessary to reorder an expression to partially evaluate it, e.g.

f x y = (x + y) + 1 g z = f 3 z

If we rewrite f:

f x y = (x + 1) + y

then the expression x+1 becomes a constant for the function g and we can say

g z = f 3 z = (3 + 1) + z = 4 + z

Partial evaluation of built-in functions applied to constant arguments is known as constant folding.

See also full laziness.

Mentioned in	?		References in periodicals archive	?		Encyclopedia browser	?		Full browser	?
No references found	For each agent, the subgroup on cancer in humans proposes a partial evaluation of the human evidence, and the subgroup on cancer in experimental animals proposes a partial evaluation of the animal evidence (Figure 2). The science and practice of carcinogen identification and evaluation by Kleihues, Paul / Environmental Health Perspectives This is due to the inclusion of a partial evaluation of mineralization below 210 meters. Gold Reserve Increases Resource at Brisas by 631,000 Ounces of Gold by Business Wire	Parthian Arsacids Parthian Empire parti Parti Québécois parti-colored buoy parti-coloured partial partial bulkhead partial carry partial Cauchy surface partial cleavage partial coherence partial common battery partial condensation partial correlation partial correlation analysis partial correlation coefficient partial cover plate partial derivative partial differential equation Partial Differential Equation LANguage Partial Discharge partial dislocation partial eclipse partial equivalence relation partial evaluation partial fractions partial function partial key partial molal quantity partial molar volume partial node partial nucleate boiling partial obscuration partial occupancy partial order partial ordering partial partition partial payment partial pediment partial penetration partial plane partial pluton partial potential temperature Partial Pressure partial pressure suit partial prestressing partial product partial recursive function partial regression coefficient partial release	partial differentiation partial differentiation Partial digest Partial Digits Received partial disability partial disability Partial discharge Partial discharge Partial Discharge Inception Voltage partial dislocation partial dislocation Partial disomy Partial disomy Partial disomy Partial Donor Scale partial draw tube partial eclipse partial eclipse partial eclipse partial eclipse Partial eclipses Partial eclipses Partial eclipses Partial eclipses Partial Electron Yield Partial Element Equivalent Circuit Partial Environment Monitor Partial Equalization of Orbital Electronegativity Partial Equilibrium Multimarket Model Partial equivalence relation partial evaluation Partial Evaluation and Program Manipulation Partial Evaluation and Program Transformation Partial Evaluation and Semantics-based Program Manipulation partial excuse partial execution Partial Executions Partial Expiratory Flow-Volume Partial External Biliary Diversion Partial Factor Productivity Partial Fail Partial Failure of Passive Transfer Partial Fetal Alcohol Syndrome Partial File Sharing Protocol Partial First Order Logic Partial Fog Partial Foldover of Subplot partial fraction partial fraction Partial fraction expansion Partial fraction expansion Partial fractions Partial fractions Partial Fractions Decomposition Partial Frame Image Partial Frontolateral Laryngectomy With Epiglottic Reconstruction Partial function Partial functions

Mentioned in

References in periodicals archive

Encyclopedia browser

Full browser

No references found

For each agent, the subgroup on cancer in humans proposes a partial evaluation of the human evidence, and the subgroup on cancer in experimental animals proposes a partial evaluation of the animal evidence (Figure 2).