This study undertakes a comparative analysis of the learning of functions in Japanese and Indonesian curricula. Using praxeology, a primary construct of the anthropological theory of the didactic, this study analyzed how functions are approached in both countries' school mathematics textbooks. The analysis results revealed a noteworthy contrast: while the Japanese textbooks predominantly define functions as relationships between changing quantities, Indonesians are heavily influenced by mapping elements between two sets. These findings were further explained by how the two countries' knowledge of functions is adapted. In Japan, the notion of functions evolved from proportions, commencing with the modelling of proportional relationships. In contrast, Indonesian textbooks derive functions from relations, with both concepts are introduced after set theory. This study extended its discussion upon the implication of these findings, suggesting an alternative praxeological model for inquiry-based learning about functions.