Software metrics have been investigated for the assessment of programs writ-ten in a functional programming language. The external attribute of programs considered in this thesis is their comprehensibility to novice programmers. This attribute has been operationalized in a number of experiments. The in-ternal attribute of software which is examined is the structure. Two models for the structure of software have been employed: callgraphs and flowgraphs. The proposed control-flow model captures the operational semantics of function definitions. The objective measurement of the attributes has been supported by tools. The validation of structure metrics has been addressed in certain ex-periments for programming-in-the-small. The structure of type expressions in functional programs has been analysed in a case study. A simple framework for software metrication proved to be useful. The validation of metrics has been linked with axioms from the representational measurement theory. The control-flow model for functional programs showed its value in the set-up of an experiment regarding the influence of the structure on the comprehensibility. A programming style rule on the use of guards in function definitions has been validated by the findings in this experiment
